Spotting the Space Station
 Q:
It seems that the space station, with its newly installed solar arrays should be visible to the naked eye.
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Is it visible to the naked eye?
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How bright, in comparison to the brightest planets Venus, Mars and Jupiter, is the space station?
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What is the celestial path of the space station and how can we calculate the next possible observation of it?
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When will the next sighting be possible from the northern hemisphere?
A:
Yes, it is visible to the naked eye and best seen near dawn or dusk when the Sun lights the International Space
Station and you are in near darkness.
The Station is brighter sometimes than others, depending on its illumination and distance from us. It has a maximum
brightness of -2.8 when it's fully lit and nearest (about 367 kilometers) to Earth. That's a little brighter than Jupiter (-2.5). When the Station is only halfway lit and 1,000 kilometers distant, it's brightness is only +1.5--about as bright as a
dim Mars.
Mars varies in brightness from -3.0 (outshining Jupiter) to +1.6. Venus has a magnitude of -4.4, which is the brightest object in the night sky, except for the full
moon (-12.7). We measure star brightness with a logarithm scale, similar to the way we measure earthquake magnitudes.
The Station's celestial path is an oval-shaped path--an elliptical orbit, which varies from 228 to 235 miles from Earth. Going 17,500 miles per hour, the Station
circles Earth 16 times a day at an average altitude of 372 kilometers (231 miles) and an inclination of 51.6 degrees to the equator. The Station eventually crosses
almost every point on Earth: flying over 85 percent of the globe and 95 percent of its population.
You can get tracking software to calculate the next sighting (see Further Surfing) but it's easier to surf the web to any of several tracking sites. I like the
Heavens Above (http://www.heavens-above.com/) and Sat Passes (http://www.bester.com/satpasses.html) sites because they not only give you the next sightings
but they also grade the sightings, telling which is brightest.
You just enter the name of your city (or its latitude and longitude) and... presto! The program displays screens giving several days of sighting times, how to
locate the Station each time it passes, and how visible the Station is during the pass.
For example, I live in Albuquerque, New Mexico. I just had a good sighting on the 12th of December at 18:06 MST. I looked to the west/southwest (244
compass degrees) to see the Station rise above the horizon at 18:06. I followed the rising satellite to the northwest where it reached its maximum elevation (36
degrees, or about 2.5 handbreadths, at arm's reach) for this pass at 18:11, and then watched it set at in the north/northeast at 18:16. The program provided all
this information so I could tell where and when to look.
The next good one in Albuquerque will be on the 29th of December about 17:52, rising in the northwest. I can hardly wait.
Further Surfing:
The Discovery Channel's interactive website. Explore the inside of the Space Station; learn basic mission facts.
Heavens Above, tracking site
Sat Passes, tracking site
NASA orbit trajectories and tracking software, http://spaceflight.nasa.gov/realdata/elements/index.html
(Answered by April Holladay, science correspondent, December 13, 2000)
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