Comet C2020 F3 NEOWISE in the Morning (and eventually, the evening) (Shallow Thoughts)

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sat, 11 Jul 2020

Comet C2020 F3 NEOWISE in the Morning (and eventually, the evening)

[Comet C2020F3 NEOWISE over California desert landscape, by Dbot3000]
Comet C2020F3 NEOWISE over California desert landscape. Photo by Dbot3000

I've learned not to get excited when I read about a new comet. They're so often a disappointment. That goes double for comets in the morning sky: I need a darned good reason to get up before dawn.

But the chatter among astronomers about the current comet, C2020 F3 NEOWISE, has been different. So when I found myself awake at 4 am, I grabbed some binoculars and went out on the deck to look.

And I was glad I did. NEOWISE is by far the best comet I've seen since Hale-Bopp. Which is not to say it's in Hale-Bopp's class -- certainly not. But it's easily visible to the unaided eye, with a substantial several-degree-long tail. Even in dawn twilight. Even with a bright moon. It's beautiful!

Update: the morning after I wrote that, I did get a photo, though it's not nearly as good as Dbot3000's that's shown here.

I've seen the comet several mornings in a row (I haven't been sleeping well, so I keep waking up at times that would normally be annoying but right now are perfect for comet watching). I haven't gotten a photo of it, though, so here's a photo from Dbot3000 on Wikimedia Commons.

An even better photo was today's APOD, The Tails of Comet NEOWISE. The two tails aren't as striking as Hale-Bopp's were, but they're still remarkably beautiful, with some nice color contrast, in a long-exposure photograph like the one in the APOD. I can't wait to see it in skies that are actually dark.

Finding Comet NEOWISE

Comet NEOWISE is in the northern sky, on the northeast end of Auriga. Find Capella between 4:15 and 5 am, and slide your view down to the horizon and a little left, and you'll see it.

Or, if you aren't familiar with Capella, just look a little north of due northwest, just above the horizon. Use binoculars if you have them, or a small, wide-field scope, but you don't strictly need any visual aids.

What about this inconvenient morning timing? Well, the comet is moving northward, which means that it will start becoming visible in the evening sky soon. It's not far enough north to be circumpolar (visible all night) for most people, but it is far enough north that for a while we'll be able to see it in both the morning and evening skies on the same day.

When? That's unclear. Right now, from here in New Mexico (latitude about 36), the comet sets in the evening at about 9:40 pm daylight time, and rises in the morning at about 3:44. I suspect that it might be possible - barely - for someone with a very good horizon to the northwest to see the comet at around 9:30. I have the Jemez mountains in that direction, so the comet sets a bit earlier and there's still too much light to see it.

But it's moving fast and should change rapidly. How fast? Well, I was having trouble finding websites that would answer that question, or getting the answer from planetarium programs except by bumping one day forward, checking the rise/set times, going back to the Time menu to bump it another day, repeat. What a pain. Automating problems like that are what computers are supposed to be for.

Scripting it with Skyfield

The easiest way to generate a table of rise/set times turned out to be Skyfield, a Python library by the author of the excellent PyEphem, and meant to replace PyEphem. As I was searching for solutions, I discovered by accident that just a couple of days ago (I'm guessing this was related to the comet), there was a new update of Skyfield adding a long-requested feature to download orbital elements for comets and asteroids. And they did a great job. The documentation is very clear and the API is well designed to make downloading orbital elements much easier than it is in most packages.

It still took me most of a day to script everything I wanted, mostly because date and time problems in astronomy programs always turn out to have hydra heads; but now I have comet.py to give me a table of rise and set times.

Here they are for White Rock, NM:

$  ./comet.py -d 5 -c 35.8 -106.2 -e 1980 '2020 F3'
C/2020 F3 (NEOWISE)      2020-07-11 16:40 MDT
RA 06h 55m 39.45s    DEC +43deg 11' 10.9"    Distance 0.868955 au

Observer at 35deg 48' 00.0" N   -106deg 12' 00.0" E   Elevation 1980.0 m
Altitude 44deg 04' 40.4"      Azumuth 298deg 23' 50.9" 0.868925 au

Rises and sets over 5 days:
  2020-07-11 21:40 MDT Set    Aziumuth 328deg 44' 27.5"  Dist 0.862762 au
  2020-07-12 03:44 MDT Rise   Aziumuth 30deg 41' 15.6"   Dist 0.855333 au
  2020-07-12 22:00 MDT Set    Aziumuth 330deg 59' 04.5"  Dist 0.833811 au
  2020-07-13 03:44 MDT Rise   Aziumuth 28deg 30' 25.4"   Dist 0.827303 au
  2020-07-13 22:21 MDT Set    Aziumuth 333deg 04' 04.0"  Dist 0.807095 au
  2020-07-14 03:46 MDT Rise   Aziumuth 26deg 29' 58.5"   Dist 0.801481 au
  2020-07-14 22:44 MDT Set    Aziumuth 334deg 54' 01.8"  Dist 0.782819 au
  2020-07-15 03:51 MDT Rise   Aziumuth 24deg 45' 23.8"   Dist 0.778043 au
  2020-07-15 23:06 MDT Set    Aziumuth 336deg 22' 05.6"  Dist 0.761163 au
  2020-07-16 03:59 MDT Rise   Aziumuth 23deg 23' 34.8"   Dist 0.757152 au

The morning rise time isn't changing much, but the evening set time is changing fast: 9:40 pm tonight, to 10 tomorrow night, to 10:21 Monday night. I'm optimistic that even if I can't find it tonight, it'll be high enough tomorrow night that I'll be able to see it, and it should only get better from there.

NEOWISE, by the way, gets its name because it was discovered by the Wide-field Infrared Survey Explorer space telescope, originally launched in 2009 as plain old WISE, and then reactivated in 2013 as the Near-Earth Object WISE.

So check it out! It's not often that we get a chance to see a comet that actually looks like a comet. If you happen to find yourself awake between 4 and 5 am, look to your northeast horizon. But if that's too early for you just wait a few days, and keep watching the northwestern sky as evening twilight descends.

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[ 18:18 Jul 11, 2020    More science/astro | permalink to this entry | comments ]