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Last week, in BAN #1035, I mistakenly wrote that the Psyche spacecraft was swinging past Mars to steal some of its orbital energy and speed up to meet up with its asteroid target. That’s usually why these missions get a gravity assist from planets, but not in this case! The spacecraft was using Mars to change the inclination of its orbit — the tilt it has with respect to the plane of the solar system — to match up with the asteroid Pysche’s^* inclination of about 3°. Changing the tilt of a spacecraft’s orbit is very energy intensive and takes a lot of fuel… unless, that is, you steal that energy from a planet that will never miss it. Anyway, sorry for any confusion.

^* Yes, the mission has the same name as its target. Yes, it really bugs me.

If you’ve spent any time on the internet, then you’ve run across those “Prove you’re not a robot” popups. They’re called CAPTCHAs, and they ask you to click all the images in a grid that belong to some category. They’re all irritating, though the ones that constantly refresh as you click the pictures are the worst. Is that a tiny corner of the crosswalk in that frame? Does that photo of a city intersection have a fire hydrant two pixels high in it? Arg. 

The idea behind them is that the ‘net is infested with bots, automated software that goes through pages and harvests info about them. The bots do this to aggregate stories, or steal them for plagiaristic purposes, or whatever. They’re a curse on the web, and I understand the desire for some sites to try to curtail them.

But I came across one recently that was more confounding than usual, all because I understand science. 

It was one of those “Pick everything in this category” ones, and it really did throw me:

I’d rather walk the planck. Credit: A random damnable web page somewhere.

I’ll admit I was initially baffled by this one, and it got worse the more I looked at it. “Pick everything that produces heat”. OK, well the sun does, obviously. But the steaks don’t; they are hot but don’t produce heat. And if you count the steaks, then you have to include the chair, the ice skates, and the mountain, too!

They’re not “hot” by colloquial standards, but they do emit heat in a scientific sense. I wrote about how this works in BAN Issue 859 in 2025. Basically, a fundamental principle in physics is that anything above a temperature of absolute zero (-273°C or -460°F) emits light. That light has a spread of wavelengths (think of them as colors if you like) that we call a blackbody curve, shaped something like a bell curve with a steep dropoff at shorter wavelengths and a long, declining tail at longer ones. This is also called Planck’s law, if you want to be more mathy about it.

The peak is at a certain wavelength (sometimes called the Wien wavelength) that depends on the temperature of the object. The lower the temperature, the longer the wavelength of that peak. The sun is quite hot at roughly 5,500°C, and emits its peak light in the visible wavelengths. But you emit light too! You have a temperature of about 37°C, more or less, and emit light in the thermal infrared, peaking at a wavelength of about 9 microns. You can’t see that light because it’s outside the wavelength range our eyes are sensitive to, but it’s still light. You’ve probably seen thermal infrared photos or video of people (sometimes called “heat vision”); that works because you emit light at that wavelength.

Even objects we think of as cold do this. Dry ice — frozen carbon dioxide, used to keep frozen products cool for transport — is at a temperature of about -80° C and peaks around 15 microns. Some astronomical objects are so cold they emit very long radio waves! You get the picture.

But CAPTCHA literally doesn’t. That chair, the skates, the mountain, the meat — they all emit light, which in a sense means they all emit heat. 

OK, fine, I may be being a little pedantic here, but I can at least claim I do it because I love to point out fun science coolness (so to speak). But in real life nothing there but the sun actually generates heat; they just are all at some temperature and passively emit energy because of it. And for the record, the “correct” answer for that CAPTCHA included the steak but not the other objects, so it was wrong either way.

In case you still think I’m being pedantic, I recently got this CAPTCHA that is truly a paragon of wrongness:

SERIOUSLY? I MEAN SERIOUSLY, SERIOUSLY? Credit: A website that is openly defying science. 

ARRRRRRRRGGGGGG! “Tap objects that can reflect light”. It took me a sec to realize they meant the water in the creek, but then HOW DO THEY THINK WE CAN SEE THE BED, THE UNDERWEAR, AND THE SOCK? HUH? HUH?

All those objects reflect light. If they didn’t they’d be utterly black. That’s how we see things. Some objects, like the sun and light bulbs, emit visible light (and, as I pointed out above, they all emit light, just at wavelengths we cannot see), and others reflect light. Even the sun can reflect light. It’s not a great reflector, for sure; it tends to absorb most light that hits it, and it emits a whole lot more, plus there aren’t any sources of light bright enough for us to detect a reflection anyway.

So this particular CAPTCHA made me bang my head on my desk. Pedant or not, that one is just plain wrong.

…unless I am, in fact a robot. I can neither prove nor disprove this, but I do know that I know some science. So I will shine a light on it whenever I can, and I leave it to you to reflect on it.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

NASA’S Psyche mission is on its way to the asteroid Psyche (yes, I know, I wish they had named it something else to avoid this confusion), a large asteroid that is apparently made of mostly metal. It’s the largest such asteroid in the main belt, and an object of considerable interest. It was likely once the core of a larger asteroid that got busted apart by impacts, so investigating it is like sending a probe deep into the interior of a planet.

The mission has made one big loop of its trajectory so far, going out into the asteroid belt and then falling back in toward the sun. On May 15^th 2026 it will swing by Mars for a gravity assist (colloquially called a gravitational slingshot): it will steal some of Mars’s orbital energy to accelerate, speeding up its journey out into the main asteroid and giving it the boost it needs to meet up with Psyche (asteroid).[CORRECTION: Oops. It is using Mars to change the inclination, or tilt, of its trajectory to match that of the asteroid Psyche. I wrote a bit more about this in BAN #1307.] Maneuvers like this save fuel, so they can be a vital part of a mission.

Psyche will pass just 4,500 km from the planet’s surface, which is less than the diameter of Mars! So it’s a decently close pass, and it’ll zip past at nearly 20,000 kilometers per hour. It’s been taking observations as it approaches, and thousands are planned both to test its detectors and get more info on Mars, which is always nice. I particularly like this one:

Mars from Psyche when it was 3 million km away. Credit: NASA/JPL-Caltech/ASU

Psyche took this on May 7, 2026 from a distance of roughly 3 million km, and, since the spacecraft is heading back toward the sun from the asteroid belt, it sees Mars as a thin crescent, a view we can never get from Earth. The little extra pieces of the crescent “horns” (technical term: ansae) are sunlight scattered by the planet’s atmosphere (possibly aided by dust and high-altitude clouds). 

Mars is only about 7 arcminutes wide here — the full moon from Earth is more than four times wider, and the camera used has a resolution of about 0.2 arcminutes, so Mars looks pixelated (I also enlarged it a bit so you can see it better). It will get bigger and smoother as Psyche approaches. 

You can watch the raw images roll in at the NASA Psyche website; hopefully I’ll have some fun ones to show you next week. Stay tuned!

I saw some news recently that made me both happy and angry simultaneously, and nothing does that better than news about power generation. An article on EENews reports that California has just started producing energy from a huge wind-power program. It consists of a staggering 916 turbines, which together can generate 3.5 gigawatts of power! An average US home uses about 1 kilowatt of power, so this farm alone could run over 3 million homes. It’s a huge step forward!

That makes me very happy.

However, the company that’s behind it, SunZia Wind, has not been crowing about it. Why not? According to the article, it’s so they don’t catch the attention and ire of the current regime, which could wind up somehow punishing them for this.

That’s not an irrational fear. Because — speaking of irrational — Trump has a bizarre and wholly untethered opinion about wind power, thinking among other things it can cause cancer (it does not). Trump’s also known for being viciously vindictive, making life very difficult for any perceived slights against him. The company’s attitude is prudent.

And that is why I’m also angry. We’ve been immersed in this miasma of right-wing baloney for so long it’s easy to take it for granted, but here we have a prime example of the direct harm it’s causing.

