Jimmy Westlake: Summer meteor showers
July 24, 2012
Steamboat Springs — If you've noticed an increase in the number of shooting stars in recent nights, there's a good reason. This month's annual Delta Aquarid meteor shower is increasing in activity as we get closer to its peak on Sunday morning. Other minor showers, like the Kappa Cygnids and the Capricornids, also are throwing in a few meteors.
A meteor shower is named for the constellation from which the meteors seem to radiate. So we have, for example, the August Perseids, which radiate from the constellation of Perseus; the December Geminids, which radiate from the constellation Gemini; and this month's Delta Aquarids, which seem to spring from near the star Delta in the constellation Aquarius.
Our annual meteor showers are produced when the Earth plows through the path of an old comet and collides with leftover dust particles in the comet's wake. The parent comets for most of our major annual meteor showers have been well established. For example, the May Aquarids and the October Orionids are produced when Earth crosses the orbit of Halley's comet, twice each year. July's Delta Aquarid shower is unique in that it is the only strong shower whose parent comet is unknown. Either the parent comet was pulled into a different orbit long ago after a close pass by one of the outer planets, or it met with some catastrophic end. The primary suspect is periodic comet 96P/Machholz 2, which crumbled into pieces as astronomers watched it round the sun in 1994, but this conclusion is far from certain. For the present time, the source of the July Delta Aquarid meteors remains a mystery.
To watch the Delta Aquarid meteor shower, you'll need to set your alarm for about 3 a.m. Sunday, or else (like me) just stay up all night long. The Aquarius constellation doesn't rise until about 11 p.m. Saturday night, so don't expect to see any Delta Aquarids before then. Aquarius is at its highest in the southern sky at about 4 a.m., so this will be the best time to watch. The meteors will seem to dart in every direction, but their paths all will start from near the star Delta Aquarii, just above the bright star Fomalhaut. You might see one or two meteors every five minutes, on average. It's more of a sprinkle than a shower, really. Consider the Delta Aquarids just a warm-up for the granddaddy of all meteor showers, the Perseids, coming in August, which can produce more than one meteor per minute.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Westlake’s astrophotography website at http://www.jwestlake.com.