On This Date in History: When Lewis Swift of Marathon New York discovered a comet on July 16, 1862 he wrote that he observed a bright telescopic object. However, he did not report it because he thought that he was simply observing the comet Schmidt. Three days later, at the Harvard College Obervatory in Cambridge, Massachusetts, Horace Parnell Tuttle saw the same object, determined it was headed in a northward trajectory and made an official report. Well, Swift caught wind of the announcement and realized that Tuttle’s comet was his comet and so he made an announcement so that he might get credit for making the discovery first.
As it turns out, a bunch of people saw the comet. Thomas Simmons observed on July 19 from Albany, New York that, when first seen it appeared as a nebula considerably condensed at the centre, the light being intense enough to be easily observed when the wires of the micrometer were illuminated.” Later in July, a whole bunch of astronomers made similar observations. The astronomical community then set out to determine if it was indeed a new comet or the reappearance of one that had been seen before. The looked to the 1737 Kegler comet and the 1750 comet Wargentin. While there were similarities, most agreed that this was indeed a new comet. It became known as the Swift-Tuttle comet which I suppose was a Solomonesque solution to the question of whom to give credit for its discovery. After much calculating, the general consensus was that the period of the comet was 120 years. So, in 1982, the earth breathlessly waited for the comet Swift-Tuttle.
Brian G. Marsden in 1971 had been studying the comet and made two predictions and studying the observational history of Swift-Tuttle. One was that if the definitive orbit suggested came about based on the 1750 comet, then it would arrive in 1981. But, he had also hypothesized that Swift-Tuttle had some things in common with the 1737 comet. In the early 1990′s, Marsden published a new prediction based on the 1737 comet and, ff that rang true, then 1992 would be the date. As it turns out, the 1992 date was correct. But, some astronomers suggest that the 1862 calculations were not wrong, but instead, the comet had changed. Apparently, when a comet streaks through space, it loses particles and when it zips around the sun, part of it is vaporized assymetrically which, in turn, can alter it’s orbit in an unpredictable manner. With the 1992 observations in hand, data suggests that the comet Swift-Tuttle is identical to the 1737 comet Kegler. So, maybe neither Swift or Tuttle discovered anything new.
The trail of debris left behind a comet as it travels through its orbit doesn’t blow away as there is no wind in space. So, when the earth goes through its annual orbit and moves through a particular old trail of a comet, then it runs into that debris. When it does, the small suspended particles from the old comet trail pass through the earth’s atmosphere and burn up producing streaks of light to the earth-bound observer. We call them shooting stars or, more properly, meteors. When there is a flurry of meteor activity then it is referred to as a meteor shower. Because the earth moves in a predictable orbit then one can predict each year when it will pass through the trail of a given comet. To identify each meteor shower, the part of the sky, determined by the zodiac constellations, where the majority of meteors can be seen is used. In the case of the comet Swift-Tuttle, that area is constellation Perseus; hence, it is known as the Perseid Meteor Shower.
The earliest recording of the observation of the Perseid Meteor Shower dates back to around 36 AD in China. It has been recorded periodically throughout history and annually since 1862. The rate of meteors varies greatly from year to year but is highest in the few years directly after the comet’s passage. While it’s debatable if Swfit and Tuttle really discovered a new comet, their observations did for the first time link a comet with meteor activity.
Part of the variance in the intensity of meteor activity with the perseids appears to be due to an inconsistent mass distribution in the Perseid stream, most likely due to the earth encountering variations in the orbit of Swift-Tuttle over 2000 years. While the perseids always come in early to mid August, the brightest, densest concentration of observation tends to vary. In 1953, the most frequent and brightest observations came Aug 8-12. In 1956, the greatest display occured on Aug 6-7. All of the studies show that there is an irregular mass distribution in the Perseid Stream. This year, on this date, the Perseid Meteor Shower is expected to be at its height. Tips for the Perseid Meteor Shower are to expect 50-80 meteors per hour near the constellation Perseus on August 12/13. According the Sky and Telescope, this should be a good year for observing for the simple fact that it’s the first moonless sky for the peak of the perseids since 2007.
While the comet Swift-Tuttle last passed by 18 years ago, filaments of meteorites shed by the comet long ago may be a factor this year. Sky and Telescope suggests that particles from the comet’s passage in 441 and 1479 may liven up this year’s display. National Geographic also suggests we may be running into a “meteor clump.” While the Perseids have been seen since July, the best time to observe in the Northern Hemisphere tonight will be between 11pm and dawn. Look to the northeast. The perseids will appear to streak outward from the edge of Perseus and Cassiopeia. It’s best if you can get away from urban settings and find a dark, rural area where the sky is wide open and unobstructed. If you miss it due to cloud cover or other obligations, you can still see the Perseids over the next few days. The rate will probably fall by a quarter or a half from the peak for the next two days. The latest a Perseid has been seen has been August 24. Don’t worry about getting hit on the head. Most meteorites are about the size of a pebble, become visible at 40 to 75 miles above the earth and disintigrate 30 to 60 miles above.
Weather Bottom Line: Hopefully, you got some rain on Wednesday. Some folks got some pretty good and decent downpours. The frontal boundary that got close enough to help focus activity in our area is lifting north. We may have an outlaw afternoon t’storm pop up but chances will go down for the next few days until a frontal system approaches late Saturday. It should stick around enough to provide at least scattered activity on Sunday as well as Saturday afternoon and night. I don’t think that it’s going to move through too far so it will only knock about 8-10 degrees off the mercury. The rain activity will go off the board on Monday and Tuesday but that front will most likely be drawn back up on Wednesday and reintroduce rain chances.