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Okay so you hear about a comet that’s supposed to be visible right now. It’s not very bright, but you’ve heard it should just be visible in your telescope. How do you go about finding such a celestial object? In this example we’ll use Stellarium and my Celestron NexStar 5SE telescope. The latter has a 5 inch diameter, so that pretty much limits my possibilities to the brighter comets. Especially since I live in a light polluted area, I can only dream about seeing objects less bright than magnitude 8. In fact, that’s already stretching it pretty much. Magnitude 7 is a more realistic limit (yes, the lower the magnitude, the brighter the object!).

First we fire up Stellarium, a great free open source planetarium program that runs on all major operating systems. It’s feature packed and very precise. Exactly what we need for something like a comet, which, as you may or may not know, moves through the night sky pretty fast compared to the background stars. It’s of course much much slower than a meteor, but if you take several pictures in a row, you can easily see the comet move from frame to frame. It all depends on the orbital parameters (ephemeris) of the comet, of course. Here you can see how I took a few photos of comet C/2009 P1 Garrad where the comet moves relative to the background stars in mere minutes.


Right now, comet C/2012 K1 PANSTARRS is positioned pretty good for where I live. According to Stellarium, it “shines” at magnitude 7.89. It’ll get brighter throughout the year, but maybe the ccd of my camera can gather enough photons to make this thing visible. If you’ve just installed Stellarium, make sure it has the correct location on Earth. F6 will give you the Location window:


To find current comets (and minor planets and all), go to the Configuration Window (F2) – Plugins – Solar System Editor:




Here you can specify that the Solar System Editor should [v] Load at startup. Click on the configure button next to that to configure the Solar System Editor. Navigate to the Solar System tab:


Yours may be empty at this point, because my configuration of Stellarium already loads a bunch of comets and minor planets. Click on the button that says Import orbital elements in MPC format…



At the Lists tab (see above) select Comets where it lets you choose between Asteroids and Comets. Then where it says Select the source, you choose Download a list of objects from the internet. At the dropdown control (Select a source from the list) you choose MPC’s list of observable comets. If this not an option, you can manually specify the following location in the text control that says Or enter a URL:

Now click on Get orbital elements. A new import data window should appear with a list of found objects:


Check the comet you want to find and click on Add objects. In the search window of Stellarium you can now type the name of this comet to see where it’s located in the night sky at a certain time and place. F3 will give you the search window:


The Stellarium search window is a bit of an odd duck. It suggests things you are looking for, but it doesn’t autocomplete like other software. You have to keep typing until you see what you were searching for. If there’s a list, the up and down arrows on your keyboard will let you move through the list and hit Enter when your object is bold faced. When there’s only one option left, you can simply hit Enter.

Armed with the Date and Time window (F5) you can now find a good time for observing the comet:


You can also change the date to find a better moment to watch a comet. Here for instance you can see that October this year the comet might be better visible at magnitude 5.91:


Do remember that comets are unpredictable and this figure might be off. It’s just a guess of how the comet will behave. To use the Precise GOTO feature of my Celestron NexStar 5SE telescope, I need the exact RA (right ascension) and DEC (declination) of the comet at an exact time. For this we will use the figure from Stellarium called RA/DE (of date) from the Search window:


When it’s exactly that date and time, make sure your telescope is pointed at that exact RA + DEC via the Precise GOTO menu of the NexStar computer. As this process takes at least a minute or two to complete, better start a few minutes earlier. If the apparent motion of the comet against the background stars is very high, the comet should move into your eyepiece when that exact moment arrives.

As you can see, comet C/2012 K1 PANSTARRS is well above the horizon tonight at the perfect location of Leo Minor, below the Big Dipper or Ursa Major.

Here’s an example photo of another comet (C/2011 L4 PANSTARRS) which I found exactly with the above described procedure.


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