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NASA's J-Pass can track satellites from almost any backyard.

May 6, 1999 : If you've ever wished upon a falling star, you may have actually pinned your hopes on a piece of machinery. There are over eight thousand manmade satellites orbiting our Earth every day. Because satellites reflect sunlight back down to Earth as they pass overhead, they often look like slow-moving stars.

Above: The lighter blue area is where the Space Station can be seen from the ground.

A typical satellite in low Earth orbit (LEO) circles the Earth sixteen times each day, traveling 7.5 kilometers per second (27,000 km/hour). The best time to catch a glimpse of a satellite is either at dusk or at dawn, because satellites are most visible when they are in sunlight while the viewer is in darkness.

Left: Patrick Meyer, author of JPASS, and its sister program JTRACK, describes the program and how to use it. Click on the image to view a RealVideo movie. (Go to RealNetworks for a free player, if you need it.)

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The brightest satellites also happen to be some of the most famous: the new International Space Station, Russia's Mir Space Station and the Space Shuttle, when in flight. These larger satellites have been observed to be brighter than -1.0 visual magnitude. That is nearly as bright as Sirius (Alpha Canis Major), the brightest star in the sky.

The trick to identifying these satellites is knowing exactly when and where to look. Using NASA's Liftoff to Space Exploration web site, you can find out which satellites will be passing over your hometown.

All the lonely objects, where do they all come from?

Liftoff's Java program, called J-Pass (at right), uses information provided by the North American Strategic Defense Command (NORAD) for more than a hundred bright satellites. NORAD keeps track of the more than eight thousand objects traveling above the Earth. Over 2,500 of these objects are man-made satellites, both operative and inoperative. Other satellites orbiting the Earth are actually debris: nosecone shrouds, lenses, hatch covers, rocket bodies, boosters, payloads that have disintegrated or exploded, and even objects that have escaped during manned spacecraft missions.


Left: J-Track 3D shows 500 satellites orbiting the Earth.

Accessing J-Pass only requires a recent version of either Netscape Navigator or Microsoft's Internet Explorer. J-Pass gives satellite rise and set times for your location, and indicates the part of the satellite pass that will be visible. The chart even includes positions of visible planets and bright stars. Sky charts can be printed out to be used as an outdoor reference guide. For viewers without a Java ready browser, the Liftoff site also has a mailing list system. By subscribing to the list, viewers will be notified by e-mail of upcoming satellite passes.

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Left: The animation at left shows a simulated pass of International Space Station through the constellation Orion. This is what a bright satellite pass is like. Visible satellite passes occur after sunset and before dawn. JPASS will also tell you the expected brightness of the satellite as it passes overhead (negative numbers are brighter!).

Web Links

J-Pass 2.0 -- from Liftoff to Space Exploration

J-Pass E-Mail Generator -- from Liftoff to Space Exploration

Satellite Situation Report -- from Liftoff to Space Exploration

NORAD - Source of satellite tracking data

Orbital Information Group - NASA Goddard Space Flight Center

German Space Operations Centre -- Satellite viewing site


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Author: Patrick Meyer
Curator: Bryan Walls
NASA Official: John M. Horack

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