Last modified: Tuesday, August 5, 2003
Mars and the Perseids light up the sky
Mars will completely dominate the night sky during August as it comes closer to Earth than it ever has in recorded history. Its only competition will be the annual Perseid meteor shower, a fond summer memory for many people.
This year the Perseid meteors must also compete with the moon, however. At the shower's peak on the night of Aug. 12-13, the moon will be just one day past full. The brighter meteor streaks will still be visible, but the fainter meteors will be swamped by the bright moonlight, especially amid the lights and haze of a city sky.
The best meteor-watching time will be between midnight and the start of morning twilight, when the part of Earth where you are watching the sky is facing into the oncoming stream of meteors. The best strategy may be to get up very early on Aug. 13 instead of staying up late the night before. The number of meteors will rise during the pre-dawn hours, and the chance of seeing fireballs will increase as well. There will be some meteor activity for a few hours on either side of the peak time, as well as during the nights immediately before and after the peak.
The Perseid shower's peak rate is typically about 60 meteors per hour under ideal conditions, when the sky is clear and there are no bright sources of light nearby. Try to get away from as many artificial lights as possible to minimize the effect of light pollution, which can obscure as many as half of the visible meteors. A reclining lawn chair will make it easier to watch the sky.
The meteors may appear anywhere in the sky, but they will seem to originate from a point in the constellation Perseus, from which the Perseids get their name. The higher this apparent point of origin is above the northeastern horizon, the more meteors will be visible. Perseus is just north of the W-shaped constellation Cassiopeia in the Milky Way.
Most meteor showers happen when Earth crosses the orbit of a comet. The meteors are caused by tiny particles of dust that were released from the comet's nucleus and left behind in space as the comet got closer to the sun. The Perseids come from Comet Swift-Tuttle. As Earth plows through this stream of particles, each one hits our upper atmosphere at a speed of more than 50 kilometers per second and burns up almost instantly from friction with air molecules. The resulting heat momentarily creates a streak of glowing air that we see as a meteor (sometimes called a "shooting star" or "falling star").
Meteor watchers who would like to contribute to ongoing efforts to study meteor showers can check out http://skyandtelescope.com/observing/objects/meteors/article_102_1.asp for instructions on how to report observations of meteors. More information about the Perseid shower is available at http://skyandtelescope.com/observing/objects/meteors/article_937_1.asp.
While you wait for meteors to flash across the sky, you can enjoy the spectacle of brilliant orange Mars in the south. The fiery red planet will again double in brightness during August. Rising in the east-southeast around 10 p.m. local time at the beginning of the month and by 9 p.m. at midmonth, Mars will eventually begin to appear during bright evening twilight. Finally on Aug. 28 it will be at opposition -- opposite the sun in our sky and therefore visible all night as it crosses the southern sky. It will far outshine everything except the moon.
This happens every 15 years or so when we pass Mars in our smaller, faster orbit, but this time is special. On Aug. 27 at 4:51 CDT (9:51 Universal Time), Mars will be slightly closer to us than it has ever been in recorded human history. This is because its closest approach to Earth almost coincides with its closest approach to the sun.
Saturn will rise in the east-northeast around 3 a.m. local time by midmonth in the constellation Gemini the Twins with its major stars Castor and Pollux. The cluster of bright stars in the nearby constellation Orion the Hunter will add to the display in the southeast as morning twilight begins.
Mercury will be very low above the western horizon after sundown during August, setting an hour after the sun to clear the way for Mars. Mercury will reach its greatest elevation on Aug. 14, but you may need binoculars to find it in the bright evening twilight.
As if to avoid upstaging the splendor of Mars, brighter Venus and Jupiter will pass behind the sun during August.
Viewing information and graphics are available at http://www.space.com/spacewatch/.
The moon will be at first quarter on Aug. 5, full on Aug. 12, at third quarter on Aug. 20 and new on Aug. 27.