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As of this writing, astronomers have discovered nearly 6,300 exoplanets: alien worlds orbiting alien stars. The first was discovered in the early 1990s. When a new, dedicated mission launches into space the total number found tends to jump up, like when Kepler went into operation, as well as TESS (the Transiting Exoplanet Survey Satellite).

Sometimes there’s a much smaller jump in discoveries when someone digs through the data and finds more exoplanets. At those times we see a dozen more, sometimes a couple of dozen. 

And then there’s the T16 Project. They just published the results of their new technique to look for planets, and where they found 10,061 new planet candidates. 

WHAT.

Yup. They found 11,554 candidate exoplanets in total, but about 1,000 were previously found and another 411 don’t have enough data to be conclusive, leaving the 10,091 new ones. [link to journal paper].

Again, up until now 6,300 have been found. If confirmed, this passel will way more than double the known exoplanets.

The “if confirmed” part is important. Astronomers are a bit conservative when it comes to claims like this, and want to be sure they pass a bunch of tests to make sure everything was done correctly and these planets actually exist. Having said that, the process the astronomers went through looks legit to me, and I would bet the majority of these new candidates are real.

That’s amazing.

TESS works by scanning the sky over and over again, carefully measuring the brightness of every star it sees many times during each scan. If a star has a planet, and we happen to see that orbit edge on, then once per orbit the planet passes directly in front of the star, creating a mini-eclipse called a transit, and the star dims. By plotting the brightness over time — what we call the star’s light curve — we can see a distinctive pattern to the dip in light which can be used to determine a lot about the planet, including its distance from the star and the planet’s size. 

The best way to do this is to see many transits, because if we see the planet orbit around the star several times it gives us a better handle on the planet’s period (its year), and also confirms that the planet exists at all. 411 of the candidates (not included in the 10,091) are single transit events, putting them on shakier ground, but it’s still entirely possible they’re real.

This project looked at data from the first year of TESS observations. They got light curves for a staggering 54 million stars, all brighter than about 16^th magnitude (about one-ten thousandth as bright as the faintest star you can see by eye).

What they did then was detrend those light curves. Some stars are naturally variable, getting brighter and dimmer over time. Sometimes there are instrumental effects that affect the light curves, and so on. The astronomers applied various mathematical fits to the curves, then used that to “flatten” the curves and get rid of those trends. This makes any small transit dip far easier to spot.

Raw data of a star (top) showing a sinusoidal oscillation and a gradual rise in brightness, both of which are due to detector issues. (Bottom) The same plot but detrended, making it easier to see the very small transit dips. Credit: Roth et al. 2026 

They used a form of neural net to analyze the data, basically an algorithm that can be “trained” to look for features in the light curves, and be able to tell real effects from false positives. That’s how they winnowed down the number to just over 10,000 planets.

By the nature of the observations, they tend to find big planets close-in to their host stars, because these make bigger dips and do so with shorter periods (so the transits are seen more often). The majority of the planets they found have periods of 3-4 days. Yes, days. We call these planets hot Jupiters for a reason; they are extremely close to their host stars (which is why their periods are so short) and get cooked by them. These orbits are typically perhaps 10 million kilometers in radius; for comparison Mercury — the closest planet to the sun, with a surface temperature hot enough to melt lead — is about 50 million. So yeah, these planets are broiling.

A histogram that shows the number of exoplanets found versus their periods. Most planets have a period of about 3-4 days. Credit: Roth et al. 2026

There may be longer-period planets in the data too (like those 411 single-transit ones they found) but these are harder to confirm, and by the nature of the geometry are more rare the farther out the planet is. In fact, while the transit method of finding exoplanets works very well, it misses the vast majority of planets because their orbits aren’t edge-on. We can look at the geometry of orbits, though, and extrapolate up to how many should exist from what we do see, and that’s how we find that, on average, every star in the galaxy has one planet. In reality, though, some don’t have any, while some, like the sun, have many.

But either way, there are hundreds of billions, perhaps trillions, of planets in our Milky Way galaxy alone.

Mind you, this new result is based on only about 15% of the TESS data, too (it’s been observing for over eight years now). The first year didn’t cover the whole sky, and as more observations are processed fainter stars will be seen, too. So as they continue this work to cover the entire current observations set they expect to find even more planets.

This is the power of a General Observer mission, where the data are archived and made public, so that scientists from around the world can get them and figure out new ways to analyze them. Before T16 published their results there were 885 confirmed planets found using TESS, and just shy of 8,000 candidates. That latter number just went way up.

The implications of this are phenomenal. We already had decent statistics on the number of stars with planets, and are getting good stats for the kinds of planets seen, too — hot Jupiters, super-Earths, mini-Neptunes, and more. But the more we find the better those statistics get, and the more we understand about how stars make planets. And while there are many scientific goals for these studies, one that resonates with us as humans is the search for other Earths: planets the right size and distance from their host stars to possibly have conditions similar to our own home world. Those are hard to find; Earths are small and the longer period makes them difficult to spot.

But, given the statistics, they’re out there. And we’ll find them.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

A star is generally defined as an object large enough to have sustained nuclear fusion going on it is core. “Planet” doesn’t have a great definition, but they form around stars from a protoplanetary disk that contains material leftover from the star’s formation.

In between the two lie the brown dwarfs: intermediate objects that are massive enough to fuse lighter elements like deuterium (an isotope of hydrogen) and lithium, but quickly run out of fuel and become, for lack of a better word, inert. 

The range of brown dwarf masses is very roughly 13 to 77 times the mass of Jupiter — it depends on a lot of characteristics besides mass, but this is a decent rule of thumb.

But there’s more to it. Stars form from the direct collapse of gas from a gas cloud as it shrinks and forms a disk; this is called fragmentation. Think of it as top-down formation. Planets form as smaller bits of rockier materials in the disk clump up, growing bigger and bigger, colliding and merging, until a planet arises. This is called core accretion, and you can think of it as bottom-up formation.

Brown dwarfs, irritatingly, sit between these two mass regimes. Which way do they form? More massive ones, closer to stellar mass, probably form like stars, from fragmentation. But with ones closer to the lower limit the formation mechanism isn’t clear.

 29 Cygni b is the small fuzzy dot to the lower left, and the star-shaped icon marks the position of the blocked-out host star. Credit: NASA, ESA, CSA, W. Balmer (JHU, STScI), L. Pueyo (STScI). Image processing: A. Pagan (STScI)

To look into it, astronomers observed 29 Cygni b, an object with a mass of about 15 ± 5 times that of Jupiter, putting it right on the “deuterium limit”, the lowest mass object that can fuse deuterium. So it may be a very low-mass brown dwarf or a very high-mass planet. The host star is an A-type (about twice the mass of the sun) roughly 133 light-years from us [link to journal paper]. 

On top of that, 29 Cygni b orbits the star pretty far out, about 2.4 billion kilometers away, a bit closer in than Uranus orbits the sun. That far from the star the protoplanetary disk isn’t very dense, so it’s hard for planets to form from accretion. In that case they likely either form farther in and get gravitationally tossed out by a close encounter with another planet, or they form from fragmentation.

When it all clicks.

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One thing that separates the two processes is the amount of heavier elements the planet draws in. Fragmentation tends to generate lower amounts of these elements (like silicon, carbon, and oxygen), whereas accretion by definition gets more of them (since you need rockier materials to glom together; also, this tends to draw in more material with heavy elements in it later on due to some complicated physics).

The astronomers used JWST to take a peek at 29 Cygni b. It’s far enough out from the star that they could get direct images of it by using an occulting mask (basically a disk or bar of metal in the pathway light takes inside the telescope) to block the star’s glare, allowing the fainter companion to be seen. They used filters that pick out the infrared light emitted by carbon dioxide and carbon monoxide molecules, because that can be used to find the ratio those two molecules in the companion’s atmosphere, and from there how abundant heavier elements are.

