Comet 103P Hartley, discovered in 1986 has been receiving a bit of attention lately. NASA’s Deep Impact space probe will be making a visit in early November. However, riding around magnitude 7, 103P Hartley is now easily visible through binoculars and telescopes.

I thought this would make for an interesting imaging target. But first, how to find it? Well, Bill Rogers over at Cloudynights was kind enough to put a post with Stellarium scripts for locating this comet. One these are stuffed into Stellarium, you can easily find it. Poke the RA/Dec into your scope and you’re off to the races!

Comet 103P-Hartley

Comet 103P-Hartley

Processing comet images turned out to be a lot more challenging than I expected. In particular, all the issues around field rotation and the speed of the comet make for interesting “alignment” challenges. The parallax angle of this short period comet is such that you can actually “see” it move through the sky if you watch long enough. In other words, the comet is moving really fast and is real close by, while the stars in the background are so far away that they almost don’t even look like they are moving. Imagine a car driving 50 mph and driving by one foot away vs the same car driving by at one mile. The cat a mile away will look like it is moving much slower.

The streaks in these images are from stacking individual images on top of each other. The spottiness is due to some of the individual frames not quite turning out good enough for the stacking procedure. While imaging, from frame to frame, you could actually see the comet moving through the sky.

This core of this comet is pretty small, about 2km in diameter, and predictions are that it will be vaporized in less than a thousand years. So you had best get to looking now while you still can :)

Our ancestors believed comets would swoop down and steal your children — this one looks like it is coming fast!

Comet 103P-Hartley

Comet 103P-Hartley

The sub-exposures for these images are the same, but the processing is a little different. Imaging scope was the the Celestron CPC 1100 with f/6.3 focal reducer, and the camera was the Orion StarShoot Pro v2.0. The first image I used a Sigma Clip combine and allowed the rotation to make itself evident (notice the star streaks are arcs). I centered these images on the comet itself for the stack. The second image I used software for derotation, but still centered on the comet. Failing to center on the comet itself would result in the comet streaking while the stars didn’t. Interesting for finding new comets, but not good for imaging a current one. The second image is build with the “sum” method of stacking images.

In the next few weeks, 103P/Hartley will be getting bigger and the moon will be going away which ought to make way for some additional nights where imaging should be possible. Here’s a small snippet of Stellarium with the above script and some of the more interesting locations where this comet will be in the next few weeks. These star maps should make it a bit easier to find comet 103P Hartley!

How to Find Comet 103P Hartley

How to Find Comet 103P Hartley

UPDATE: I’ve updated the chart of where to find Comet 103P Hartley through October

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