jueves, 4 de abril de 2013

Everything you need to know: Lyrid meteor shower

The annual Lyrid meteor shower is active from about April 16 to 25. In a dark sky, you might see 10 to 20 meteors per hour.

It’s nearly time for the annual Lyrid meteor shower. The shower is active each year from about April 16 to 25. In 2013, new moon comes on April 10. Afterwards, the moon will be waxing and in the evening sky. Full moon falls on April 25, and around that time the sky will be bright with moonlight for much of the night. The short-lived Lyrids peak usually lasts for less than a day, coming yearly on or near April 22. Due to the moon phase in 2013, the predawn hours on April 22 will be best for meteor-watching. At their peak, the Lyrids offer about 10 to 20 meteors an hour. So heads up! It’s nearly Lyrids meteor-watching time. In 2013, the Lyrids are expected to produce the most meteors in the dark hours before dawn on April 22. The big and bright waxing gibbous moon will be interfering with the Lyrid display until the hours before dawn. So plan to get some sleep, and set your alarm for a few hours before the April 22 sunup. Meteor-watching aficionados will be on the lookout anyway. Meteor showers are notorious for defying the most careful predictions, and the Lyrids stand as no exception. An outburst of Lyrid meteors is always a possibility, though none is predicted for this year. For instance, American observers saw an outburst of nearly 100 meteors per hour in 1982. Also in the 20th century, around 100 meteors per hour were seen in Greece in 1922 and from Japan in 1945. So you never know . . . The Lyrid meteor shower is among the oldest of known meteor showers, with records going back for some 2,700 years. Apparently, the ancient Chinese observed the Lyrid meteors “falling like rain” in the year 687 BC.

A fireball meteor falling earthward, courtesy of NASA/George Varros

 If you trace the paths of all the Lyrid meteors backward, they are seem to radiate from the constellation Lyra the Harp, near the brilliant star Vega. However, this is only a chance alignment, for these meteors burn up in the atmosphere about 100 kilometers – or 60 miles – up. Vega lies trillions of times farther away at 25 light-years. The star Vega resides quite far north of the celestial equator, so for that reason the Lyrid meteor shower favors the Northern Hemisphere. At mid-northern latitudes, Vega sits low over the northeastern horizon around 10 p.m. Afterwards, Vega soars upward during the nighttime hours and reaches its highest point in the sky around dawn. As a general rule, the higher that Vega climbs into the sky, the more meteors that you’re likely to see. That’s why the greatest numbers of meteors generally fly in the dark hours before dawn.

Lyrids and others via NASA/MSFC/D. Moser

Comet Thatcher: Source of the Lyrid meteor shower

Every year, in the later part of April, our planet Earth crosses the orbital path of Comet Thatcher (C/1861 G1), of which there are no photographs due to its roughly a 415-year orbit around the sun. Comet Thatcher last visited the inner solar system in 1861, before the photographic process became widespread. This comet isn’t expected to return until the year 2276. Bits and pieces shed by this comet litter its orbit and bombard the Earth’s upper atmosphere at 177,000 kilometers (110,000 miles) per hour. The vaporizing debris streaks the nighttime with swift-moving Lyrid meteors. If Earth passes through an unusually thick clump of comet rubble, an elevated number of meteors could be in store.

  How to watch the Lyrid meteors

Fortunately, you don’t need any special equipment to watch a meteor shower. Simply find a dark, open sky away from artificial lights. Lie down comfortably on a reclining lawn chair, and look upward. Although the moonlight is sure to wash out a good number of Lyrid meteors in 2013, some Lyrids may be bright enough to overcome the moonlit glare. Another beautiful feature of the Lyrids to watch for … about one quarter of these swift meteors exhibit persistent trains – that is, ionized gas trails that glow for a few seconds after the meteor has passed. Bottom line: Remember that the Lyrids aren’t the year’s best meteor shower. In the Northern Hemisphere, that distinction often goes to the Perseids in August. But the Lyrids do offer 10 to 20 meteors per hour at their peak in a moonless night; in 2013, that means before dawn on April 22. And remember that, like all meteor showers, the Lyrids aren’t altogether predictable. In rare instances, they can bombard the sky with up to nearly 100 meteors per hour.

source and credit a earthsky