What they found is that the ratio does lean toward the companion forming bottom-up, through accretion, so more like a planet than a star.

Artwork of an exoplanet/brown dwarf with its star in the background. In silhouette, a small icy moon can be seen erupting with geysers. Credit: NASA, ESA, CSA, J. Olmsted (STScI)

They also did a clever follow-up, using an interferometer to look at the star itself. This is a technique that allows extremely high-resolution images on very tiny areas of the sky, so hi-res that the shape of a star can be detected! A-type stars are fast rotators, and tend to be oblate, flatted, due to centrifugal force. They measured that for the star, and found the planet orbits in more or less the same plane as the star’s equator. Protoplanetary disks tend to form in the equatorial plane, so again that implies the companion formed like a planet, not a star. This isn’t a smoking gun, but it does lend credence to the accretion mechanism.

 That’s pretty interesting! If this holds up it shows that objects can form like planets even past the deuterium limit, well into the brown dwarf regime (assuming the mass of 29 Cygni b really is 15 Jupiters; the uncertainty of 5 Jupiter masses up or down is a bit large for my taste to be sure).

I am pleased to announce that I won an award for an article I wrote!

Every year, the Solar Physics Division of the American Astronomical Society (the largest group of professional astronomers in the US) gives out a slate of awards for science communications, called the Popular Media Awards. This year, I won for my article, “Could the Sun Fry Earth with a Superflare?” published on May 2, 2025. 

The category was for scicomm done by a scientist, which, fair enough. I’ve never really been able to categorize myself — I’m not really a journalist, and I haven’t done scientific research in a while. So I just think of myself as a scicommer.

I got a smile, too, that I won for an article about our planet getting cooked by a cosmic disaster; that’s kinda my thing.

My thanks to everyone on the award committee! It’s an honor, and I truly appreciate it.

Earth is warming up, changing our climate drastically, and not in a good way. Hurricanes get more powerful, tornados do more damage, we get rain and drought and sea level rise and ocean acidification and you get the idea.

What can we do about it? One idea is to somehow make Earth’s atmosphere more reflective, so we don’t get as much incoming sunlight. Less light = less heat = less warming. This is part of a category of ideas called geoengineering, where we change something about the planet to mitigate warming.

One of the ideas is called stratospheric aerosol injection, or SAI. Aerosols are particles that can be suspended in air, and the stratosphere is the layer of our atmosphere that starts roughly 10-20 kilometers above the ground (depending on latitude) and goes up to about 50 or so km. “Injection” seems obvious enough: the idea is to dump a lot of teeny particles of some substance into the air that then remain suspended in the stratosphere, reflecting sunlight.

There have been quite a few studies about this, and some people take the idea seriously. But a study has come out showing that the effects of this are difficult to predict, and the outcomes make it risky [link to journal paper].

Sunrise during a 2020 Colorado wildfire, where the smoke dimmed the sun considerably. Credit: Phil Plait

Now, on a zero-to-duh scale I’d rate this conclusion as about a 15. We really don’t understand geoengineering at all, and we do know that a lot of effects are non-linear; that is, you change a small thing and it can affect multiple other things, which then affect even more other things, and you wind up getting an outcome you can’t predict and that can be wildly different given small changes in the input.

But this paper actually outlines a lot of real-world problems with SAI. For example, what do you use to reflect sunlight? Some kinds of tiny grains are expensive, and you need so much (millions of tons!) that it can affect the market, ramping up prices. Others are easier to obtain, but their actual properties make them harder to use; they can clump up, for example, increasing the grain size and reducing their reflective properties.

Another problem is that, as you’d expect, there are unexpected effects. For example, volcanic eruptions put a lot of sulfur aerosols into the atmosphere, and we’ve seen temporarily cooler temperatures from that (like after the Pinatubo eruption). However, this can change rainfall amounts in various locations, and even affect the ozone layer. Polar injections can cause changes in monsoons. Sulfur eventually dropping down can cause acid rain as well.

My worry about this on the theoretical side is that it’s impossible to model all the effects, especially on the biosphere. Non-linear effects, especially in Earth’s atmosphere, are ridiculously sensitive to even small changes, and the equations are fierce. There are always unintended consequences, and they might be mild, or they might be catastrophic.

My worry on the practical side is that some dunderheaded egotistical billionaire might just decide on their own to go ahead and do this, and it winds up being a catastrophe, because any time a billionaire gets it into their heads to do something like this it always is.

To be clear, I am against using our only planet as an experimental lab. 

The flip side of this, though, is that we already do. We’ve been running a decades-long experiment of dumping billions of tons of carbon dioxide into the air annually, and we know how that’s turning out. Don’t let the climate science deniers fool you: global warming is 100% our fault.

So sure, especially given we’re the cause, it seems like doing something to mitigate this is a good idea… but this ignores the incredibly obvious idea that WE SHOULD STOP RUNNING THE EXPERIMENT. We need to decarbonize our energy production and stop the greenhouse gasses from getting into the atmosphere in the first place. This won’t reduce the problem — and least not for a long time, since CO₂ has a long half-life in the atmosphere — but it will stop it from getting worse. Then perhaps we can start doing something to reduce the amount in there.

And also to be clear, I am all for investigating geoengineering in a theoretical sense; let’s talk about and scientifically analyze different ways of reducing CO₂ or reflecting sunlight or whatever, but let’s do it in a sober, judicious way, and not run off half-cocked and potentially make a serious problem even worse.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

Dark matter is the catchall term astronomers use for some sort of matter in the universe that doesn’t emit light, and doesn’t interact with “normal matter” (the kind we’re made of, with protons and electrons and such) except through gravity. We know it exists, and that by mass it outweighs normal matter by about five to one. 

The problem is, because this stuff is dark and doesn’t talk to normal matter, detecting it is extremely difficult except through indirect means. We can see how the gravity of dark matter affects how galaxies rotate and how they move through galaxy clusters, and even how it affects the light of background galaxies through gravitational lensing. But we don’t have a grip on what dark matter actually is. Best guess is that it’s some sort of subatomic particle, possibly axions, but no one is really sure.

The leading idea is that it’s what’s called cold dark matter, or CDM, which means the particles don’t move rapidly (so it’s cold; temperature is literally a measure of how rapidly particles move). Using the physics of how this matter would behave, it’s possible to reproduce a lot of the structure and behavior we see in the universe.

However, maddening inconsistencies remain. CDM predicts there should be many more dwarf galaxies then we actually see. It also predicts far fewer strong gravitational lensing sites than we actually see. There are a few other problems that get pretty detailed and specific, but suffice to say CDM works for the overall picture but doesn’t seem to get the details exactly right. 

So scientists introduced an idea of a different kind of dark matter that interacts with itself via some as-yet unknown force, similar to how, say, protons and electron interact via the electromagnetic force. This is called self-interacting dark matter, or SIDM, and it does seem to help with some problems. 

A simulated map of dark matter in the universe showing it as a series of interconnecting filaments where galaxies form. The scale of the map is over a billion light-years across. Credit: Millennium Simulation / Max Planck Institut für Astophysik

But not all. So a team of scientists has come up with an interesting idea: maybe dark matter isn’t all one thing [link to journal paper]. Instead of it being a single kind of particle, maybe it’s more than one, and they have different masses.

This idea introduces a key factor into dark matter: mass segregation. We see this with normal matter; if you have a cluster of stars, ones with more mass tend to settle to the center while lower mass ones are flung out into the suburbs. This is because when two object interact, they tend to share their energy of motion. When a massive object moves past a lighter object close enough that they can interact via gravity, the massive object gives some of its energy to the lighter one, slowing the massive one and speeding up the lighter one. If they’re in a cluster, this causes the beefier object to drop down to the center.

The same thing could happen with dark matter. In a huge cloud of gas, like one big enough to condense and form a galaxy, the heavier DM particles interact with the lighter ones through some weird dark force, and the heavier ones sink to the center of the cloud while the lighter ones get sent outward. 

Using some simple assumptions about the mass ratio of the DM particles and the force they interact with, the scientists show that this leads to a distribution of dark matter that naturally reproduces much of what we see that CDM doesn’t explain well. It still needs a lot of work, but this is an opening salvo into a new idea that could resolve a lot of the problems remaining in CDM.

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Hey folks, a quick ask for y’all: I have an invitation to speak in the Los Angeles area on November 14, 2026. I enjoy giving public talks! I really would love to be able to give more while I’m in town there. If any of you have contacts at museums, community groups, schools, or whatnot that might enjoy having me come speak about astronomy, please let me know! Or better yet, my speaking agent Beth Quittman (info@samaraspeakers.com) of Samara Speakers Agency, that would be lovely. Thanks!

I’ve written about the Sombrero Galaxy many times before. It’s relatively nearby (30 million light-years away), and bright enough to be a favorite target for astronomers. It’s a nearly edge-on spiral with two prominent features: a striking dark lane of dust across the midplane of the disk, and a vast smooth halo of stars surrounding it. It’s been imaged in detail by Hubble, JWST, and many more observatories. It’s gorgeous.

I’ve also written about DECam before: an insanely huge 570-megapixel (!) camera mounted on a 4-meter telescope, designed in a way to see a staggering 2.2° on a side of the sky — the moon is about 0.5° across, so this is an immense chunk of sky to see at one time for such a camera. It’s designed to look at millions of galaxies to understand better how dark matter and dark energy have sculpted the cosmos.

So, combining these two, here is a very cool and somewhat unusual view of the Sombrero with DECam:

The Sombrero Galaxy via DECam. Credit: CTIO/NOIRLab/DOE/NSF/AURA; Image Processing: T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), D. de Martin & M. Zamani (NSF NOIRLab)

Daaaaang. Most images show the galaxy itself filling the frame, but I love this one because it puts the Sombrero more in context, surrounded by stars and faint galaxies.

In the profoundly huge 14,000 x 9,000 pixel version several things stand out. One is that the halo of stars around the galaxy goes for a long way, stretching far outside the main disk. This is true for most big galaxies, including our own, but the Sombrero’s halo is much brighter than most. This is likely due to a collision with another galaxy, which can strip stars away and put them on far-flung orbits. The dark lane of dust across the middle is likely from that collision as well; most galaxies don’t have such an intense lane like that. It may have collided with a dust-laden galaxy; the gravity of the bigger galaxy then stripped out that dust which went into orbit around the big galaxy’s center.

There’s also a faint loop of material to the lower right as well, and that too is from a collision; it’s made of stars stripped from a smaller galaxy that came too close to the much larger spiral. There’s a hint of it at the upper left as well.

It’s well known that the Sombrero is also surrounded by about 2,000 globular clusters, ancient collections of hundreds of thousands of stars held together by their own mutual gravity. Compare that to our Milky Way, which only has 160 known! I’m starting to think the Sombrero is something of an overachiever. Anyway, I searched the high-resolution image of the Sombrero to look for them, but honestly there are so many stars and so many small fuzzy background galaxies I couldn’t positively identify any. Maybe you’ll have better luck. 

But this new image got me thinking about the Sombrero. I’ve actually never seen it for myself through a telescope. It’s part of the Virgo Cluster of galaxies, and is getting higher in the southeast part of the sky after sunset as summer approaches. I’ll have to try for it; I have dark skies here in nowheresville Virginia, so I bet I can spot it with binoculars. I’ll put it on my todo list! 

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Speaking of big, nearby spiral galaxies…

You’ve probably heard that in some billions of years time, our Milky Way Galaxy and the Andromeda Galaxy are due to collide, merging into a single larger galaxy as chaos ensues in them both.

I’ve written about this event many times, and (to toot my own horn) I’ve been one of the few voices out there throwing some skeptical cold water on the conclusions. Back when the results were first announced the merger seemed inevitable, but papers started coming out showing that that may not be the case; Andromeda’s approach toward us (or the two of us approaching each other if you prefer) has some sideways motion to it as well. If that tangential velocity is high enough, the two galaxies will miss each other.

The slide to the side is very difficult to measure, because you have to physically see the stars in the Andromeda Galaxy move over time. Given they’re 2.5 million light-years from us, that motion is teeny tiny, and you have to observe the galaxy over many years to see any motion at all. Even then, uncertainties in the measurement make it really hard to know exactly how fast the galaxy is moving. The last time I wrote about this, for Scientific American in August 2024, researchers looking at the gravitational influence of other galaxies around us on the collision concluded there was a 50/50 chance of a collision, and if it does occur it’ll be in about 8 billion years.

Artwork of the sky’s distant future: as the Andromeda Galaxy approaches it will loom large in the sky next to our more usual view of the Milky Way, as seen past silhouetted mountains on Earth. Credit: NASA, ESA, Z. Levay and R. van der Marel (STScI), T. Hallas, and A. Mellinger

Welp. New research has just been published that builds on that. Starting with the same assumptions, these scientists used updated measurements from the Gaia spacecraft of stars’ motions in both Andromeda as well as the Triangulum Galaxy, the third largest in our Local Group of galaxies and the one with the strongest outside gravitational influence on the potential collision. With these new data they find the collision probability goes up to 90%, with a median merger time of 6.5 billion years from now.

BUT! They also show that this depends sensitively on their input assumptions, and the probability can range from 64% to 100%, depending on what parameters they use. So, aggravatingly, even after all this we can’t be completely sure a collision will take place! It’s probably the way to bet, but certainty still eludes us. 

The thing is, our understanding will get better over time, because the longer we do observe Andromeda the more the stars will move, and the easier it gets to see that motion (think of it like seeing a distant bird flying; its apparent motion is small so it’s hard to know what direction it’s moving, but if you wait long enough that gets easier to see).

So the jury is still out on any future existence of Milkomeda, but time will tell.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

The final hours of the subscription sale

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Reminder: If you want to upgrade from being a free subscriber to premium, the nearly 50% off sale to $3.20/month (for the first month) or $32/year (for the first year) ends TODAY at 4:00 p.m. Eastern US time (I had originally said noon, but then realized that’s not much time after this issues goes out for folks to jump in).

Sign up here! After the sale ends the prices go back up to $6/month and $60/year, so get the cheaper price while you can! And, as always: THANKS!

Drawing of Voyager. Credit: NASA/JPL-Caltech

Well, this kinda sucks, but it’s no surprise: another scientific instrument onboard the Voyager 1 spacecraft has been turned off.

On April 17, 2026, engineers switched off the spacecraft’s Low-energy Charged Particle Detector, a device that measures the energy, direction, and composition of subatomic particles zipping through space.

It was shut off because the device powering the spacecraft, a radioisotope thermoelectric generator, is losing power all the time, and can no longer keep all the subsystems on the spacecraft operating. As I wrote in BAN #856 on March 2025, other instruments have been turned off over time for the same reason.

Losing the detector means an extra year of power overall for Voyager 1, which is the trade made. It still has other instruments working, which is really important: it’s over 25 billion kilometers from Earth, measuring an environment that is essentially interstellar space. That’s not something we can easily do, and doing so in situ is up to basically just Voyager 1 and its twin Voyager 2.

More events are planned, including shutting down a lot of instruments all at once to use lower power consumption devices instead. Tests for that are planned in May and June, and if that works it will be fully implemented as early as July. Stay tuned.

