Friday, August 24, 2012

Stargazing on a Cloudy Night

Over the last year or so I've become interested in backyard astronomy. Growing up in south Florida, I was always fascinated by the rocket launches out of Cape Canaveral.  I remember having one of those cheap "department store" refracting telescopes, but it wasn't worth using for anything more than looking at the moon.

So last year I started reading more about astronomy, and even wound up buying a nice budget-friendly telescope, the Orion SkyScanner 100mm. It's a right nice little scope, and something I enjoy doing is going out on a clear night and taking a look at what's out there. When I head out, I tell my wife I'm going to go listen to "the heavens declare the glory of God." (Psalm 19:1)

The scope comes with a version of "Starry Night," a software planetarium package. It appears to be well regarded, but I run Ubuntu Linux on the machines at home.  For a while I tried to get Starry Night to run under WINE, but to no avail.  So I went hunting for planetarium software which runs under Linux.  I found Stellarium which I think is a fantastic package. It is open-source, and available for Linux, Mac, and Windows. 

One of the neat things about planetarium software is that if it knows where you are, it can tell you what your night sky looks like. So go ahead and download Stellarium, and configure it for your particular location.  Take a look at a constellation or two, and then go outside to see if you can find them for real.

Stellarium includes a number of "plugins" which add to its functionality. I found that with the "Oculars" plugin, I can configure Stellarium to show the sky exactly as it appears through my telescope. I'm going to show you how to do that yourself; it's a fairly straightforward process.  But before you begin, you are going to need to collection a little information:

  • What's the aperture and focal length of your telescope?  Mine is 100mm, focal length 400mm
  • For each eyepiece, what is its focal length and apparent field of view (aFOV)?  I'm going to define two eyepieces, one 10mm eyepiece (aFOV=52) and one 20mm eyepiece (aFOV=52 as well).  You can find aFOV information by looking at the technical specifications for the eyepiece. You can find this at the manufacturer's website, or you can use one of the many online calculators.  For example under the Specs tab here you will see the focal length and apparent field of view for the 10mm eyepiece I have.

Now let's begin
  1. Enable the plugin. In Stellarium, open the Configuration window and select the Plugins tab.  One of the plugins should be titled "Oculars."  Feel free to email a thank you note to its author, Timothy Reaves.  Down at Options, click "Load at startup," then click "Configure"
  2. Add your telescope.  Click the Telescopes tab. You will see a couple of predefined telescopes. Click the Add button. You'll see a new entry called "My Telescope."  Change its name to something you might prefer, and then enter its focal length and diameter.  For my telescope, the focal length is 400, and diameter is 100. My particular telescope is a reflector, so I need to click "Horizontal Flip" and "Vertical Flip" so the image Stellarium presents is like what I'll actually see.
  3. Add your eyepieces. Click the Eyepieces tab. Click the Add button. You'll see a new entry called "My Ocular." Change its name so something you'd prefer, like perhaps "Orion 10mm". Enter the parameters you found for the ocular, ie, the aFOV and focal length.
  4. Test.  Click on any particular target in the sky, then select Ocular View (Ctrl-O [O as in Ocular]).  Once in Ocular View, to select your particular telescope, click Alt-O, scroll to "Select telescope," and select the telescope you want to use. Do the same for the ocular. What you see in now should be pretty much like what you see with this particular telescope/eyepiece combination outside.  Stellarium will also show the view parameters in the upper left of the screen.

I use Stellarium configured for my telescope to help me plan star-hopping to various targets. I can "aim" Stellarium at my starting point, then switch to ocular mode, then along with a star atlas star-hop to my target location. Knowing what my waypoints will look like in Stellarium helps me know what they are going to look like through the telescope outside. And I can stargaze anytime I want, even on a cloudy night.

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