Catching Comet Tsuchinshan–ATLAS

Tuesday evening I drove up Maunakea to the Visitor Information Station to see if I could spot Comet C/2023 A3, a.k.a. Comet Tsuchinshan–ATLAS. I hadn't felt particularly motivated to get up before dawn to see it earlier, but now that it's in the evening sky I figured I'd see if I could spot it.

For an astronomer, I'm a little embarrassed at how few comets I've actually seen. While solar eclipses (which I actually have never seen) either land in very out-of-the-way places or come at inconvenient times when I'm scrambling not to spend money on travel, I haven't lacked for chances over the past few decades to see comets (though a few, like Comet NEOWISE in 2020, did come at times when I wasn't really able to get somewhere dark enough to see them). Still, I don't have much excuse for missing Comet McNaught in 2007 or Comet Lovejoy in 2011. I did see Comet Holmes' remarkable brightening in 2007, though that was an unusual comet since we were seeing it almost head-on, so it didn't really display much of a tail. There are probably a few more I missed in that time span as well which I've forgotten; on the whole, I have a pretty poor track record of seeing naked-eye comets even when presented with the opportunity.

Which is why I found myself yesterday trudging up the path to the top of Puʻu Kalepeamoa in some extremely strong (and frigid) winds, setting up my GoPro for a timelapse, and waiting for the sunset. The timelapse didn't quite work out as planned since it failed to adjust the exposure time properly after it got dark, but I managed to get some photos, at least. 

The setting Sun through a māmane tree. They're in bloom this time of year.

The nearly-full Moon, unfortunately, wasn't doing the comet any favors as it lit up the night sky. I was first able to make it out maybe a half hour after sunset, then as twilight faded it became easily visible for perhaps another hour or so; by the time I left, nearly two hours after sunset, it was getting low enough on the horizon to be difficult to make out again.

Comet Tsuchinshan-ATLAS over Hualālai, with Venus at left.

With that, I can finally say that I've seen a proper, honest-to-goodness hairy star, and I have the pictures to prove it. Speaking of, I got those shots with my Pixel 7 Pro; not as good as a professional camera, but it's still remarkable to me just how good the software and hardware in phones has gotten, that it can capture shots like this in low light. (I did set it up on a tripod for stability, but still.)

Overall it was an interesting experience, and I'm glad I made the effort to see it. (Though after sitting out in those winds, maybe I should've gotten up to see it before dawn from Hilo, where it'd be warm[er] and humid instead of frigid and parched…) It should still be visible for a little while, perhaps the next few weeks; the Moon will start rising later and it'll be getting higher above the horizon, which will both make it easier to see, but it's also receding from the Sun which will make it get fainter, so there's a tension between the various effects. The next few days should still be good, though, and I'd recommend making the effort if you haven't seen it. I probably won't head up Maunakea again, but I'll try to keep an eye out for it from Hilo as it rises high enough now to be seen above the western horizon. A hui hou!

Happy half-birthday, Halley's comet!

I'm typing this on my lunch break at work so this'll be short, but this week I learned that Halley's comet will reach aphelion, the farthest point in its orbit from the Sun, at 3 PM HST (when this post goes out). At that point it'll be momentarily traveling at its slowest speed (relative to the Sun), a mere 0.91 km/s, or 2,035 mph. After that, it begins the long accelerating fall back in towards the inner Solar System. And yes, aphelion is only a "half-birthday" if you count its "birthday" as being perihelion, but it's as good a time as any and makes for a catchy title, so I went with it.

Halley's comet (or 1P/Halley to give it its official designation, the "P" meaning "periodic" and the "1" meaning it's the first to be recognized as such) is currently far too faint to be observed from Earth with even the largest telescopes, having last been imaged twenty years ago in 2003. (It might be possible to observe with the Hubble or JWST, but no one is looking – there wouldn't be much to learn from it.) Presumably that means it'll take about another twenty years to be imaged again, so look forward to that sometime around 2043, unless the ELT decides to try for it earlier or something.

Having been born three years after its most recent perihelion in 1986 I've never seen Halley's comet myself, but this is a nice reminder that it's still out there, and on its way back in again. Hopefully I'll get to see it at its next perihelion in July 2061! A hui hou!

Making a Comet

This past week I took part in Journey through the Universe for the second time. Journey through the Universe is an annual event, running for the past eleven years, where astronomers and engineers from the various observatories on Mauna Kea go into classrooms and give talks to the students there. Most of the time these talks include some sort of physical demonstration or hands-on activity. This year I talked about comets, and as part of my talk I created a miniature comet.

Comets are basically, in the immortal words of Fred Whipple, “dirty snowballs.” They are composed of varying amounts of rock, dust, and various ices such as water, carbon dioxide, and ammonia. In preparation for my presentation I did a few test runs of the comet-making recipe I found, including two at work which proved quite popular with my coworkers. I took some pictures of the process (though in poor light, unfortunately) and thought I'd share them here.

We start with a plastic garbage bag inside a large plastic mixing bowl. (When dealing with dry ice, you really want to keep it away from metal as the extremely fast cooling of the metal causes it to emit nails-on-a-chalkboard-level screeches.)

Next, we add some dirt and stir it in.

Then, we add a dash of ammonia and some corn syrup, to represent the assorted organic molecules detected in comets. Organic, in this context, is used in the chemistry sense, meaning “a molecule containing carbon.”

Now, we crush up two cups of dry ice by pounding it with a meat tenderizer, add it to the dirty water, and stir vigorously. This produces an impressive amount of fog, making it hard to see what's happening, but you can feel the ice start to freeze up pretty quickly.

When it's mostly frozen, you can pick up the bag and form the comet like a snowball (something I have basically zero experience doing, I should note). When that's done, we've got a comet!

(Man, that light is poor.)

I don't usually take pictures of myself, so this actually took quite a bit of practice, and I got a bunch of melting dirty comet-water on my hand and a cramp in my leg in the process. Here's a close-up look at the comet:

This comet may actually be the best one I've made so far. I initially thought some of the chunks of dry ice were too big, but thinking about it now I think that may actually be a good representation of real comets. After making the comet I stuck it in a pan in front of me on my computer desk and watched it as it melted over the course of a few hours. This last picture was taken about half an hour after making the comet, and show pits where the water ice froze around some dry ice which has now melted, leaving a pitted surface.

This is quite a fun project to do. The part where you mix the dry ice and water is especially visually impressive, and quite popular with bystanders. You'll most likely have dry ice leftover, too, so you can have more fun with it after the fascination of watching a comet melt has worn off. A hui hou!