Waves on Titan (left) are much higher than they are on Earth (right) at the same wind speed. The floating red ball is one meter wide, and the marks on the sticks show one-meter heights. Credit: Schneck et al. 2026

If you’ve ever stood on a beach looking over the ocean (or a big lake; I remember days on Lake Michigan like this), you can see waves rolling in toward land. These waves are wind-generated; as the wind blows over the surface of the ocean the water moves with it, piling up a bit. The energy from the wind is transferred to the liquid, moving through the water horizontally, and the water moves up and down in response. It’s actually a fairly complicated physical effect, even though it seems familiar.

The equations behind it are fierce, and involve many parameters like the liquid density and viscosity (how easily the liquid flows), the wind density and speed, and more. Even (especially!) the gravity. 

These conditions are different on different worlds, so the waves we’d see on them would be different, too. 

A team of scientists were curious about this, so they created a physics-based computer model that crunches the numbers to determine how waves grow on alien worlds [link to journal paper].

First, as a sanity check, they used it to model waves on Earth, and got numbers that corresponded to real-world measurements. So that’s cool. 

Then they tried it for other places. Titan is the largest moon of Saturn, and is the only other large body in the solar system we know of with liquid on its surface. However, that liquid is actually methane, not water! Titan is extremely cold (about -180°C), so methane is a liquid there. Titan has an atmosphere of nitrogen that’s actually denser than our own air, despite the lower gravity (about 1/7^th Earth’s). 

That makes thing different indeed. Not only that but liquid methane is much less dense than water (somewhat less than half, if I’m reading that page correctly) and also much less viscous, so waves there should be quite different than here.

That’s what the scientists found: waves begin to grow at lower wind speed and grow to higher amplitude than they do on Earth. That’s what I’d expect given the conditions, but it’s nifty to see the physics back it up. For example, on Earth a wind speed of 10 meters per second — 22 miles per hour, which is pretty brisk — creates waves two to three meters high with max heights around 5 meters. On Titan that same wind speed creates wave 15 meters high that peak at 40 meters. That’s higher than even rogue waves on Earth!

They found this to be the case at all wind speeds; at a few meters per second on Earth the wind barely gets the water to move at all, but on Titan that same speed generates waves several meters high! 

Titan may be a better place to surf than Santa Cruz. You’ll freeze to death, maybe even before you suffocate, but still.

One thing though: the waves move more slowly. That might be good for beginners. You can see that for yourself in a video the scientists made, showing waves on Earth (right) versus Titan (left) at the same wind speed:

Cooooool.

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As I wrote in Ban 1024 (the 2^10th issue!), I’m having a big sale on premium subscriptions to this here newsletter: the price is US$3.20 per month or US$32 per year! The conditions are listed out in that issue so please check it out. The sale ends at noon Eastern US time Thursday (April 23, 2026). This applies to new subscriptions only, but if you’re already a paid subbie you can still get a gift subscription for another astrodork in your life.

Sign up here! And thanks for your support.

The Vera C. Rubin Observatory has been in testing mode for a while now, and will soon begin routine scientific operations, where it will scan huge chunks of the sky every night looking for transients: objects that change their brightness or positions in the sky. This includes exploding stars, flaring black holes… and a lot of much solar system objects in our cosmic back yard.

I’ve already written on how 2,000 asteroids were discovered in early observations. Well, scientists just announced that looking at early images taken over the course of about six weeks, they have now found a staggering 11,000 asteroids. Eleven thousand.

Those are new discoveries, previously unknown rocks mostly orbiting in the Main Belt between Mars and Jupiter. It also spotted an addition 80,000 previously known asteroids as well! Holy wow. Many of those are what are called recovered asteroids, ones that were not observed long enough initially to get good orbits for them, so they became lost. Rubin has found them again, adding a long time baseline of observations that help nail down the shapes of their orbits.

Asteroids (shown in light blue) discovered by Rubin is it looked in various directions in the sky. Credit: NSF–DOE Vera C. Rubin Observatory/NOIRLab/SLAC/AURA/R. Proctor Acknowledgements: Star map: NASA/Goddard Space Flight Center Scientific Visualization Studio. Gaia DR2: ESA/Gaia/DPAC. Image Processing: M. Zamani (NSF NOIRLab)

Here’s an animation of the discoveries, which come in bursts as observations were made. You can see the orbits of the inner planets and Jupiter, with asteroids in between as a blue fog. As Rubin looks in one part of the sky as seen from Earth, asteroids are discovered along that physical track, which appear as lighter blue dots (and their motions are continued as time goes on). You can get more info by reading the notes for the video on YouTube.

In that 11,000 space rock haul are 33 near-Earth objects, asteroids that get relatively close to Earth as we both orbit the sun. None of them gets close enough to be a threat however. I expect, though, that over time Rubin will find plenty of those (called Potentially Hazardous Objects), too.

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Incidentally, a paper has just been published where scientists ran simulations of how Rubin will see imminent impactors, (typically small) objects that are about to hit Earth [link to journal paper]. About a dozen of these have already been spotted (to be clear, I mean rocks that were found right before they hit our atmosphere, sometimes just hours in advance), almost all from the northern hemisphere. Rubin is in the Chile, so this will help us spot these smaller rocks. The scientists find that the observatory should catch one or two of these in the meter-size range per year, usually from about 1 – 3 days before impact. These rocks are small and therefore faint, which is why they typically aren’t seen until right before they burn up in our atmosphere. So this is good news too.

It also spotted 380 trans-Neptunian objects (TNOs), icy and rocky bodies that orbit the sun out past Neptune (you can think of Pluto as being the largest of these). Only about 5,000 TNOs are known, so in just a month and a half Rubin added about 8% more to that. After the sky survey is completed in about a decade, it should have found tens of thousands of these objects! That’s super important: the more we find, the more we can classify them by size and orbit. Our knowledge of this distant solar neighborhood is spotty, and Rubin will help us get a much better map of it. 

I’ll note that Planet 9, a still unconfirmed object potentially larger than Earth orbiting the sun very far out, was found due to its alleged influence on TNOs. Once we find lots more, that could help nail down its existence. It could even spot P9 directly! Time will tell.

Rubin hasn’t even really opened up for business yet and it’s already doing incredible work. I cannot wait until it’s up and running at full capacity. We’re going to learn so much about the changing sky.

You can keep track of Rubin’s asteroid discoveries on the Rubin Asteroid Discovery Dashboard. There’s also a cool interactive interface for exploring what it’s found (though it’s a CPU and RAM hog). It’s fun to poke around these.

• A Kuiper Belt Object called Altjira was thought to be a binary object, but new work indicates it’s likely actually a hierarchical trinary (with two objects orbiting each other and a third orbiting the two farther out); only one other such object is known, and these can help understand the dynamics of objects out past Neptune [link to journal paper].
  

• Many Kuiper Belt Objects are binary, and some are contact binaries (like Arrokoth, where the two components physically touch, making a snowman-like double-lobed body) — but models of formation have difficulty reproducing them. New work shows that a collapsing cloud of small pebbles can naturally create contact binaries of various lobe shapes and sizes [link to journal paper].

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

<tl;dr> I’m running a big subscription sale right now where a monthly subscription is $3.20 for the first month and an annual subscription is $32 for the first year!

We here at the Bad Astronomy Newsletter HQ (and by “we” I mean me, and by “HQ” I mean my office in the basement of my house where I’m usually sitting around in PJs) recently celebrated the occasion of the publishing of the 1000^th issue of this newsletter. Being a human with ten fingers, mentioning the third power of that number’s issue seemed appropriate.

Yet I am more than a human: I am a geek. Deeply, deeply nerdy. So, more important than that 10³ issue is the one you are currently reading: Issue 1024, or Issue 2¹⁰ . As you probably know, computers use base 2 for calculations, so any power of 2 is important, but this one comes up a lot in life; for example it’s the basis of the kilobyte for computer memory, and the number of pixels on the side of Hubble’s STIS CCD detector! Don’t even get me started with powers of two and fast Fourier transforms.

Like I said: deeply nerdy.

But there’s more: By a pretty fun coincidence, I also published the first issue of BAN on April 16, 2018, which makes today the 8^th anniversary of the newsletter as well!

So this issue is a double kilometerstone, and one worth celebrating.

That’s why I am throwing a big ol’ premium subscription discount sale at y’all. In the past I’ve usually done a 20% discount, but that doesn’t work with our base-2 theme, so instead I’m keeping it binary.

The normal rates are US$6/month and US$60 year, but for this discount they’ll be 2⁵ -based:

$3.20/month and $32/year (US dollars)!

(2 x 2 x 2 x 2 x 2 = 32, just to be clear.) 

In human terms, that’s very nearly a 50% discount!

This sale will be for one time unit of subscription: if you sign up for a year it’s good for that first year, and if you sign up for a month it’s good for that month; after that period the price will go back to the undiscounted rate.

The discount will be applied to all new subscriptions, and will be valid for a duration of one week (ending April 23, 2026 at noon Eastern US time). All you have to do is go to the signup page, enter your email, and when given the option choose the “Premium subscription”. You’ll see the discounted rates listed. After that it’s the usual process of paying for something online.

SIGN UP HERE!

What do you get as a premium subscriber? For one, you’ll receive three issues of the Bad Astronomy Newsletter every week instead of one (they’re sent out on Mondays, Tuesday, and Thursdays). That’s 156 per year, which, given their length, is roughly two full science books worth of articles every year. You also get access to the full archive of newsletter, 1024 strong as of today. You can also join the BAN community and leave comments on the articles — you can comment, ask questions (I try to answer them quickly), and discuss stuff amongst yourselves. It’s a good group.

[If you’re already a premium subbie: Thanks! But I’ll add you can give gift subscriptions, too. Just go to the signup page and enter their email address. After that you’ll be sent to a page that lets you choose some options. First, click the “Gift” button, then choose the subscription duration.]

Also, I sometimes run ads for various things here, and those are not visible to paid subscribers. If you hate ads, well, there you go.

And finally you’ll know you’re supporting my ability to publish this newsletter at all. I’m a freelancer, and even though I write for Scientific American as well I still need to pay for health insurance for me and my family and all that. I’ll be bluntly honest and say that without my premium subbies I would be in big trouble indeed. They keep me afloat financially, and I appreciate every single one of them.

And that means you get my very sincere thanks.

So please sign up! And in return I’ll do my best to bring the cosmos to your emailbox thrice weekly. To the edge of the observable universe and back, I thank you.

And now for some astronomy…

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Y’all know by now I’m a sucker for a beautiful nebula: a cloud of gas and dust in space. These take many forms, including when stars like the sun die, when massive stars die, and — in this particular case — where stars are being born.

Sharpless 2-305 is one such star-forming region. Its distance isn’t perfectly known but it’s probably about 10 – 13,000 light-years from us. It’s huge, and making a lot of stars: there is about 3,000 times the sun’s mass worth of stars in it (which likely means many stars more than that, since lower-mass stars are more common), so it’s actually making a star cluster, called Mayer 3. The stars in the cluster are young, less than 2 million years old on average. Many of them are massive stars, and in fact the nebula is being lit up by two powerful O-type stars, blasting it with intense light.

But why talk so much when I can just show you:

Sharpless 2-305 in the infrared. Credit: Mark McCaughrean (MPIA) / NASA, ESA, CSA / CC BY-SA 4.0

HOLY WOW.

[Click here to get the much larger 6,100 x 6,800 version, because yes you want it.]

This image was taken using JWST by astronomer Mark J. McCaughrean; he and I have been chatting about some of his JWST observations for a while now (and I have another one for you I’ll write up soon because yegads it’s also incredible). He sent me this image just so I can show it to you here on the BAN. 

It uses three JWST filters: what’s displayed as blue is actually the 1.82 micron filter (which sees redder stars, as well as water and methane gas), green is the 3.0 micron filter (water ice, typically), and red is 3.6 microns (which sees cosmic dust in the form of long sooty chains of carbon molecules). Mind you, this is all in infrared which we cannot see with our eyes, but the individual images have been displayed using these colors so we can see and interpret them. The reddest light the eye can see is about 0.75 microns, for comparison.

The star cluster is obvious, sitting to the upper right of center (note: the six “crosshairs” you can see in bright stars are called diffraction spikes; they’re due to optical effects inside the telescope and aren’t real). The light from the most powerful stars in the cluster has carved a huge cavity in the gas, creating a thick shell of material around them — the blue fog permeating the inside of the nebula is gas zapped by light from the big stars. The inside edge of the bubble has thick “fingers” of material pointing to the center; these are where the gas and dust is thicker and harder to erode, like sandbars in a stream. What’s left are those fingers pointing toward the most luminous stars (you can see there are two of them very close together just to the right of center).

Detail on the finger to the lower right of center. Credit: Mark McCaughrean (MPIA) / NASA, ESA, CSA / CC BY-SA 4.0

I’ll note the nebula looks very different in visible light, the kind we see. This Very Large Telescope (VLT) image, for example, really highlights hydrogen gas in visible light (the kind we see with our eyes), and it almost looks like a different nebula. The little glowing upside-down red-rimmed V structure to the lower right in the VLT image is the same as the tower in the lower right of the JWST image, if that helps. The cavity isn’t nearly as obvious, either, but if you look carefully you can see the same stars in both images in places. That’s not easy, either, because some stars are bright in infrared but dim in visible light, and vice-versa. IDing them can be a chore.

The texture and detail in the JWST image are just spectacular. Infrared light can generally pass through denser dust than visible light can, so dark regions in the nebula are really dense knots of material. These tend to be where new stars are being born; the material is dense enough to collapse under its own gravity to form stars.

In fact, take a look at the lower left corner. That intensely bright star isn’t actually a star, at least not yet: it’s a protostar, caught in the act of forming. Called RAFGL 5232 (among many other names derived from different catalogs), it’s already massive, with about 11 times the mass of the sun! It’s blasting out light at a rate 13,000 times that of the sun, too, which is why it’s booming out in the JWST image. Weirdly, though, it’s far fainter in visible light, since the dense junk around it absorbs most of that light (it’s just barely in the VLT image at the lower left, but is so much fainter it’s not obvious at all).

Here’s a close-up of that fetal star:

The protostar RAFGL 5232. Credit: Mark McCaughrean (MPIA) / NASA, ESA, CSA / CC BY-SA 4.0

Look at all that material being affected by the almost-star’s light! I love the multi-colored ribbon below it. Spectacular.

This shows the power of using JWTS combined with other telescopes like Hubble or VLT or Chandra: you see different structures in different wavelengths of light, and wholly different objects are revealed. We also get an idea of what’s inside these structures, what elements and molecules are strewn about. That’s always important, and in this case tells us a lot about the environment in which all these stars are forming. 

In fact that’s why these images were taken, to examine the range of stellar masses of the newborn stars to see how many low-mass ones are forming compared to higher masses, what’s called the stellar mass function (I wrote about this sort of thing here on the BAN as well as in Scientific American). That’s a critical component to understanding how stars are born.

And that’s important. Our planet happily orbits just such a star, and we’re learning more about it all the time (like, it was almost certainly born in a huge cluster not too different from Sharpless 2-305).

