Automated Astronomy

As you may know from this blog, I’m a huge fan of Stellarium. For me, it is the go-to program for what’s in the skies, when, and where. While it’s true it won’t necessarily have the latest and greatest ephemeris for stuff like new comets that rapidly change their courses or indicate they’re not going to live up to the hype (or are exceeding it), that data is added easily enough. You can either add it automatically with a few clicks inside the program or add it manually to a configuration file. Plus you can easily set up multiple locations for your various viewing sites. ‘Nuff said…Stellarium rocks!

I’ve known for quite some time that in the Configuration / Plugins section there was this little item called “Telescope Control”. Until I got my latest telescope, the Celestron NexStar 102 GT, I didn’t have any telescope with GoTo capability or that could be controlled through a computer program. Now that I do, that little plug-in became far more interesting to me.

picture of the Celestron 102GT telescope in my living room.

Celestron 102GT telescope

Naturally, I went surfing to find out what was needed and if it would even work with my telescope. It was a little confusing…some posts said you needed to install this or that before it would work, others said you didn’t, and of course there were the usual “this is better” posts. Careful reading and attention to the dates of the various posts plus checking what was in the plug-in configuration popup indicated that NexStar telescopes were supposed to be supported. So far, so good.

In the course of my research, I came across this site: NexStar Resource Site. There is a wealth of NexStar information there, along with what I most wanted to find…instructions for making your own computer to telescope cable.  There, ready for my consumption, were the instructions for the serial port to hand controller cable I needed for the 102 GT. Excellentamente!!!

Looking over the pin-out diagrams, it seemed easy enough: get a telephone handset cord, a female DB-9, a housing for the DB-9, solder three pins, and done. Ironically, soldering the wires was easier than manhandling that coiled cable into the DB-9 housing. I probably had the soldering done in less than 10 minutes but it took me almost 20 minutes and some electrical tape to clamp the coiled cable and get it to stay in one half of the housing while I assembled the other half onto it. In the end, though, I had my cable. Since I didn’t want to blow my telescope, I triple checked the pinout before soldering each one, used my meter to verify pinout to pinout, and triple checked the pinouts when I was done. Yeah, I’ve been known to get a wire or two wrong once in a long time, so I was definitely not going to make a mistake here.

Picture of ivory coiled phone handset cord with female DB-9 in grey housing attached to blue TrendNet TU-S9 Serial to USB converter.

Homebrew cable for Celestron 102GT with TrendNet TU-S9 Serial to USB converter.

The cable is for use with a serial port but my laptop doesn’t have a serial port. So I used a TrendNet TU-S9 Serial to USB converter. It’s worked well for my ham radio TNC so I saw no reason it shouldn’t work here. Plugging that into the laptop, I went into the computer’s Device Manager and looked up the port it was on. This is necessary because Stellarium needs to know what serial port the telescope is connected to. Every time you use the serial to USB converter with Stellarium, it’s a good idea to always use the same physical USB port. That way you don’t have to constantly change the COM port assignment inside Stellarium. Trust me, it’s not that hard to change, but it’s nicer just firing up Stellarium and turning on the telescope control. Checking Device Manager showed my converter on COM6.

Then it was time to fire up Stellarium. I’m running version 0.12.0, which meant I had the latest version. Hopefully, the telescope plug-in would be painless. In the end it was surprisingly easy, far more easy than I expected based on everything I’d read. The process was superbly simple:

  1. Start Stellarium
  2. Go to Configuration / Plugins
  3. Select “Telescope Control”
  4. Select “Load at startup”
  5. Close all popup windows
  6. Exit Stellarium  (have to restart so the telescope control plugin loads)
  7. Start Stellarium
  8. Go to Conrfiguration / Plugins
  9. Select “Telescope Control”
  10. Select “configure”
  11. Enter name for telescope, in this case ‘Celestron 102GT’  (original, eh?)
  12. Enter Com port, in this case ‘com6’
  13. Select the correct device model, in this case ‘Celestron NexStar (compatible)

That’s it. That’s the complete setup and you only have to do it once.  Now to hook up the telescope to the laptop….

