I’ve mentioned a few times here that I write a biweekly column for Sen.com, a site that has lots of news and blogs dealing with space exploration (Sen stands for “Space Exploration Network”). The news articles are free, but the blogs are subscription only.

My latest article there is one I’ve been meaning to write for some time: What phenomenon sculpted this weird pair of craters, each with a central pit in it? It turns out the answer is … layered.

Sen.com is worth the subscription price. There are a lot of good writers there, including my friends Emily Lakdawalla, Chris Lintott, and many more. Go check it out!

I’m really pleased to see so many people and organizations doing what they can to inspire young girls to take up STEM (science, technology, engineering, and math) paths in school. Women are still severely underrepresented in those fields. It’s a complicated situation—endemic sexism at the professional level, unconscious bias about teaching girls at the grade-school level, and everything in between—but one thing that I think will help is raising awareness and making sure there’s a positive, supportive atmosphere out there.

That’s why I’m very pleased that my good friends, the Scirens—Taryn O’Neill, Gia Mora, Christina Ochoa, and Tamara Krinsky—have created a short video in honor of International Women’s Day to help girls get into STEM.

The Scirens are four actresses who love science and are great science communicators. They do a lot of outreach, getting science out to the public in clever ways. They have Science Soirées, private but very informal get-togethers with a scientist speaker and a curious audience of people who are free to ask questions and spark conversations. Christina (as part of the Nerd Brigade) helps organize science Q&A sessions at the L.A. Natural History Museum as part of First Friday there (I was just at one last week and it was really great; lots of people attended and were clearly loving it). Gia has a one-woman cabaret act called “Einstein’s Girl,” an allegory of physics and love, and it’s really good (I saw it last year in Denver). And lots more.

Having role models is important. A lot of the time, kids don’t see people like themselves on TV, in movies, or online, and that is certainly true for girls when it comes to science. We’re doing a lot better with that now, but that doesn’t mean we can relax. We need to keep making sure this message gets out, and making it even more diverse and inclusive, so that anyone, everyone, can feel that they can choose to pursue a STEM career if they want to.

Realistically, that will take a long time and will involve a lot of work and broadening of our efforts. But we’re facing the right way, we’re moving in the right direction, and every time we make that path easier, we all win.

Update (Mar. 10 at 20:00 UTC): To be clear, the Scirens don't officially do the Q&A sessions at the LA Museum; Christina does that and she is part of both Scirens and the Nerd Brigade.

I am very pleased to announce a new video series I’m doing! My Benevolent Overlords here at Slate and I are producing a weekly news-ish astronomy video called—and this was their idea—“Bad Astronomy.” The plan is to put out one every Monday based on a recent bit of cosmic news (usually but not necessarily based on something I’ve written about in the past week or so).

Here's the first episode: “How to Survive a Close Encounter With a Monster Black Hole”:

This episode was based on an article I wrote late last year. Jim Festante at Slate did a great job putting the video together—I’ve done some video editing on my own, and it’s some form of magic I could never quite grasp. I’m really happy Jim's doing all the heavy lifting in that area; the graphics are great! Jeffrey Bloomer edits the script, too.

This was fun to work on (literally: I record the audio with a blanket over my head to reduce echo, so it’s like being in a pillow fort, though with less ventilation). And I’ll add that this is all part of an experiment (together with Crash Course Astronomy, my column for Sen.com, and another secret project I’m just looking into right now) to see if I can squeeze 25 hours of work into a day.

I’ll let you know. Maybe I can move to Mars; that’ll buy me an extra half hour.

Anyway, let me know what you think! And stay tuned. Another one is coming your way next week.

Astronomers marked a milestone last week when they observed a supernova, an exploding star, halfway across the Universe. We see these all the time, but the reason this particular one is significant is, literally a twisted tale.

First, here’s the extremely cool image of the supernova:

That’s a Hubble Space Telescope shot, part of a much larger image showing a cluster of galaxies over 5 billion light-years distant. Almost everything in this picture is a galaxy (the very bright cross-haired object is a star in the foreground, in our own galaxy).

The central part of the picture is magnified in the inset, and the star is indicated by arrows. But wait a sec. Why are there four arrows?

Because each of those is an image of the exploding star! The light from the star traveled for billions of years to get here, and on its way here the road split. More than once.

Here’s how that works. The star is in a spiral galaxy well over 9 billion light-years from Earth. It exploded, sending light out in all directions. On its way to Earth, some of that light passed through the galaxy cluster. The gravity of that cluster is immense (due to the mass of stars and gas in it, as well as lots of dark matter), and it warps space. As the light from the supernova moved through the cluster, it followed that bending of space; twisting and turning with it. That alone would be enough to distort the image of the supernova and its host galaxy.

