Skip navigation

Tag Archives: astronomy

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.


Have you ever considered updating the firmware of your Celestron NexStar? My hand control was running version NXS 4.13 and my motor control was running version 5.13, so updating my firmware was long overdue. In case you didn’t know: the Celestron NexStar 5SE contains two separate computers that each run their own firmware version. You can find the versions of your telescope’s firmware via the Utilities Version menu:

Why would you update your firmware to begin with? You can be sure that your telescope will run with more precision and less bugs with a newer version of the firmware. And amazingly, my NexStar is now more quiet than it was before! A very good reason to have updated the motor control firmware indeed! Read all about it here if you are curious.

The Celestron firmware update software is available only for the Windows operating system. So I decided to update my telescope’s firmware via Parallels for OSX, since I am using a Macbook Pro with OSX.

First I had to get the correct cable(s), though. To update the telescope’s firmware, you either need an old computer that still has an RS232 serial port, or a USB-to-serial adapter. With my Macbook Pro, I had to opt for the latter.

I bought a Plugable USB to RS-232 DB9 Serial Adapter (Prolific PL2303HX Rev D Chipset) on for $12.95. You also need an rs232 cable that connects to the bottom of your hand control. Read all about it here. I got my rs232-to-handcontroller cable at our local Celestron dealer, Here you can see how that cable connects to the hand control:

I downloaded two installers from the Celestron site. One to update the motor control firmware (MCUpdate), the other to update the hand control firmware (HCUpdate). After installation, I started with the motor control update. MCUpdate allowed me to download the latest version via the web. You can see how this looks further below, where I describe the hand control firmware update, which uses a very similar procedure. I had to connect to COM3 in order to communicate with the telescope, but your COM settings may differ.

After clicking on “Begin programming”, the motor control firmware was updated. It took a few minutes to complete, during which time the hand control was in a locked state.

Updating the Hand Control firmware was very similar. Again, I had to choose COM3. But in order to update the hand control firmware, I had to hold down the INFO and UNDO buttons on the hand control while turning on the power. This resulted in the following message:

Like MCUpdate, HCUpdate also let me download the latest firmware version from the web:

After clicking “Begin programming”, the software again showed me the progress of the firmware update:

For me the whole procedure was completely painless. It took a few minutes to update each firmware version. Be sure to follow all the prompts, both from the Celestron update software and those on the hand control of your NexStar 5SE. For instance, at a certain point during the procedure I had to power cycle the telescope. But when all was finished, the Utilities Version menu happily showed me that the new versions were installed:

Messier 81

That’s M81, first time I found it in this light polluted town. Also the first time I polar aligned my Celestron NexStar 5SE. I highly recommend polar aligning your scope, especially when you’re gonna do astrophotography. Why? Because a polar aligned telescope only rotates on one axis with a single motor (which means: more precision) and the photos don’t rotate from one frame to the other. But because the alignment procedure is quite involved and not well documented in the manual (or on the internet for that matter), here’s what to do if you too live on the Northern hemisphere. PS: This is the absolute minimum. We’ll cover an additional wedge align in another post.

1) The NexStar 5SE has a wedge. This wedge must be lifted such that it’s adjusted for your latitude. In my case, I live at latitude 52º, so I align the base plate to the 52º mark. You can do this during day time:

Wedge latitude align

2) Setup your telescope outside to let it adjust to the temperature and power on the NexStar computer and the GPS. Set it up in this initial position, pointing to Polaris. You can move the tripod around such that Polaris is more or less centered. It is important that you point your telescope to Polaris as good as you can.

Initial position

3) Wait until the GPS is linked:

GPS linked

4) When the GPS is linked, choose EQ North Align:

Polar alignment - EQ North Align

5) The first thing the NexStar asks you to do is “Set Alt to Index”. You need some light (e.g. from a red lantern) for this, and it means that you use the up/down controls of your NexStar hand control to align the two arrows:


When you have done this, the telescope is pointing towards the ground! This is exactly as it should be!

6) The NexStar now asks you to “Find the Meridian”. This is the tricky bit:

Find meridian

You now have to slew the telescope with the hand control’s right arrow button so that it points towards the sky AND is aligned to the meridian. In the sky, the meridian is the imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the horizon, and through the nadir, and is perpendicular to the local horizon. This means you have to swing the telescope clockwise for a half turn (180° or π rad if you like math) until it points to the sky again, away from Polaris. It helps me to put my iPhone with a compass app on top of the telescope until it is aligned North to South:

Polar alignment - iPhone compass to find meridian

Your telescope now points to the sky, away from Polaris!

7) Now choose “EQ Auto Align” and align the telescope as you normally would do to two of the suggested stars:

Polar alignment - EQ AutoAlign

8) Voila! Your NexStar is now polar aligned. For more accuracy, you can still use “Precise GOTO“. In fact, that’s how I found the above Messier 81. My first trial with the regular Messier menu found nothing. But “Precise GOTO” yielded a much better result; M81, dead center!

Of course I would like to improve on this result. I think I can aim a little higher on the following, considering the equipment stays the same:

  • Find a place with less light pollution.
  • Take more pictures.
  • Also do a wedge align and generally make sure M81 stays better centered on the ccd.
  • Spend more time focusing.
  • Experiment with exposure settings. At 10″, M81 seems to “blow out” at the center. So less may be more here.

Stay tuned for another photo of M81.

%d bloggers like this: