Sign Up for e-mail newsletters. Get breaking space news and the latest updates on rocket launches, skywatching events and more! Contact me with news and offers from other Future brands. Receive email from us on behalf of our trusted partners or sponsors. Thank you for signing up to Space. You will receive a verification email shortly. There was a problem. If it's time for a meteor shower, you won't need a telescope, binoculars, or a high mountain to have a "star gazing" party.
You might need a warm sleeping bag and an alarm clock to wake you in the middle of the night. But then just lying down in your own back yard will put you in the perfect spot to enjoy a great show. A meteor is a space rock—or meteoroid—that enters Earth's atmosphere. As the space rock falls toward Earth, the resistance—or drag—of the air on the rock makes it extremely hot.
What we see is a "shooting star. Why would Earth encounter many meteoroids at once? Well, comets, like Earth and the other planets, also orbit the sun. Unlike the nearly circular orbits of the planets, the orbits of comets are usually quite lop-sided.
As a comet gets closer to the sun, some of its icy surface boils off, releasing lots of particles of dust and rock. Small particles blown into the atmosphere lit the night sky for several days. No meteorite was ever found, and for years many scientists thought the devastation was caused by a comet. Now, the prevailing theory holds that a meteor exploded just above the surface. A similar event occurred over Chelyabinsk, Russia , when a meter rock exploded 12 to 15 miles above the Earth's surface on Feb.
Although the Russian event brought into focus the possible danger Earth could suffer from space rocks, most meteors don't cause nearly as much damage. Still, NASA and other entities keep careful track of all asteroids visible from Earth, and are actively engaged in discovering as many asteroids as possible — especially the ones that are larger and would pose more of a theoretical threat to Earth.
Asteroid orbits are plotted and tracked to see if they will intersect with Earth in the future. In ancient times, objects in the night sky conjured superstition and were associated with gods and religion. But misunderstandings about meteors lasted longer than they did about most other celestial objects. Meteorites the pieces that make it to Earth were long ago thought to be cast down as gifts from angels. Others thought the gods were displaying their anger. As late as the 17th century, many believed they fell from thunderstorms they were nicknamed "thunderstones".
Many scientists were skeptical that stones could fall from the clouds or the heavens, and often they simply didn't believe the accounts of people who claimed to have seen such things. In , a fireball exploded over Connecticut, and several meteorites rained down. By then the first handful of asteroids had been discovered, and a new theory emerged suggesting meteorites were broken bits off asteroids or other planets.
A theory that still holds. The largest meteorite recovered in the United States fell in a wheat field in southern Nebraska in Witnesses saw a giant fireball in the afternoon that some said was brighter than the sun.
The meteorite was found buried 10 feet 3 meters deep in the ground. It weighed 2, lbs. The most famous meteorite crater in the United States is misnamed Meteor Crater. It's in Arizona, and it's huge. By Francis Reddy. In this wide-angle view, Orion the Hunter top right hovers above Sirius bottom right , the brightest star in the sky. Those spending enough time under the night sky eventually will see a "shooting star," a streak of light that flashes across the sky in less than a second.
This is a meteor, a glowing trail caused by the incineration of a piece of celestial debris entering our atmosphere. Many meteors are quick flashes, but some last long enough for us to track their brief course across the sky. Now and then, a meteor truly will light up the night, blazing brighter than Venus — and although rarely, even brighter than the Moon — leaving in its wake a dimly glowing trail that may persist for minutes.
Under a dark sky, any observer can expect to see between two and seven meteors each hour any night of the year. These are sporadic meteors; their source bodies — meteoroids — are part of the dusty background of the inner solar system. Several times during the year, Earth encounters swarms of small particles that greatly enhance the number of meteors. The result is a meteor shower, during which observers may see dozens of meteors every hour. Concentrations of material within the swarms may produce better-than-average displays in some years, with rates of hundreds per hour.
And every now and then, we're treated to a truly spectacular display in which thousands of visible meteors can be seen for a brief period. These are referred to as meteor storms. The meteors that appear during a meteor shower seem to radiate from one point in the sky. This illusion is an effect of perspective, just as a roadway seems to converge in the distance. Usually, meteor showers take the name of the constellation from which the meteors appear to radiate.
For example, during the Perseid shower in August, meteors seem to streak from a point in the constellation Perseus. The science of meteor astronomy began in , when a storm of 60, meteors an hour shocked the world. By the s, it had become clear that many meteor showers were annual — including the normally placid Leonids, which produced the big storm — and that they were somehow related to comets.
Astronomers now consider comets to be "dirty snowballs" consisting of a mixture of dust and frozen gases. A comet becomes visible only during its closest approach to the Sun, when areas on the comet's icy surface become warm enough to evaporate. The resulting jets of evaporating gases carry with them any solid matter mixed with the original ice. At each pass near the Sun, the comet ejects a stream of material. The particles composing the stream orbit the Sun in slightly different paths than the source comet.
Each particle receives small accelerations from forces other than gravity, and these orbits become increasingly modified over time. The ejected streams become more diffuse with age and lose their individual identities. Concentrated initially near the comet, the debris diffuses along each stream's orbit and eventually forms a thin band of material that Earth encounters every year.
A meteor shower occurs on the date in the year when Earth passes nearest to the band of material associated with a comet's orbit. Most of the meteors seen during one of the annual showers arise from fluffy particles not much larger than sand grains. As a particle enters Earth's atmosphere, it collides with gas atoms and molecules.
The particle becomes wrapped in a glowing sheath of heated air and vaporized material boiled off its own surface. Meteors become visible at altitudes between 50 and 75 miles 80 and kilometers , with faster particles typically shining at greater heights. Many of the faster, brighter meteors may leave behind a train — a dimly glowing trail that persists for many seconds or, more rarely, minutes.
Larger debris may create a fireball — a spectacular meteor bright enough to outshine even Venus. Occasionally, a fireball will fragment; this event is accompanied by bright flares and even "sparks" thrown a short distance from the meteor's main trail. Such a fireball is called a bolide. The best way to enjoy a meteor shower is to dress warmly, set down a blanket or lawn chair at a dark site, get comfortable, and watch the stars.
0コメント