Sunday, August 8, 2010

Perseid meteor shower

After midnight in the early morning hours of either Thursday, August 12 or Friday, August 13 will be the best time to view the annual Perseid meteor shower.  It's just after the new moon on the 9th so the skies will be nice and dark (assuming it's clear - not always a sure bet in the frequently-cloudy Hudson Valley).  These dates are only when the shower peaks, by the way, any meteors seen between July 24 - August 24 are generally Perseids as well.

The Perseids are named since they radiate from the portion of the sky where the constellation Perseus is located.  Perseus rises in the northeast around 11 pm and gets progressively higher in the sky after midnight in the early morning hours.

The Perseids exist because the comet Swift-Tuttle has left a trail of debris around that part of the Earth's orbit which are swept down into the Earth's atmosphere leaving a glowing trail of their own self-destruction.  Virtually all of these particles are dust-sized grains and disintegrate without leaving a meteorite to strike the Earth's surface.

Swift-Tuttle was discovered in 1862 and returned in 1992.  Next time will be in 2126 after we're all dead and gone.  The interesting thing about Swift-Tuttle is that it's big (27 km across) and crosses Earth's orbital plane.  If it ever struck, we'd all become extinct (the asteroid that knocked out the dinosaurs was only 10 km across).  Not to worry, while the 2126 pass will be close, leading to Swift-Tuttle being a bright, spectacular comet, it's not close enough to hit us (and we'll all be dead and gone, anyway, remember?).

So why are meteor showers best after midnight?  Look at the diagram below:

Which position, A or B, will show the debris entering the Earth's atmosphere best?  Position A is just after sunset on the trailing side of the Earth while position B is before sunrise (after midnight) on the leading side of the Earth in its orbit around the Sun.  At position B, we're plowing right into the debris field left by comet Swift-Tuttle and the meteor shower will be at its best.  Continuing on in that direction is the constellation of Perseus - the radiant of the meteor shower.

Even better, earlier in the evening, there will be a nice conjunction of planets visible in the western sky from about 9 pm or so, when it gets dark, until around 10 pm when they set.  Venus, Mars, and Saturn will be easy to find as they're clustered around bright Venus just above the crescent waxing moon.

As an added bonus, a nice, bright Jupiter will be visible in the eastern sky after midnight (it will be the brightest "star" in the sky over there).  Perseus will be left of Jupiter if you're facing east and below the W of Cassiopeia.

So, if it's clear next Wednesday or Thursday, pull an all-nighter (those get increasingly difficult with advancing age, don't they?) and lay out in your lawn chair and enjoy the celestial show.

No comments:

Post a Comment