Satellite Observing

Sometimes it is a challenge to find something to do after the scope is set up at a remote location and before the sky turns inky black. One thing that an observer can do while waiting for regular observing is to look for low earth orbit satellites. The activity can be done alone or with groups. Diane and I find it especially nice to work together. We share the tasks: reading a list of times and azimuths for satellites that will come over, and recording times when the satellite passes celestial landmarks. We also compete with each other to be the first to see a satellite.

There are several tools available for finding satellites. All of the tools I use involve computers and internet resources.

One easy source for finding out what bright satellites can be seen is Heavens-Above (http://www.heavens-above.com). You tell the site where you are and it will tell you what bright satellites will be visible in the coming evening and morning. Heavens-Above lists both the satellites that are on the publicly available lists and other satellites which are not published. Most of these are the so called “spy satellites” put up by our country and others. They are often big bright satellites, the size of the Hubble Space Telescope, but aimed at earth instead of at the stars.

I have an Ipod Touch. One day I will have an Iphone if I am good and have enough patience. These devices have a couple “apps” that are handy for satellite observing. I downloaded the free ISSLite program from VosWorx. It downloads orbital information from the web and helps folks that want to watch the International Space Station and any Progress spacecraft or Space Shuttle passes. The program lists the passes that will be visible for a location for the next week and it gives two views of the orbital movement of the spacecraft. One view is the traditional view seen at Houston mission control – the sinusoidal wave of the space craft position. The other view is a 3-D rendering of the earth (and the earth can be spun around) which makes for a pretty good tool to explain the traditional view.

Having up-to-date information on satellites is important. Their orbits change over time, and sometimes the change is rapid. Orbits are defined by a series of numbers – there are several that are important to plug into equations to allow calculation of the satellite’s position in space and the viewing angle from an observer’s location. Fortunately, the computer programs that I am writing about here know how to import the numbers – officially called orbital elements or Keplarian orbital elements – and work the advanced math necessary to calculate where a satellite may be visible. As an observer, I need to tell a program where I am on the surface of the earth, and I need to download a current version of the “keps” which are also sometimes called the NORAD Database or the “els”.

There is an advanced version of the ISSLite program that will follow a much larger group of satellites – amateur radio sats, and bright visual sats among the group. That program is also distributed by VosWorx and is called ProSat. It cost about $10 to download. It is worth every penny IMHO.

There are also programs available for laptop computers. One that I have been using recently is Earth Orbiting Objects or EOO. This program, written by Steve Boucher, allows download of recent keps, allows one to store multiple observing locations and does everything that the ProSat program does. It goes one step further. It allows me to see a view of the sky with the simulated satellite going past the starry background. That is, it contains a planetarium program which shows the movement of a satellite across the sky. It can be set up so that it will show in near-real time where a satellite is. That is really good for both finding a dim satellite and for replaying a satellite passage to remember the pass with greater accuracy.

One activity involving satellites and telescope has been a real challenge for me. It is an activity for the nimble observer. On a space station passage, try following the station with a telescope at about 120-150X magnification. For me, it took using a Telrad, a finder scope, and quick reflexes. I was rewarded with a series of views of the station with enough resolution that I could see a distinct rectangular shape and a different color for the station’s wings than for its central occupied core.

A second activity can be done either at dusk/dawn or sometimes in bright sunlight. That is the observation of Iridium flares. The Iridium satellites (used by the global telephone system of the same name) have very bright mirror like sides and they can “flash” an observer with surprisingly bright flares of light. At a maximum they may reach -8 magnitude – much brighter than Venus. The best source of information about Iridium flares for me has been the Heavens-Above site mentioned at the top of this piece.

So, next time you see me with my scope all set up and the sky not yet dark, if no one has engaged me in an interesting conversation and you wonder what I might be doing with all those pieces of paper, my iPod, and a voice recorder… well now you know the rest of the story.