Since today is Halloween, why not show you a holiday-appropriate shot of the sky? The European Southern Observatory just released this lovely image of the Dark Wolf Nebula:

The dark nebula across the top does bear a lupine resemblance, doesn’t it? Also a horse, I think. But the line of stars across the lower jaw does look like a line of sharp teeth, and that really sells the wolf aspect.

This is actually a small section of the much, much larger Gum 55 (also called RCW 113; many objects have several catalog names) nebula, a huge region of star-forming gas toward the center of our galaxy (in that link, the Dark Wolf is at about the 9 o’clock position). When stars are born en masse, many of them will be massive beasts, a dozen or more times the mass of the Sun. These live their lives furiously and die quickly. As they do, they expand into red supergiants and blow out vast amounts of dust: dark grains of carbon and silicates. Dust is opaque to visible light, so we see it in silhouette against the brighter gas behind it.

That is a recipe ripe for pareidolia, the psychological effect of seeing familiar shapes in otherwise random or semi-random structures. Clouds in the sky are usually the culprit, but astronomy is full of them, too. I wrote about just this effect in my Halloween article for Scientific American last week, too. 

The wonderful Astronomy Picture of the Day site also has a great one of a cosmic bat, seriously one of the best I’ve ever seen of the kind. It’s super creepy. Reminds me of one of my favorite old movies, Curse of the Demon. That’s a great flick, by the way, especially if you like moody, atmospheric B&W movies. It’s on Internet Archive, but it’s been colorized.

I’ll also remind you that last year I wrote what is my favorite article for Scientific American, about lunar exploration and the werewolf problem. I had so much fun writing it! I hope you enjoy reading it.

And, of course: Happy Halloween!

Y’all know we love the web comic xkcd around these parts. It’s one of the most (or maybe the most) popular comics online, for good reason.

Sometimes, though, its creator Randall Munroe gets a little esoteric. I’ve had to look up explanations for his jokes more than once! But sometimes that narrowly targeted audience overlaps with me, which always gives me an extra kick.

I’m not sure how I missed this when it went up in January 2024:

Ha! The idea here being that a supernova, or exploding star, makes astronomers happier the closer to Earth it is (because more distant ones are fainter and harder to observe), but only up to a point; if it’s too close then there’s trouble.

That’s the immediate joke. But there’s a more subtle one.

The shape of the graph itself is the same as what we call a supernova light curve, the change in brightness of the event over time. An exploding star brightens rapidly (usually over about two weeks), peaks, and then fades more slowly, taking months to decay back to the background.

So that’s a pretty great joke. Layers!

And why not add some science: The reason for the shape of the curve has to do with what’s powering the explosion when the core of a massive star collapses, which overall is radioactive decay of elements forged in the explosion (early on it’s just the ridiculous energy released in the explosion itself, which peaks because as the debris expands it cools and doesn’t radiate as much light). Nickel-56 decaying into cobalt and iron makes incredibly energetic gamma rays that are absorbed by the debris, heating it and making it glow as well. That fades after a few months, but it slows the fading and creates the first part of that long tail to the right. Even later, radioactive titanium-44 decays and also makes gamma rays, heating the debris more slowly, and can power the light for many years.

It’s actually way more complicated than this (there’s more that one kind of supernova, in fact, which I covered in an article for Scientific American), because everything in the Universe always is, but that’s the gist. And now you know why xkcd is funny on multiple levels.

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