Have you ever seen an Earth satellite? On clear, dark nights, we can see dozens of satellites with our eyes alone. Most satellites travel within a zone called Low Earth Orbit that ranges in altitude from 150 to 1200 miles. To reach Low Earth Orbit, a rocket carrying a satellite must reach a velocity of about 17,000 miles per hour parallel to Earth’s Surface. At that velocity, satellites orbit Earth about once every 90 minutes. Reaching Low Earth Orbit requires powerful rockets that can lift and accelerate satellites. The Cost for launching satellites is decreasing rapidly, as engineers develop reusable rockets. So, the number of orbiting satellites is increasing dramatically.
Satellites are only visible from the sunlight they reflect. Because satellites orbit higher than 150 miles above Earth, they can remain in sunlight, even when areas below them are dark. So, satellites can be visible in a dark sky. The best times to spot satellites are just after evening twilight and just before morning twilight. Satellite passes may last from less than a minute to as long as 7 minutes, when satellites pass high in the sky. Satellites typically shine with a steady light. But if a satellite or rocket body is tumbling, its brightness can vary. And if sunlight strikes a highly reflective surface on a satellite at just the right angle, you may see the satellite “flare”, as its brightness rapidly increases, then decreases. If a moving sky object has flashing red and/or green lights, it’s probably an aircraft, not a satellite.
The brightest satellite is the 300 ft-long International Space Station or ISS, which may appear brighter than the planet Jupiter. Tiangong, the Chinese Space Station, is another very bright satellite. Recently, SpaceX has been launching groups of more than 20 Starlink internet satellites every few days. Trains of Starlink satellites are striking sights from 1 to 4 days after their launch. You can get nightly predictions for visible satellites, including the ISS, Tiangong, and Starlink satellites for any location on Earth from various websites, including NASA’s Spot the Station, Starlink Satellite Tracker, and my favorite, Heavens-Above.com, a comprehensive site for all satellites. And you can find local satellite predictions in “Observing Highlights” from the Black Canyon Astronomical Society.
So, find some predictions and go out and spot the ISS, Tiangong, or other satellites!
You’ve been listening to “Western Slope Skies”, produced by the Black Canyon Astronomical Society and KVNF Community Radio. I’m Art Trevena.
References
https://www.britannica.com/technology/Earth-satellite
https://www.nasa.gov/humans-in-space/leo-economy-frequently-asked-questions/
https://en.wikipedia.org/wiki/Low_Earth_orbit
https://www.nasa.gov/international-space-station/
https://www.space.com/tiangong-space-station
https://en.wikipedia.org/wiki/Starlink
https://spotthestation.nasa.gov/
https://www.blackcanyonastronomy.com/
