JWST M51 image credit: ESA/Webb, NASA & CSA, A. Adamo (Stockholm University) and the FEAST JWST team

Today — Thursday, June 20, 2024 at 20:50 UTC (4:50 p.m. Eastern US time) — is the moment of the June solstice, when the Sun reaches its most northerly point in the sky. For people in the northern hemisphere this means the amount of daylight we have is at a maximum (the day is longest), and those in the south have the longest night^*.

If you pay attention to where the Sun rises and sets along the horizon (its azimuth), today is when it rises the farthest north of east, and sets the farthest north of west. Since the December solstice the Sun has been moving northward, fastest at the equinox, but slowing ever since. Today that daily motion comes to a halt (solstice means “the Sun stands still”) and reverses itself. It will start to rise and set a little bit farther south every day, accelerating until the September equinox, then slowing again until it stops at the December solstice, and then the cycle repeats itself.

In the north, some people like to think of this as the first day of summer, though that connection is a bit dubious. It’s been hot for a while, and usually gets hottest in August, closer to the equinox. With global warming, though, all bets are off.

I’ve written about the solstices a zillion times, so if you’re interested lots more info is in the BAN archive.

Happy solstice to all those who celebrate!

^* This is why I don’t call this the “summer” solstice, since that’s unfair to southern hemisphereans. It’s winter there.

Speaking of celebrating the solstice, I realized it’s been a long time since I had a subscription sale, and what better time than when the Sun is up longest where I live, making nights short and astronomy more difficult?

Wait. That didn’t come out right. Still: sale time!

For the next week I’m cutting the price of subscribing to the Bad Astronomy Newsletter to just $4/month or $40/year.

That’s a 20% drop. When you become a Premium subscriber you still get Monday issues, but also issues on Tuesdays and Thursdays as well! That’s a lot of astronomy (and whatever else is floating around in my brain). You can also leave comments on the posts and talk about them with other subbies.

If you’re a free subscriber now (or you haven’t signed up at all yet), just go to the subscription page, enter your email, and you’ll be able to toss me coin and get yourself started.

If you’re already a subbie, I suppose you can cancel then resubscribe to get the discount rate. Bit of a pain, but I can’t retroactively apply it to people who have already signed up. Sorry about that. 

This sale ends next Thursday at 11:00 a.m. Eastern US time. Thanks!

The big solar storms in May 2024 that caused epic aurorae even at mid-latitudes had their effects not just on Earth, but on Mars as well.

The storms included explosive eruptions of high-energy subatomic particles that flew across the solar system at very nearly the speed of light. They slammed into Earth’s magnetic field and were funneled down to the poles, where they hit molecules in our air and caused them to glow.

But those storms hit Mars, too. The Red Planet doesn’t have a strong enough global magnetic field to concentrate the particles, so it doesn’t get strong, localized aurorae like we do. The thin air doesn’t stop them either, and many of these fast particles are free to get all the way to the surface… where we have quite a few robots working.

The Curiosity rover is one of them, and during that storm got slammed with zippy particles. These hit the digital detectors on board and deposited energy, registering as light. Some hit at sharp angle and affect only a few pixels, while some come in at low angle and streak across the detector. You can see them in the images!

If you click the link you’ll see animations showing the images as the particles hit, leaving salt-and-pepper tracks.