Oct 29, 2019: The interstellar comet 2I/Borisov

Michael Richmond
Oct 30, 2019

Early on the morning of Oct 28/29, 2019, through rather humid skies, I attempted to detect the second interstellar object known to have entered our solar system: 2I/Borisov. Did I succeed? Well, judge for yourself: the animation below shows three pictures in a loop. Can you spot a very slowly moving, faint, smudge-like object? Don't be distracted by the big satellite trail in the final image.

North is up, East to the left, field of view 18x18 arcminutes.

The answer will be shown further down this page ...

2I/Borisov

This object is currently the subject of study by many astronomers. It's relatively faint, and not very close to the Earth, so our small telescopes at the RIT Observatory would have a very hard time making good quantitative measurements. My goal for this morning was simply to DETECT the object -- I'd never seen an interstellar visitor before!

I used the JPL Horizons ephemeris service to look up the position and brightness of the object just before dawn on the morning of 2019 Oct 29. Here's a portion of the table provided by Horizons:

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• clear filter
• images binned 2x2
• focus without filter at 0.746, FWHM = 3.2 pixel
• camera ran at T = -20 C

Notes from the night:

• no Moon, but lots of humidity. The sky was not very dark
• I re-aligned both of the finder telescopes attached to the 12-inch. They had been knocked slightly askew by a big ladder when we were fixing the dome issue.
• the comet was not far from the bright star Regulus. I noticed that Regulus (and the comet's field) were both up above the big pine tree to the East at 5:30 AM local time.
• I made a bad mistake by unplugging the guide camera while MaximDL was still running, taking a set of dark frames. The program hung, and even after I killed it, a process was still running. I had to both reboot the computer, and unplug/replug the cameras, in order to bring MaximDL back into a good state.
• temperatures were warmish: T = 50 F/10 C around 4:50 AM.

My images were taken close to 6:00 AM EST, which corresponds to 10:00 UT. Note the relatively faint magnitude estimate of 16.9. I used no filter and took a series of 5 x 30 seconds exposures:

• set C: starting at 5:54 AM
• set D: starting at 5:57 AM
• set E: starting at 6:00 AM

The final image in set E was slightly affected by clouds, so I discarded it.

I wasn't really able to find the comet in any of individual 30-second images, so I stacked the pictures in each set to create a single 150-second composite. Since the comet was moving by an appreciable amount during the images (a bit more than 1 arcsecond per minute), I found that using the SUM of the worked better than a MEDIAN combination.

This brought the object into view, barely. Below is a copy of the animation with 2I/Borisov circled:

North is up, East to the left, field of view 18x18 arcminutes.

Hooray! An interstellar comet!

Last modified 10/30/2019 by MWR.