Observing Earth Satellites
The Earth is surrounded by over 9,000 artificial satellites all launched into orbit in the past 40 years. Perhaps you have seen one of these objects as a point of light sailing gracefully across the night sky.
Satellites are best seen about an hour after sunset or before sunrise. Around these times, a passing satellite will reflect sunlight back to a ground-based observer in a relatively dark sky. Low Earth orbiting satellites are not visible throughout the night because at late hours the Earth's shadow will prevent sunlight from illuminating the satellite.
Satellites often appear as a steady point of light and require a few minutes to travel across the sky. They will disappear from view when in the Earth's shadow. Some satellites flash every few seconds, a feature typical of a tumbling satellite such as a discarded rocket body. Certain satellites will brighten suddenly, briefly outshine the brightest stars and planets, and then completely fade from view. Iridium satellites exhibit this behavior because sunlight reflects strongly off their large, highly reflective external panels.
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The brightness of a satellite depends upon several factors including its size and distance from an observer. Very large satellites such as the Space Shuttle, Mir, and the massive International Space Station (presently under construction in space) are quite bright and easily visible to the unaided eye provided you know where and when to look.
An excellent satellite prediction service is available on-line at Heavens-Above.com. Anyone can use this free service to predict visible passages of the Space Shuttle (when in orbit), Mir, the International Space Station, and the dazzling Iridium flares. Go there now and get a few satellite predictions for your own backyard. It's easy!
Elsewhere in the Sky...
A partial eclipse of the Sun will occur on December 25 over most of North America. Consult your local media for times and further details. WARNING: NEVER LOOK AT THE SUN -- IT WILL INSTANTLY DAMAGE YOUR EYES. Instead, use a small mirror to project the eclipsed Sun's image onto a wall.
The bright planets Jupiter and Saturn are well-placed high in the east and brilliant Venus is climbing higher in the southwest. On December 29 Venus will form a close pair with the crescent Moon. Clear skies till next month!