|
Satellites | ||
I started watching satellites in the late 70's when catching them was mostly a matter of luck. I never did much more than pick up Desmond King-Helle's book Observing Earth Satellites and watch a few fly over. In the early 90's, I ran across a program called SatTrack which had a free download for Unix workstations. (version 3.1 is still free for personal use.) Imagine my surprise to see that my Sun workstation could compute the position of over 100 satellites in real time and display their coordinates as they flew overhead.
With the power available in today's personal computers, you can perform calculations that were, until recently, possible using only the largest computers reserved exclusively for the military and academia. There are programs available today for almost every computing platform from the Mac to Linux.
Right now, I'm using SatSpy on the PC to do most of my tracking. With a laptop, you can have a real-time display of the sky right in front of you as you sit beneath the stars. With a recent set of satellite data, spacecraft will often appear within a second of the predicted time. Don't forget to set your watch by an atomic clock so you have the real time. When its freezing cold outside, its quite a feeling of power to step outside 20 seconds before the satellite is going over, watch it, then duck back in. Great party trick - impress your friends! (if they're geeks)
For the casual observer, after seeing the first few satellites, the thrill is pretty much over. However there are a few phenomena that are really worth watching. These are Iridium Flares, and Space Shuttle re-entries. The web resources below will help you find when these special events are visible in your area.
Aside from the tracking software above, you'll need two other things to get started - your latitude and longitude to a high degree of accuracy, and an accurate time source. Fortunately, you can get both of these from the web. Watching for satellites is a lot more fun if your time source is accurate to a second or so.
Many of the modern computerized telescopes have the ability to track satellites as well as astronomical bodies.
My favorite tracking software, SatSpy is no longer in production, so I've been looking for something to replace it. The latest experiment is to see if I can compile SatTrack for Mac OS X. (this is version 3.1.1 - you might try here for version 3.1.6 or 3.1.7). So far, it seems to work with some minor changes to the distribution. The compiler flags are:
# Mac OS X CPU = G4/OSX CC_CMACH = -O -DFREEBSD -DIOCTL CC_LMACH = CC = ccand the linker options if you're using (XDarwin's default locations) are
LX11 = -L/usr/X11/lib -lX11 -lXt -lICE =lSMand there is one Y2K bug in the program that can be fixed by adding the line
if (*year > 99) *year = *year - 100;to the function getUnixTime in sattime.c right before the return. The program works because it assumes elsewhere that dates >50 are in the 1900's and dates < 50 are in the 2000's - the original programmer just missed the implications in this one spot.
#define MAXSATNAMELEN 24 /* max. length of sat name */
Last modified on