Tehachapi Sky Watch
Illustration Courtesy of NASA
By: Bill Hawkins, Tehachapi News Columnist
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Posted by editor Tue Nov 30, 1999 00:00:00 PST
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0 responses 0 comments Perseid Meteor Shower Peaks — Martians in Distress!
August is often called “Meteor Month” because the best meteor shower of the year occurs in August, and it's warm enough in the wee hours of the morning for meteor-watching to be enjoyable.
As the earth moves around the sun, it does not move through “empty space.” Interplanetary space is strewn with gas, dust, sand, and rocks. Most of the original debris has been swept up by the planets over the last four billion years, leaving pretty clear sailing for Spaceship Terra. However, there's enough left to provide the occasional meteor each night.
The cause of periodic meteor showers, however, is comets. Comets are large, dirty snowballs that orbit the sun. As comets pass the sun, their “snow” evaporates — violently — spewing a tail of gas and dust behind them. After a number of passes, the ices are gone and the dirt and rock that those ices held together are free to float their separate ways.
These new “meteoroids” do not, however, stay tightly packed forever. Free to pursue their own paths, continual collisions with each other causes minor changes in their orbits. Some particles move closer to the sun and some move a bit further away. Thus, some speed up and some slow down. As a result, the dust and rock of the comet spreads out along the entire length of the comet's orbit. If the earth intersects that orbit and passes through the comet's dust, we have a meteor shower.
It would take forever for the material in the comet's orbit to spread itself out completely evenly. So naturally, there are sparser areas and denser areas. When the earth passes through a sparse area, we see a disappointing number of meteors; but if we pass through a very dense area, we can have a “meteor storm” in which meteors are counted in numbers per second! Most meteor showers have been tracked for a long time (in human terms), and thus a reliable average number of meteors per hour can be predicted.
Meteor showers are named for the point in the sky from which they seem to originate. If you were to map every meteor seen during a meteor shower, you would see that they seem to come from a common point (more or less). This is very much like the appearance of rain coming at you in a fast-moving car. This common point lies within a certain constellation, or near a bright star, for which the shower is named.
The grandaddy of all meteor showers is the Perseids, which radiates from the constellation Perseus (PURR-see-us), the Greek mythic hero. These meteors are known to come from the comet Swift-Tuttle and peaks this year on the night of August 12/13. This year the moon will by dark and the Perseids should be splendid, with meteors appearing every minute on average, and occasionally twice that rate.
Another important — and inconvenient — point about meteor showers is that they are best viewed in the pre-dawn hours. This is because the highest part of the local sky is headed directly into the path of the earth's orbit, increasing the number of collisions and the collision speed of the meteors, which is directly related to their brightness. So if you can get to bed around sunset on Sunday evening (say, a little warm milk and brandy), you can enjoy the meteor shower and still be lucid enough at work on Monday.
Manned Space Watch
Space Shuttle Atlantis is preparing for launch on Tuesday to add a truss to Space Station Alpha.
Space Probe Watch
NASA's Spirit and Opportunity robot rovers on Mars have been assailed by a huge dust storm. The dust is obscuring the sky, depriving the solar panels of sunlight and thus vital energy for the rovers. But the real crisis it that dust is piling up on those precious panels — and there's no one up there to dust them off! If the wind doesn't blow them clean, this could be the end of the line for the little mechanical critters. On the up-side, their missions were to have lasted three months, yet they've performed excellently for well over three years! Though their demise will certainly warrant an “Aw, shucks!” it'll also warrant a grand celebration of their achievements.
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