But then there was an added surprise: Some of that light passed very close to a massive elliptical galaxy in the cluster. That strongly warped the light, bending it such that we get multiple images of the star. Think of it this way: As you look at the image, some of the supernova’s light was heading off to the left of the galaxy, and if it had kept going that way would’ve missed Earth, and we’d see nothing, but the galaxy’s mass bent the light’s path, aiming it toward us. The actual details are quite complicated, but this can create multiple images of a single object; in this case four of them.

We call this effect gravitational lensing (I’ve written about it multiple times—haha—like here, here, here, and here, and you should click those for more info as well as awesomely cool images of lensing), and it was predicted by Einstein under his theory of relativity. We’ve seen it many times, but never before has a supernova been under such a lens. This is a first.

It gets better. The light gets magnified, so that we can see the supernova more easily; in this case it’s about 30 times brighter than it would have been without lensing. And there’s yet another benefit: Because the light has taken different paths to get to Earth, we see time delays between each.

Actually, the Hubble site has a great analogy for this:

The supernova's various light paths are analogous to several trains that leave a station at the same time, all traveling at the same speed and bound for the same location. Each train, however, takes a different route, and the distance for each route is not the same. Some trains travel over hills. Others go through valleys, and still others chug around mountains. Because the trains travel over different track lengths across different terrain, they do not arrive at their destination at the same time. Similarly, the supernova images do not appear at the same time because some of the light is delayed by traveling around bends created by the gravity of dense dark matter in the intervening galaxy cluster.

Cool, huh? Interestingly, in the big picture of the cluster, you can actually spot at least two other images of the star’s host spiral galaxy; the galaxy light was lensed and multiplied too. It’s bizarre, but extremely useful to astronomers. The amount of bending and the time delays involved provide a way to measure how much mass is in the cluster, how it’s distributed, and also how fast the Universe itself is expanding! That last part comes out because of the great difference in distances between the supernova and the cluster; the expansion of the Universe affects how the light travels between them and to us, so measuring the delays gives us another way to measure the cosmic expansion.

Models of the cluster made by the astronomers who made this discovery indicate that other images of the galaxy may come from paths that are taking longer to get to Earth, so in them we still see the galaxy before the supernova went off. That means in a few years we may get to see the explosion rise again, as if the Universe itself were set on rewind. That’s a very rare opportunity; to know when and where a star will explode!

I find this all quite delightful. The distant Universe is extremely difficult to study because, duh, it’s far away. Things are small and faint. Gravitational lensing allows us a chance to take a narrow but deep slice of that distant realm, and see it better than we could have before. It’s a happy circumstance that astronomers are all too thrilled to capitalize upon.

A couple of weeks ago, the interplay of the inexorable dance of gravity and the perspective brought by geometry combined to bring three celestial objects together: Venus, Mars, and the Moon. They all appeared very close together, in an event technically called an appulse, but what most people more casually call a conjunction.

Unfortunately it was cloudy and/or snowing here in Colorado, so I couldn’t see it for myself, but people from all over the world took pictures and posted them to Twitter and Facebook. That was nice; if I couldn’t see it for myself, at least I could see it through the eyes and lenses of others.

Astrophotographer Jeff Sullivan (who has contributed many amazing photos and videos to this blog) realized he could get dramatic footage of them setting behind Mount Whitney in Northern California if he went to Lone Pine. Oh, he was very right. This animation is short, but oh so lovely:

Venus is the brighter of the two “stars” to the lower left, with Mars just above it. Venus orbits the Sun closer than Earth, and is currently about as far from the Sun as it can be in our sky. It’s swinging around its orbit and headed to get between us and the Sun in August.

Mars, on the other hand, orbits farther out, and was on the far side of its orbit. During this encounter Venus was about 210 million kilometers from Earth, and Mars was closer to 330 million. The Moon was a mere 359,000 km away (measured from the centers of the Moon and Earth). It was very nearly between us and the Sun, making it a thin crescent. Note the Earthshine, the "dark" side of the Moon softly illuminated by light from the Earth itself.

The night before this happened wasn’t as cloudy here, and I could see Mars and Venus just a degree or so apart over the Rockies. As they slowly sank to the west after sunset, I could visualize their orbits in the sky, projecting their motions in my mind’s eye as the enormous virtual gears of the Universe turned and interlocked.

That to me is one of the most profound and wonderful things about viewing the sky: The utter inevitability of the motions of celestial objects; knowing that, with keen enough observations and a grasp of the math, this event could have been predicted millennia ago, and would have occurred right on time.

