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The Purpose | The Application | The Details
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"Satellite Finder Online (PHP)" (hereafter SFO) is a Web-based version of my popular Java application "Satellite Finder". This service provides coordinates to help you locate geostationary satellites, primarily for those installing and pointing satellite dishes. If you are a professional dish installer and you expect to be in the field at the time you need pointing information, you may want to download "Satellite Finder" as well (both services are free).
To use SFO, just select a state and a town, or type in a ZIP code, and this program will generate a list of coordinates for most geostationary satellites. You may also type in any geographical position if the ZIP code database doesn't cover your location.
There is more complete documentation below the application.
SFO solves a problem becoming more important as we become more reliant on satellite communications. Basically, there is now a ring of very expensive jewels circling the earth in a special orbit. Science-fiction writer Arthur C. Clarke first had the idea that a particular altitude would cause a satellite to appear motionless to the revolving earth below. That orbital height, about 22,300 miles, perfectly balances a satellite's orbital velocity with the earth's rotational velocity. This means we can install satellite dishes that point to particular locations in the sky, and the satellites won't drift out of view.
Because all the satellites lie directly over the equator, and because they are all at the same altitude, the mathematics required to produce viewing angles is relatively simple. In fact, the challenges in the design of this page (and of the similar Java application Satellite Finder) lay more in the area of managing a huge database of ZIP codes and associated positions that is presently over 40,000 records in size.
SFO will remember a ZIP code you enter, and when you return to this page (assuming you have cookies enabled), it will recompute your last ZIP code entry. But if you want to tell SFO which ZIP code to compute without actually entering it, just produce an URL (Uniform Resource Locator, a fancy term for a Web address) that looks like this:
http://www.arachnoid.com/satfinderonline/index.php?zipcode=98339
Some users will need to enter position coordinates directly, without using the ZIP code database. One can type in coordinates by hand, but again, if you want to compute a particular position without having to manually enter the values, create an URL like this:
http://www.arachnoid.com/satfinderonline/index.php?lat=42&lng=-120
Using this system, one could create a personal list of URLs containing frequently-used ZIP codes or positions, and click the one needed for a specific purpose without having to hand-enter the values.
Remember these rules:
The SFO database doesn't contain all ZIP codes, only (more or less) those for cities with more than 15,000 people. To compute viewing angles for a location without a listed ZIP code, either:
If you elect to enter a geographical position, remember the entries can be expressed in decimal degrees, or degrees and decimal minutes, as shown in these example entries for 40° 12.5' north:
Remember if you choose to make a single decimal degree entry as in the second example above, be sure the minute value is set to zero.
Turning now to the data table, the columns are:
"Az(t)": The true-North azimuthal angle for the satellite at the chosen site. The Azimuth represents a horizontal circle measured in degrees:
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