SCAS – Southern Colorado Skies / June 12 – 18, 2016

Consider a planetarium program to help you plan your observations. There are many commercial products available, and a very good program (Cartes du Ciel) is available free at

Interesting Facts about Satellites


  • Satellites don’t propel themselves through the sky. They are perpetually falling – it’s just that they are traveling fast enough that the arc they follow matches the curvature of the Earth below. (For the same reason, astronauts are not weightless because there is no gravity – they are always in freefall!).
  • Because gravity weakens with increasing altitude, the closer a satellite is to Earth the faster it has to travel to maintain a stable orbit. If a satellite needed to change its flight plan to a lower stable orbit, it would have to speed up!
  • If you see a satellite crossing the night sky in a couple minutes (about the same speed as a high-flying commercial jet), it’s probably a typical military or communications satellite which travels in an orbit from about 250 to 600 miles up. If it’s traveling much faster than that, it’s probably an old or defunct satellite just above the atmosphere about 110 to 130 miles up, and will soon burn up as it continues its descent.
  • Satellites always travel from west to east. (If it’s edu_jason-2_satellitescrossing the sky from east to west, maybe you need an eye examination or maybe you’ve really seen a UFO!). The reason for this is that satellites are launched toward the east, the same direction that the Earth spins, to get an assist (like throwing a fastball from a moving pickup truck) that saves fuel. Also, the Earth spins fastest at the equator, so countries launch from as near the equator as possible (NASA did not select Cape Canaveral because it’s close to Disney World!) The exception is some military satellites in north-south polar orbit, which allows them to scan the entire Earth in a single day.



Wednesday (June 15)

Jupiter’s moon Io reappears from eclipse out of the gas giant’s shadow about 8:46 p.m. MDT, a little east of the planet.

Thursday (June 16)

Look for big and bright Mars below the gibbous Moon tonight.


Mercury (in Taurus)

Look for Mercury in the dawn sky with binoculars (beware of the Sun!) just above the east-northeast horizon about 20 or 30 minutes before sunrise.

Venus (in Taurus)

Lost in the glow of the Sun.

Mars (in Libra)

Mars was closest to Earth on May 30th but it’s still big and bright. Look in the southeast as night falls, then south later at night.

Saturn and Antares lie to the east (lower left) of Mars at dusk.

Mars will shrink a little as the week progresses, from 18.3 to 17.7 arc-seconds in diameter. Mars is now a great view even in small telescopes – but get your viewing in now or wait another two years for the next opportunity like this one!

Jupiter (in Leo)

Look to the southwest during twilight.

Saturn (in Ophiuchus)

Look well east of Mars. The red giant star Antares is to Saturn’s lower right (west).

Uranus (in Pisces)

Low in the east just before the onset of dawn.

Neptune (in Aquarius)

Well up in the southeast sky at daybreak.


Sorry – these are too numerous to list here! If you’re serious, load the ISS DETECTOR app on your smart phone or tablet. Alternatively, refer to SCAS member Chuck Percival’s column in the Sunday Pueblo Chieftain.

Have fun!

Dave Furry, SCAS Director of Education


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