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Planetary News: Near Earth Objects (2007)Don't Miss a Great Perseid Meteor Shower and a Total Lunar EclipseBy Bruce Betts
Meteor showers can be big fun to watch. The Perseid meteor shower is traditionally one of the best of the year, and this year its peak coincides with New Moon, making this year an ideal one to go out and look up. The Perseids are expected to peak late on August 12 and very early August 13. But, if you can't go looking right at the peak, or if it is cloudy or daylight where you live, don't worry: the Perseids are spread out over a multi-week period and have increased activity for a day or two before and after the peak. Meteors are the streaks of light formed when bits of material hit Earth's atmosphere at very high speeds -- 11 kilometers per second (25,000 miles per hour) to 72 kilometers per second (160,000 miles per hour)! Most of the particles are small: dust- to sand-sized bits. But, because they are going so fast, they still pack a lot of kinetic energy. As the particles hit the upper atmosphere, they ionize the gases they are passing through, which causes them to glow. What we see from the ground are streaks of light ranging from quick and short, to long and bright, depending on the size, velocity, and orientation of the particle as it hits the atmosphere. Particles are hitting Earth's atmosphere all the time, so on any night -- with enough patience and a dark site -- you can see meteors. But, during certain times each year, we pass through debris streams that have come off comets during their passages around the Sun. The debris streams cause meteor showers: more particles hit the Earth, so we see more meteors. The Perseids are detritus from comet Swift Tuttle, which orbits the Sun every 130 years. From a dark site, the Perseids can yield 60 to 100 meteors an hour near their peak. As a general rule, you can see more meteors later in the night as you rotate around to Earth's leading side going through space. Indeed, for the Perseids, you should see progressively more meteors the later you watch. This will be accentuated by the radiant coming over the northeastern horizon in the mid-evening. What is a radiant, you say? Meteor showers will appear to radiate from one location in the sky, that is, if you draw the lines of meteors back through the sky, they will all intersect in one general location. In the case of the Perseids, this radiant is in the constellation Perseus. For this reason, it will be tough for observers in the southern hemisphere to see the Perseids, since Perseus will be below the horizon. However, those in low southern latitudes may be able to see some Earthgrazers, those meteors that graze the top of the atmosphere causing them to last longer as they travel across the sky. Where in the sky should you look to see the Perseids? Well, you'll tend to get two answers to this question. One is look where it is darkest in your sky. For all but those at uniformly dark sites, this is probably the right answer. For those at a uniformly dark site, you may increase the numbers that you will see by looking about half way between the radiant and the zenith (the point overhead). The key to meteor watching is patience. Relax and stare at the sky. Soon, the "oohs" and "aahs" will start to flow from your lips and from those around you. Upcoming Lunar EclipseWhile we are talking about the night sky, don't miss the total lunar eclipse about two weeks after the Perseids. The lunar eclipse will be visible from throughout most of eastern Asia, Australia, the Pacific Ocean, and the Americas. The Moon will pass through Earth's shadow on August 27 or 28, depending on your time zone. The umbral eclipse (the Moon starts moving into the darkest part of Earth's shadow) will begin on August 28 at 1:51 a.m. and end at 5:24 a.m Pacific Daylight Time (0851 to 1224 Universal Time). You can learn more at Meteor Showers: Where When and How to Look for Them, and you can always keep up with What's Up in the night sky by listening to Planetary Radio. Random Space Fact: a meteor is the streak of light made as a particle enters the atmosphere; a meteorite is an object that made it all the way to the surface from space (few meteors result in meteorites since small particles burn up in the upper atmosphere); and a meteoroid is one of these objects while still in space. |
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