An aurora promise, and a gorgeous red and blue galaxy

Hopefully we haven’t seen the end of the sky lighting up, plus a cool galaxy with some color, too

May 14, 2024 Issue #721

Over Your Head

There’s a lot of cosmos up there. Let’s take a look at it!

Unless you’ve lived on another planet the past few days, you’ve heard about the amazing aurora display that blessed a lot of the planet over the weekend.

Or, maybe, you lived where I do. My wife and I hopped in the car and drove a bit to get away from town lights to our north, but didn’t see anything. It was too hazy and partly cloudy, dangit.

But a lot of folks saw incredible displays, and I’m honestly happy for them. I did get to see a couple of brightish satellites moving at right angles to each other as they passed below the bowl of the Big Dipper, though, which was cool. Not aurora cool, but still cool.

A shot of the dark sky. The Big Dipper can be seen, and many faint stars, along with two short slightly wiggly trails of light nearly perpendicular to each other from the satellites.

I didn’t see any aurora, but I did get this shot on my camera of the Big Dipper, and two satellites (at the bottom) moving in almost perpendicular orbits. It’s shaky, I know, but still, I took this while holding the phone in my hand. No tripod, no support, and yet very faint stars are visible. Amazing what the new phone tech can do. Credit: Phil Plait


Anyway, I got a lot of question about the aurora, including how it works, why they show the colors they do, and so on. I’ve written about aurorae many times back on the SYFY blog, but a lot of those articles got messed up when they did some CMS upgrade years ago, and some others have been deleted in the never-ending (and self-defeating and IMO very damaging) chase of SEO.

So linking to them isn’t hugely useful anymore (you can search for them if you’d like). But I wonder.

All this activity is linked to the Sun’s magnetic cycle, which peaks every 11 years or so, and we’re very near this cycle’s peak now. That means we’re likely to get more storms, and more aurorae, though there’s no guarantee we’ll get a repeat of last week.

Point is, there’s time to talk about this, so maybe what I’ll do is write a series of articles about all this — the Sun’s cycle, the storms, why we get aurorae, and why they look the way they do — over the next couple of weeks. I didn’t have time to get it into yesterday or today’s newsletter, but maybe I can have something written before the next solar outburst. I’ll note I did write about big storms for Scientific American, but even then I couldn’t go into it at the depth I wanted due to lack of space. So all this is a) an excuse to say I couldn’t get to it in time, and 2) a fuzzy promise that I will soon.

Pic o’ the Letter

A cool or lovely or mind-bending astronomical image/video with a description so you can grok it


A spiral galaxy with wide open arms appears blue to the upper left but red to the lower right as dust blocks the view.

The spiral galaxy IC 4633 seen by Hubble. Credit: ESA/Hubble & NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA
Acknowledgement: L. Shatz


When I first saw this Hubble Space Telescope image of the glorious spiral galaxy IC 4633 I was thrown for a moment. I’ve written many times about dust in galaxies; how massive stars blow off huge clouds of teeny grains of silica and carbon, or how even more is made when stars like that explode. This material is opaque to visible light, so if it’s thick enough (like, many light-years deep depending on the density of the grains in space) it can completely block objects behind it. 

I’ve also written about how you can sometimes use dust in a spiral galaxy to determine which side of the galaxy is closer to you and which farther; dust on the near side blocks starlight from the far side, and this can be pretty obvious in some cases. 

When I saw the IC 4633 image I immediately thought, oh look, the lower right hand side is farther from us, since it’s clearly being blocked by dust. The reddish hue is a giveaway; the dust particles block and scatter away blue light, leaving only redder light to pass through. 

But then I took a closer look and realized that couldn’t be right. The dust seemed to extend beyond the galaxy, into intergalactic space… and that’s when I smiled, realizing what I was actually seeing, and the short article about the galaxy on the ESA Hubble site confirmed it: the dust was a cloud in our own galaxy, the Milky Way, and we were looking past and through it to see IC 4633. In fact that dust is only a few hundred light-years form Earth, while the spiral is 100 million light-years distant. This is like looking out a slightly dirty window to see the stars beyond.

Then I made a second bad assumpion!

Subscribe to Premium Membership to read the rest.

Become a paying subscriber of Premium Membership to get access to this post and other subscriber-only content.

Already a paying subscriber? Sign In

A subscription gets you:
Three (3!) issues per week, not just one
Full access to the BAN archives
Leave comment on articles (ask questions, talk to other subscribers, etc.)

Join the conversation

or to participate.