August Astronomy

Bright Jupiter sits to the left of the waning crescent Moon, with orange Mercury just below at a respectable magnitude –0.3, 40 minutes before sunrise on the 3rd. Jupiter, Mars, and Mercury stand in a row, low in the east in growing morning twilight, with the crescent Moon to their right on the 4th. Venus, still quite low in the west soon after sunset, hovers above the slender crescent Moon on the 9th. Much higher, the Moon is to the lower right of Saturn at nightfall on the 12th. The Moon will set before midnight and will not spoil the great Perseid meteor shower on the nights of the 11th and 12th. These will be the year’s best “shooting stars.” Neptune, in Aquarius at magnitude 7.8, requires a small telescope to be seen at its opposition.

This month’s highlights: The Perseid Meteor Shower!

On August 11, 12, and 13 comes an annual event that is always worth watching if your skies are clear. It’s the Perseid Meteor Shower, or simply the Perseids. Meteors are particles of dust and rock that appear as streaks of light — “shooting stars” — when they burn up due to friction as they collide with the Earth’s atmosphere. You can see meteors on any dark, clear night, but during a meteor shower the number of meteors increases dramatically.

In the case of the Perseids, the particles are bits and pieces left behind by Comet Swift-Tuttle. Swift-Tuttle circles our Sun once every 133 years. As it does so, it leaves a stream of debris in its wake. Each year in August, the Earth passes through this debris, and we see the result as an unusually large number of meteors — the Perseid Meteor Shower. Most meteors are quite small, like grains of sand or small pebbles, and they burn up completely in the atmosphere. When a meteor is large enough that fragments survive to reach the ground, it can make headlines, like the 50-foot object that entered the atmosphere over Chelyabinsk, Russia, on February 15 of this year.

Watching a meteor shower couldn’t be simpler. All you need are your own two eyes and a dark location away from city lights. A reclining lawn chair is helpful to prevent a stiff neck, though you may find it even more comfortable to stretch out on the ground atop (or inside) a sleeping bag. The best time to observe the Perseids is between midnight and sunrise; that’s when the Earth will be colliding head-on with the meteor stream. You may see as many as 60 meteors an hour from a dark site, and the meteors can appear in ANY part of the sky. Be patient! Many minutes may pass with no activity, then suddenly you will see several meteors in quick succession.

So why do we call this meteor shower the Perseids? It’s due to the fact that all of the meteors in this shower appear to radiate from a point the constellation Perseus. This does NOT mean that you should look near Perseus to see the meteors, however. Not at all! The Perseid meteors can and will appear anywhere and everywhere in the sky. But if you trace the streaks of the Perseids back towards the direction from which they came, they will all appear to have come from the direction of Perseus. The location from which the meteors appear to radiate is called the Radiant of the meteor shower.

August is a good month is which to view several distinctive constellations and asterisms (unofficial star patterns) that appear in the Northern sky. These include the Big and Little Dippers, the large “W” of Cassiopeia, the upside-down “house” shape of Cepheus, the sinuous constellation Draco, the Dragon, and Corona Borealis, the Northern Crown.

Finally, August 6 marks the one year anniversary of the landing on Mars of the Mars Science Laboratory, better known as the Curiosity Rover. In its first year, Curiosity has confirmed that there was once water of the surface of Mars.

August 2013
by Bob Berman, as featured in
The Old Farmer’s Almanac


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