In order to use the telescope with Stellarium, the telescope first has to be oriented and aligned. If you think about it, it’s kind of obvious why. Stellarium on the laptop shows you a view according to where you tell it to “look.” You can easily be facing south physically and have a view on the screen of the sky to the west. In order to properly show the telescope’s orientation on the screen, it assumes the telescope has already been aligned with the sky and reads it’s orientation from the onboard computer.

Picture of Celestron 102GT telescope hand controller with homebrew computer cable attached.

The 102GT hand controller showing the homebrew computer cable attached.

So, I did a two star alignment using the telescope’s hand controller. Actually, I faked it since I was in the house and just wanted to verify the cable would work. So, “alignment” done, I connected the telescope hand controller to the laptop with my new cable, then went into Stellarium and performed the following:

  1. Go to Configuration / Plugins
  2. Select “Telescope Control”
  3. Select “Telescopes”
  4. Click on the “Celestron 102GT” listing to highlight it. It’s the only one I have at this point, anyway.
  5. Click on the “start” button at the bottom of the listing area.
  6. Verify the status in the first column has changed from “stopped” to “connected”.
  7. Close all popup windows.

From what I’d read, at this point I was supposed to see a red crosshairs type reticule with the label “Celestron 102GT” beside it, but I wasn’t seeing it! What the heck could have gone wrong? Did I need to add supporting software after all? Then I remembered…the telescope was aligned, but where the heck was it pointing and what part of the sky was Stellarium showing? The last alignment star had been Sirius, so I did a search in Stellarium for Sirius. The image slewed around to the east (I’d had Stellarium looking to the southwest) and there it was, the red reticule circle labeled “Celestron 102GT” centered on Sirius!


I was so excited. I promptly looked for Betelgeuse and immediately clicked on it to have Stellarium lock on it. Once Stellarium’s crosshairs centered on it, I hit CTRL-1. Wahoooo! The telescope promptly slewed over and up and the red telescope reticule moved across the image on the laptop to lock onto Betelgeuse. Checking to make sure the telescope was clear and all cables free of encumberances, I searched for something further away…M31, the Andromeda Galaxy. Stellarium showed it was nicely up in the sky and with nothing in the way of the telescope, I hit CTRL-1. Gleefully I watched the telescope slew around as the telescope icon moved across the sky on the laptop screen. It locked right on M31 and the telescope stopped, patiently tracking the Andromeda Galaxy and waiting for me to view it. If only the walls weren’t in the way and it was dark out!


I was so excited that it worked flawlessly without having to tweak anything or add any supporting software that I had to go get my wife and show her how I could control the telescope with Stellarium. Like a little kid, I happily moved the telescope from object to object a couple times and we enjoyed the moment. Probably me excitedly and her bemusedly.

I am so looking forward to using this setup in the field. I have three projects in mind, right now, for this system.

Number one, I want to build a much sturdier tripod to mount the telescope on. The one I have works, and it’s steady enough after it settles down, but the 35 inch OTA (Optical Tube Assembly) is just too susceptible to external influences and so easily vibrates. I’ve seen quite a few nice looking wooden tripods on the internet that I will use as guidance building mine.

Number two, I need to build a case for transporting the telescope safely on the dirt roads I travel to my favorite astrophotography sites. This, unfortunately, has to wait until after I build the tripod so I can figure out if I want to include the tripod in the case or just the telescope tube. The more I look at tripods the more I think it’ll just contain the OTA and the drive base. The tripod proper will go into a carrying case, most likely.

Number three, I need to build either a piggyback mount or a direct mount for my camera so I can use the telescope or the base to track deep sky objects such as the Orion Nebula, Thor’s Helmet, the Beehive Cluster, M31, etc. for the long exposures necessary. I’d like to try and photograph as many of the Messier objects as I can and many of these will need to be tracked to get a good astrophotograph. I think I might build both for the flexibility of using the camera either with or without the OTA. Both mounts are already designed in my mind and it’s just a matter of getting the materials and building them.

Now if I could just get some clear skies….


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One Response to “Automated Astronomy”

  1. Andrew Says:

    Lol…..I like it when a plan comes together!. Good job!


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