Here at BA HQ we’re all about weird clouds. Well, maybe not all about them, but certainly a lot about them. You’d think that clouds wouldn’t be terribly surprising (unless you’re trying to just get some Sun on a beach in Brazil) since, after all, they’re clouds. But you’d be wrong.

For example, get an eyeful of this.

Whoa. What is that?

It’s called a fallstreak or hole punch cloud. That’s not really an official name, since this isn’t actually a separate type of cloud; it’s actually something that happens to a cloud.

Here’s how this works: If you get water cold enough, it’ll freeze (duh). But, water needs something to freeze around, a particle of dust or an existing ice crystal or some other such object that can trigger the formation of ice crystals.  If you have very pure water in a very smooth container, you can slowly lower its temperature to below freezing, and it’ll stay a liquid unless there’s something that disturbs it. Water like this is said to be supercooled.

These conditions can occur in a cloud, with water floating around below the freezing point but unable to make ice. If something happens to trigger ice formation—maybe an airplane going through the cloud creating ice crystals, or dust getting into the cloud—the water will rapidly freeze around these “condensation nuclei.” The resulting crystals will then fall, leaving behind a hole in the cloud.

The fallstreak cloud above was photographed by Zora Fernandez in British Columbia at sunrise in late February. The colors are from the reddish Sun lighting up what looks to me like a nice, stable layer of altocumulus perlucidus clouds (a term I just learned and which, c'mon, is really cool). Something must have happened to trigger the fallstreak; the water then crystallized, began to fall, and voilà. Awesomeness.

Note the dark shadow across the red clouds; that’s the shadow of the fallstreak cloud on them. As the crystals fell, the low Sun cast the shadow upwards, on to the cloud layer. And the greenish color you see is most likely actually just the sky seen through the hole in the cloud layer! The odd color is probably a combination of the sky color at sunrise and the red clouds, giving it a greenish or turquoise cast.

Here’s a second shot of it:

The shadow is more obvious in this one, and the sky is paler. I’ve seen fallstreak clouds a few times. The first time I remember well; I was driving home from school in Michigan and a big one appeared out my side window. I stopped and took a picture (which I’m sure I still have, if I could dig through the bazillion prints I keep in shoeboxes in my attic; this was in the 1980s). It was so odd; the feathery icy cloud that fell left a hole in the upper layer the same shape, like a cartoon character does when they run through a wall. Freaky.

Anyway, this goes to show you: You might take the sky for granted, but it’s actually an endless show put on for free. Wanna see it? Look up.

Tip o’ the cumulus to Jenn Laycock and Nathan Santo Domingo.

I’m fascinated by tides. Not so much the movement of the ocean, as you might think. That’s a product of tides; what I mean is the change of gravity over distance stretching things.

Say what?

Let me explain. In fact, let me explain in the latest episode of Crash Course Astronomy: Tides!

This episode was one I was looking forward to writing ever since Hank Green asked me to do the series. Tides affect everything! The length of the day, the Moon always showing one face to us, the Moon’s recession from the Earth, and yes, even the oceans’ rise and fall. These are all due to a series of interlocked steps in physical logic that starts with the simple fact that gravity gets weaker with distance. Start with that, and the rest is inevitable.

Tides affect stars orbiting each other, galaxies when they collide, and even black holes as they gobble down matter. That’s so cool!

I know the idea that the Earth has two tidal bulges confuses a lot of people, so hopefully my explanation in the video makes it clear why they both exist, and not just one bulge pointing toward the Moon. There are a lot of ways to explain this; the actual vector analysis in a nonrotating frame is the best way, but I opted not to get into that in this short, basic video. Duh.

Also? I love the graphics Thought Café did for this episode, especially the one at the very, very end. This article I wrote may help you get that joke. There is, after all, a tide in the affairs of men.

P.S. Yes, of course I’ve read Shakespeare. His work has a lot of astronomical overlap.

Correction, March 6, 2015, at 14:45 UTC: I originally misstated that this was Episode 7. Sorry about that; I forgot to correct for time dilation.

Right now, in the night sky just after sunset, you have a chance to see three alien worlds at the same time.

Venus and Uranus are currently undergoing a close encounter; tonight (March 5) they’ll be a little over a degree apart, just about three times the width of the full Moon on the sky. Below them, not far away (maybe 10° or so) is red Mars.

To see them look to the west after sunset. It’s best to wait a few minutes for the sky to get dark. Venus is pretty obvious; it’s the third brightest natural object in the sky (after the Sun and Moon). Mars is still fairly bright and easy to spot below it. Uranus, though, is just on the edge of visibility to the naked eye even from dark sites, so you’ll probably need binoculars to spot it. I found it really easy to see last night using mine.

Speaking of last night, the picture above shows Venus and Uranus when I went out to observe. In the photo, Venus is overexposed and Uranus is the dot below it. You can see that Uranus is a bluish-green, too! That’s cool. Venus is a smaller planet, but far closer—about 200 million kilometers away versus Uranus’ 3.1 billion km distance. All told, in the sky Venus looks about 10,000 times brighter than its more distant cousin. Mars, incidentally, is about 340 million km away right now. It’s also smaller than Venus, so looks dimmer, too.

All three were easily visible even in short exposures with my camera (a Canon T4i using a 55-250 mm zoom). Here’s a nice shot I got last night:

It’s a 10-second exposure, so you can see some trailing in the stars and planets due to Earth’s rotation. But Venus and Uranus are visible to the upper left, Mars below them near the bottom of the frame, and a few of the brighter stars in the constellation of Pisces. If you have a camera, give it a shot! I literally propped mine up on a table and just took a bunch of exposures at different settings. It was also -14 C out, so don’t complain.

And hey—if you count the tree in the foreground, then you can see four planets in that picture! Not bad for a quick and dirty (and cold) photo session.

I hope you have clear skies tonight. This is a pretty nice scene to see. And when you’re done, turn around! The Moon rises around 6:30 p.m. local time, with Jupiter high above it, and the bright star Regulus (in Leo) between them.

The show is all over the sky. Go look!

I do love an edge-on spiral galaxy. They look so odd!

That image above is from the Hubble Space Telescope and shows NGC 7814, a galaxy about 40 million light-years away. That makes it relatively close as galaxies go! It’s a bit like looking at a house in the next town over. Not really your neighborhood, but not a long haul, either.

The glow you see is the combined light from countless billions of stars, for the most part orbiting the center of the galaxy in a flat disk. It’s not perfectly flat, obviously; you can see it’s puffed up a bit toward the center. That’s normal for spirals; they tend to have a bulge in the middle. Don’t we all.

The dark stuff is what astronomers call dust; complex molecules loaded with carbon. If you like technical terms, it’s also called polycyclic aromatic hydrocarbon. So there you go.

Dust is created when stars are born and when they die; it gets strewn through the flat disk of a spiral, but is also clumped up in knots and filigrees in giant nebulae, clouds that are stellar nurseries.

Dust is opaque, blocking starlight behind it, so when you see a galaxy like this edge on you see it as a thin line bifurcating the galaxy’s equator. NGC 7814 is a fine example of it.

When I see galaxies like this, I sometimes wonder what they would look like if we could see them from a different angle. That’s not possible; we’d have to travel millions of light-years (quintillions of kilometers!) to change our perspective. But … sometimes nature provides. There are, after all, a lot of galaxies in the sky, tipped at all different angles. Finding one that gives us a better angle isn’t that hard.

That’s NGC 6861, also as seen by Hubble. It’s a galaxy similar to NGC 7814, but obviously tipped to our line of sight. Here you can see the dust swirling around the center, as well as the glow of stars. It looks like a spiral, but in fact NGC 6861 is what’s called a lenticular (lens-shaped) galaxy, a sort-of hybrid between a spiral and elliptical galaxy. It has features of both, and may be the result of a collision between two midsize galaxies. NGC 6861 is in a small, tight group of galaxies, so a collision and merger between two of them isn’t far-fetched.

I love the picture; it looks like a flying saucer whizzing by. And it shows an effect I really love: See how the dust looks darker on one side than the other? The galaxy is relatively flat, and we see the dust on the near side (upper left) fairly directly. But there are lots of stars in the galaxy, and we look through them to see the far side; they’re between us and the far side, so we see their glow. This “fills in” the dark dust, making it look somewhat faded compared with the dust on the galaxy’s near side.

This is a pretty common phenomenon in slightly tilted disk galaxies; check out NGC 3521, NGC 7049, and NGC 2841 (seriously: Click those links. The images are spectacular). 

In a lot of objects it can be pretty hard to tell which side is which, but in these cases a little thought shows the way. Studying galaxies is a funny occupation. You can spend a lot of time learning all about one in particular, but you’re stuck with the way it appears. You can’t go there or change your perspective. But you can learn so much more by studying some of the thousands of other galaxies in the sky, comparing and contrasting.

And of course, they teach us about our own galaxy, the Milky Way. After all, we live in its disk, so we see it edge on as well, even as we’re embedded in it. That makes it both the easiest and hardest galaxy to study; we can see it up close, but it’s maddeningly difficult to understand it as a whole. By studying other galaxies, separated from us by such unimaginable gulfs, we wind up getting a better grasp of, quite literally, where we live.