Sky Events

(revised 8/25/08)

Planets. Jupiter is the only planet easily visible in the evening hours. Look low in the south: it's the brightest thing you'll see. Watch the gibbous (more than half illuminated) Moon pass below Jupiter on September 9.

International Space Station. The International Space Station (more info here), the largest satellite in orbit and the only one inhabited by human beings, is occasionally visible to the naked eye. It looks like a moving star. Its brightness varies, but it can rival the brightest planets and outshine the brightest stars when conditions are optimum.

We have a couple good morning passes coming up, but no evening passes until mid-September.

Wednesday, August 27, 5:58-6:03 a.m. Rises in the southwest (SW); reaches maximum altitude* very high (76 degrees above the horizon) in ENE; sets NE. Magnitude* -2.1, or brighter than any star and all planets save Venus (which is not visible at the time, anyway).

Friday, August 29, 5:18:23-5:23 a.m. Appears out of Earth's shadow low (altitude 28 degrees) in WSW; peaks very high (80 d. up) in NW; sets NE. Magnitude -2.4, or a bit brighter than Monday's pass.

Sunday, August 31, 4:40-4:42 a.m. Appears halfway up (actually, altitude 50 d, its maximum for this pass) in NNE; sets NE. Mag -1.6, or fainter than the other two listed here (but still far brighter than any star).

There are other, fainter passes visible during this time. For more information about the ISS, and about other satellites' appearances, look at Heavens Above.

* Altitude: angular distance in degrees above horizon, NOT distance in miles above Earth's surface. Straight overhead is 90 degrees, halfway up the sky is 45, the horizon is 0.

  Zenith: the point straight overhead.

  Magnitude: brightness. The brightest star in the winter sky, Sirius, has a magnitude of -1.4 (negative numbers are brighter); the brightest summer star, Vega, is at 0.0. Jupiter stands at -2.5, Venus at -4.0. The faintest star visible to someone with excellent eyesight is around +6. The Sun is -26! Magnitude estimates for the Station and Shuttle are typically underestimates: they usually appear significantly brighter than the numbers would lead you to expect. Also note: an evening pass starts out quite dim (because the Sun is shining mostly on the part of the spacecraft facing away from us). The satellite becomes brighter as it reaches its peak altitude. So have patience: don't give up too soon! Sweep your eyes along the expected path; look for a moving dot that doesn't blink. Morning passes start out a bit brighter, so are easier to pick up right away.

  Weather conditions: as I tell my students, I can't be held responsible for anything that happens less than 100 miles above the Earth's surface.

Star charts, sky maps. One of the most comprehensive star charts available is at SkyMaps.com.

Questions about this page? Contact the planetarium director.

(Back to Announcements)