I for one like to understand the neighborhood I live in. It’s just that astronomers have a much bigger definition for that than most folks do.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

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Science Stuff! Credit: ScienceStuff

Wanna hear me talk about asteroids? Jorge Cham (creator of PhD Comics!) interviewed me for his Science Stuff podcast where we talk space rocks: where they come from, how we can find them, how we can keep them from hitting us, and should we mine them for valuable minerals, including water ice?

You can listen here!

Sometimes, the coolness of an astronomical image is in how it’s presented.

Sometimes also it’s the hotness. Like this image of NGC 5134, a spiral galaxy about 65 million light-years away in the constellation Virgo (not far from the bright star Spica on the sky, actually):

Fire. Credit: ESA/Webb, NASA & CSA, A. Leroy

If you guessed this was an image from JWST give yourself an infrared star [and here’s a huge 4,200 x 4,200 pixel version of it]. It is, and it’s a combination of observations taken with both its NIRCam and MIRI instruments. The Near-Infrared Camera shows mostly stars, displayed as blue, teal, and green. It’s sensitive to redder stars (red in visible light, that is, like red giants and supergiants), and you can see them blurred together into a gentle glow in the center out to the edges.

The Mid-Infrared Instrument sees longer wavelengths, and in particular the 7.7-micron filter image (displayed here as orange) selects for dust grains in the galaxy, specifically PAHs, or polycyclic aromatic hydrocarbons. These are long-chain carbon molecules very similar to soot.

I love the poetry here: the spiral arms are displayed in a way that makes them look like flames, but we’re seeing the smoke! 

PAHs are created in massive stars when they explode as supernova, and even before that when they’re red supergiants. For example, remember when Betelgeuse got really dim in 2019-20? It expelled a huge cloud of dust (a generic term that includes PAHs) that made the star appear fainter, since that dust is opaque to visible light.

But warm PAHs emit light at long infrared wavelengths, which is why this image shows them so well. Massive stars don’t live long and stay near their stellar nurseries where they were born. Those are in the spiral arms, so the dust they blow into the galaxy is in the arms as well, and this image traces that structure well. Note the brighter sections at the ends of the galaxy along the long axis; those are gigantic complexes of nebulae making stars. That’s a bit clearer in images taken in visible light, like this one by the Carnegie Observatory (the image is copyrighted so I can’t display it here, but click through to see it; it’s rotated about 90° counterclockwise from the JWST image).

Observations like this help astronomers track where stars are born, where they die, how much dust they produce, and how that affects the galactic environment. And, as always, they’re also devastatingly beautiful.

It’s funny to me; the universe doesn’t have to be beautiful, and yet it is. I think this may be coincidence; we happened to evolve an aesthetic that appreciates graceful curves, flow, and color, and those are attributes common in galaxies. But whether this is true or not, art is science, and vice-versa. I’ve been saying that for years.

Hubble Space Telescope has taken hundreds of thousands of images of the sky, many of which are “deep”, meaning long exposures that can see faint objects. The vast majority of the galaxies seen have never been seen before! That’s a big opportunity for astronomers, but how to capitalize on it?

A team of scientists decided to give this a try. They developed a neural net called AnomalyMatch to dig into the data, looking at almost 100 million (!!) cutouts of galaxies — literally, small sub-images a few dozen pixels on a side featuring a galaxy in each — to see if they could find odd-looking galaxies. These are usually the result of galactic collisions, or gravitational lensing distorting their shape. But there could be other reasons, too, so examining them on a large scale can be pretty instructive.

Neural nets are computer programs designed to look into some specific aspect of a problem where there is a large sample of data to examine. They can be trained, meaning they are fed examples of objects — in this case, weirdly shaped galaxies — then let loose on the dataset to find more. Neural nets aren’t exactly artificial intelligence, even though in a very narrow sense they can learn, but they fit the bill way better than the LLM grift going on right now.

Anyway, looking through the images the net found 1,300 objects that fit the bill [link to journal paper]. Over 600 were from galaxy mergers, 140 from lensing, 35 were “jellyfish” galaxies (galaxies moving rapidly through a galaxy cluster and having their internal gas stripped away, leaving long tendrils behind them), and two were edge-on protoplanetary disks (disks of material around young stars that planets form from — in fact, this project was first trained to look for disks, but they expanded the list as time went on).

Six galaxies from the search, including gravitational lenses and collisions. More info can be find by clicking the image. Credit: NASA, ESA, David O'Ryan (ESA), Pablo Gómez (ESA), Mahdi Zamani (ESA/Hubble)

1,300 out of 100 million is a small fraction, but imagine trying to do this yourself by eye! I imagine if they relax the parameters a bit they’d find many more, too. This was a first attempt, and shows that this sort of work is possible and helpful.

I played with neural nets a bit when I worked on Hubble — I was doing similar work looking for faint red dwarfs in the data — but found it a bit too out of my wheelhouse for me to use well. Also, those were early days of that sort of thing, and a lot of progress has been made since then. So I’m glad to see this going on! With Rubin and Roman coming online soon, we’re going to have vast amounts of data to sort through, so neural nets will become important, if not critical, tools for searching.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!

Gamma Cassiopeiae, or just Gamma Cas, is a naked-eye star easily visible from the northern hemisphere; it is the central star in the W (or M) of the iconic constellation Cassiopeia. It’s about 550 light-years from Earth, and is a whopper: it has 15 times the sun’s mass, which means it’s very luminous, about 15,000 times the sun’s energy output. Replace the sun with Gamma Cas and we’d be cooked.

It’s the powerhouse behind the glow in the weird nebula the Ghost of Cassiopeia, which I’ve written about before, too.

But it’s also been at the center of a minor mystery in astronomy that’s bedeviled astronomers for decades. That mystery has finally been solved, but let’s take a step back first to understand what’s what.

Gamma Cas (arrowed) is the center star in Cassiopeia’s W. Credit: Torsten Bronger on Wikimedia commons (CCA 3.0)

It’s a B-type star, which is a classification that means its hot and luminous. But it’s more than that: it’s a Be star (pronounced “Bee Ee”, with the letters spelled out). The “e” stands for emission. In stars like the sun, hydrogen in a star’s atmosphere absorbs light coming up from below at very specific wavelengths (colors), so that when you get a spectrum of the star (spreading its light out like a rainbow) there are dark features at those wavelengths. That’s an absorption spectrum. 

But in some stars the hydrogen is actually excited, pumped up with energy and emitting light at those wavelengths, so we get an emission spectrum. Be stars are like normal B stars but with that emission feature.

We’ve known for a long time that Be stars are rapid rotators, spinning at tremendous speeds — Gamma Cas spins at nearly 400 kilometers per second, while the sun’s rotation is only 2 km/sec! — which is so fast that material at the equator is thrown into space by the centrifugal force. That material forms a disk around the star, called a decretion disk (the opposite of an accretion disk, where material falls onto a star or other object). That’s the material responsible for the hydrogen line emission.

Because why not, here’s the Ghost of Cassiopeia nebula I mentioned above. Gamma Cas is the fiercely glowing star above it, energizing the nebula’s gas. Credit: Ryan M, used by permission

But there’s more! We also know it’s orbited by a white dwarf (called Gamma Cas Ab, making the Be star Gamma Cas Aa^* ): a star once much like the sun but which used up all its nuclear fuel, swelled into a red giant, blew off its outer layers, and revealed its hot, dense core to space. In fact, when that star became a red giant it dumped a lot of material onto Gamma Cas Aa, which is also why it spins so quickly. That material sped it up like a basketball player slapping a ball while balanced on their finger to make it spin faster. 

As it happens, the system also generates a pretty decent amount of high-energy X-rays. The source has been a mystery for decades, though! The X-rays could come from the magnetic field of the Be star interacting with the material in the decretion disk, but if matter is streaming from that disk onto the white dwarf (a reverse of the older situation) it could also generate X-rays.

