21P Falls Through Auriga…

 

21P photographed from Shap, Cumbria, late on the evening of September 4th – Stuart Atkinson

 

Comet 21P Giacobini-Zinner is now just a couple of days away from its closest approach to Earth, but it is getting more and more difficult to see in the northern sky. Having dropped down past Perseus and slid past Capella, the comet – which is too faint to be seen with the naked eye but is visible through a small telescope or a pair of binoculars if you’re looking for it from somewhere with a dark sky – is now falling through Auriga, passing several of that constellation’s star clusters along the way.

Here’s a finder chart (credit: Robin Scagell) showing where you can find 21P over the next few nights…

 

Area of comet 21P/Giacobini-Zinner, during early September 2018, seen looking north east at midnight.

 

But what does the comet actually look like? Images like this one, which I took on Tuesday evening…

 

 

…make the comet look very impressive, with a bright, glowing head and a long, misty tail, but that’s quite misleading. In reality this comet (like most of the comets that appear in the sky) is teeny tiny and faint too. So why does it look so dramatic on that image? Because that is a combination (or “stack”) of ten images, all of the same exposure, taken through a powerful zoom lens attached to a camera that was tracking the stars. Using special – but free – software I combined those ten different images to create a single, more detailed image. Astronomers who photograph the night sky, known as “astro-photographers”, use this technique a lot, and it’s very useful for comet images because comets are so small and faint.

To show just how small this comet is in the sky here’s a wider angle view, showing most of the constellation of Auriga, and the comet circled. You’ll see it is little more than a blurry star…

 

 

See? It’s tiny! I also took a set of images of the comet and a couple of well-known deep sky objects to highlight how small and faint Comet 21P actually is…

 

 

The good news is that we might – MIGHT – have a much brighter comet to see at the end of the year, IF Comet Wirtanen performs as we hope it will. More details on that nearer the time.

In the meantime, take a look at 21P before it drops out of sight. Just find Capella in your binoculars or small telescope and look beneath it for a small, smudgy, out-of-focus “star” with a slight green hue. If you see something like that you’ve found the comet. Good luck!

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