It hasn’t been possible to distinguish the two scenarios until now. A team of astronomers used the Japanese (with participation from NASA and ESA) XRISM X-ray space observatory to take a look at Gamma Cas. It’s designed to take high-resolution spectra of X-ray emitting objects, which hasn’t been possible before. The importance of this is that when objects move toward or away from us, the wavelengths they emit shift to shorter or longer wavelengths — a Doppler shift. We can measure the object’s motion that way, including its speed. 

What they found is that there is a cyclic shift in the X-rays from the Gamma Cas system, and it matches the orbital period of the white dwarf (including shifting to the shorter wavelengths when the star approaches us in its orbit)! That means it must be coming from the white dwarf, and not the Be star [link to journal paper].

Artwork depicting how astronomers think Gamma Cas produces X-rays. Credit: Nazé et al. 2026

Premium subscribers let me play among the stars 

Hello, Earth
Hello, Earth
With just one hand held up high
I can blot you out, out of sight

Peek-a-boo, peek-a-boo, little Earth

 -Kate Bush 

On April 1, 2026, the crew of the Artemis II lunar mission launched into space. Today (Monday, April 6) they will swing around the far side of the moon (NOT the dark side, although in this case it mostly is due to the waning gibbous phase, but I’ll just leave that alone!) and at closest approach will be only about 6,500 kilometers from its surface. After that they’ll start to head back to Earth and are expected to splash down in the Pacific Ocean on April 11.

You probably already know this is the first crewed lunar mission in 50+ years, and a lot of firsts will be achieved during the flight. I have a lot of opinions about this mission, NASA’s plans, and the rocket itself being used, but that’s not what I want to focus on here. Instead, let’s look at something very cool indeed.

After launch, the spacecraft was in Earth orbit, a sort-of parking orbit until they were in the right position to ignite their engines for a translunar injection burn that sent them up and away from our home world and on their way to the moon. Not long after that was done, astronaut Reid Wiseman pointed a camera out the capsule window and took a truly amazing photo of Earth: 

Hello, Earth. Credit: Reid Wiseman/NASA

[Click the photo to see much higher-resolution versions where the stars and more are clearly visible.]

That’s fantastic. It spread like wildfire online, unsurprisingly, with a lot of people asking about it, curious about what they were seeing. Some of the information being shared was great, some incorrect, and some didn’t give the full picture. I’ll try to fix that!

First, this shot of Earth is not lit by the sun. So what’s lighting it up then?

The moon! It was full, and the full moon is pretty bright  — you can read by it. What you’re seeing is light from the sun reflected off the moon, hitting Earth, and reflecting back up into space where the astronauts could see it.

When this shot was taken the sun was directly behind Earth, completely blocked out. However, it wasn’t centered behind it but instead a bit closer to the lower right side as seen here — if you look that way in the photo you can see a bright sliver, a very thin crescent. That’s sunlight passing through Earth’s atmosphere and lighting it up (it’s not the actual surface being lit by the sun)! The digital camera (a Nikon D5) was set for a ¼ second exposure at f/4 with an ISO of 51,200, which makes it very sensitive to light. The moonlit Earth is therefore exposed well, but the sunlit air to the right is overexposed.

If we were looking at Earth’s dayside here, it would vastly outshine the stars, which would be completely invisible. We see stars, so this must be the night side.

Wiseman took another shot about 20 seconds later at a 1/15^th of a second exposure that makes it more clear this was taken over the unlit side:

Same as above, but Earth is much darker. Specks of light can be seen across Earth. Credit: Reid Wiseman/NASA

Cooool.

As for Earth itself, the center of the disk is over the Atlantic Ocean west of Africa, with that continent looming large to the left, dominated by the brown tones of the Sahara Desert. Just below it is Spain and Gibraltar. On the far right South America is visible through the clouds — I’m pretty sure the specks of light across the face of Earth in the shorter exposure photo are cities in South America and Africa. Note that south is up here; we’re used to seeing maps the other way around, but in space up and down are relative. I’ve seen some folks displaying this photo with north up, which I get, but I prefer it this way, how the astronauts saw it. Remember: they were in space when this was taken. It’s always good to shake up your perspective a bit.

The odd glow just above and to the right of center is very likely a reflection of light off the cabin window. If you ramp the brightness up in the photo you can see the edge of the window frame on the left of the photo, too.

Speaking of perspective, a tricky aspect of this is that they weren’t all that far from Earth when the photo was taken, so you’re not seeing the entire hemisphere. Think of it this way: the horizon is only a few kilometers away from you when you’re standing up in a relatively flat area (like a beach), so your view is limited. The higher up you go, the farther the horizon is and the more of the planet you see, and when you’re really far away (technically infinitely far away, but, say, a hundred thousand kilometers is enough) then you’re seeing essentially the entire hemisphere of the planet.

Here, they were too close to see the whole thing. Judging from the stars (which I’ll get to in a sec) Earth is roughly 45° across, so doing the trig they were about 8,500 km away (measured from Earth’s surface in the center of the image) at that moment. Enough to see a lot of the planet, but not the complete hemisphere. The camera was using a 22 mm focal length, which is a wide angle, wider than you usually see in a normal cell phone camera, for example, which is why Earth only fills about half the frame.

Sticking with Earth for a moment more, look to the top and bottom of the disk: see that green glow? That’s the aurora! It’s pretty common to see the aurora in shots taken from the ISS, but that orbits pretty low and only sees one pole at a time. Here we see both the aurora borealis (northern lights) and the aurora australis (southern lights) simultaneously!

Also, there’s a reddish-brown ring encircling the Earth at the same height as the aurora; that’s airglow: oxygen atoms energized by sunlight during the day and slowly emitting that energy in the form of light. Again, ISS photos show this all the time. It’s a thin layer of oxygen that glows this way, so it’s easiest to see when you’re looking toward the horizon from space, when your line of sight goes through the most material (called limb brightening).

Now, finally, to space. The bright “star” off the lower right edge of Earth is actually the planet Venus! I knew this right away when I first saw this shot; from the ground Venus is now appearing over the western horizon after sunset. I’ve seen it a few times through the trees this past week, and it’s slowly getting higher every night. Given the shot is looking toward the sun past Earth, I knew that had to be our evil twin planet. 

You can also see an eerie glow seemingly reaching up from Earth toward Venus. That’s an illusion; it’s actually zodiacal light, the glow of sunlight reflecting off dust released by comets, so it’s actually far in the background. It’s pretty faint and difficult to see from the ground, but much easier from space.

You can also see dozens of stars in the photo, too. Given how wide the shot is and how sensitive the camera was, when I saw the photo I knew it wouldn’t be too hard to identify them. The stars near Venus are in the constellation Pisces, with Cetus to the upper right, and Andromeda to the left (the brightish star at the 7:00 position around Earth is Alpheratz, the brightest star in Andromeda; unfortunately the Andromeda Galaxy isn’t visible which would’ve been amazing). To the upper left are the stars in Aquarius — I got a kick out of that. The Apollo 13 lunar module was named Aquarius.

I’ll note that not too long after I figured all this out I saw my friend Corey Powell posted a much more detailed annotated version on Bluesky if you’re curious (the image has been flipped in that version).

Anyway, I was able to use the positions of the stars to get a rough estimate of how big Earth appears here, and then use the small angle formula to get its distance (they were about 15,000 km from Earth’s center, so subtracting its radius of 6,400 km I get roughly 8,500 km).

All of this is amazing. And there’s so much more; NASA is posting the images as they come in from space. Today the astronauts are very close to the moon, and I’m really looking forward to seeing those shots as they’re made available. Closest approach is at 19:02 Eastern US time tonight, and NASA will be covering all of this live. You can watch on NASA TV or on their YouTube channel. I will be.

You can email me at thebadastronomer@gmail.com (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!