Meteor Shower

Meteor Shower
I INTRODUCTION
Meteor Shower, certain time of the year when meteors fall in greater numbers than usual and seem to come from specific parts of the sky. Meteors are particles of space dust that enter the earth’s atmosphere and burn up, creating a streak of light in the night sky. Over 120 recognized meteor showers occur during the year. Humans have recorded observations of meteor showers for at least 3000 years. Within the last 50 years astronomers have begun to study meteor showers with photography, video, radio, and radar equipment. Observations of meteors and meteor showers provide important information about the distribution of matter in the solar system and the origins of comets, asteroids, and other small bodies in the solar system.

II METEOR SHOWERS AND THEIR ORIGINS
A meteor shower happens when the earth moves through a belt of particles in space. Many such streams of particles orbit around the sun. In some cases the orbit of the particle stream is very similar to that of a comet or asteroid. If a belt of particles and an asteroid or comet share an orbit, the asteroid or comet is called the parent body of the particle stream and the meteor shower. A parent body sheds material and gradually breaks up, leaving a trail of dust and rock that follows in the parent body’s orbit and becomes a particle stream that can cause a meteor shower.
Most parent bodies are comets, because most asteroids orbit the sun between the orbits of the planets Mars and Jupiter and never cross Earth’s orbit. Some showers, such as the Geminids, are related to asteroids with orbits that cross the earth’s orbit. Some meteor showers have no current parent body. Astronomers assume that the particle streams that cause these showers came from comets or asteroids that have broken up completely or have changed orbits.
Astronomers can associate a comet with a meteor shower by studying whether the period of the comet, or the time it takes to travel around the sun, corresponds to the amount of time between the most intense years for the meteor shower. Halley’s Comet has two associated meteor showers: the Eta Aquarids and the Orionids. Both showers showed higher rates of meteors per hour when the comet passed near the earth in the 1980s. The Leonid meteor shower’s parent body is comet Temple-Tuttle. The comet has a period of about 33 years and it has produced very intense storms when it has passed near the earth. Other meteor showers, including the Lyrids, seem to come from particle streams that have the same orbit as a comet but do not show much change in intensity when the comet is close to the earth.
The characteristics of a particular stream of particles determine what the meteor shower will be like. The gravitational forces between the particles and the planets and the sun, as well as the interaction of the stream with energy from the sun spread out and change the stream over time. Streams of particles tend to get wider as they get older. The width of the stream affects how long a meteor shower lasts—wider particle streams cause longer meteor showers. The gravitational pull of the sun, the earth, and other bodies in the solar system may cause streams to get farther away from or closer to the earth’s orbit, causing some known meteor showers to stop and new meteor showers to begin.
The position of a meteor shower’s parent body also affects the particle stream and the meteor shower. Comets begin to shed matter as they approach the sun. By the time a comet is as close to the sun as the earth is, it often has a long tail of gas and dust. If the earth intersects a particle stream soon after its parent comet has passed, the resulting meteor shower is often much heavier than usual.
It may take hours for an observer to determine that a meteor shower is in progress. Not all meteors are part of a shower. Space dust enters the atmosphere from sources other than structured streams of particles. Even during a shower, meteors may fall at a rate of less than ten per hour. Astronomers know that a succession of meteors belong to a shower when they all seem to come from the same point in the sky, called the radiant. The position of the radiant depends on the speed and direction of both the earth and the particle stream as they collide. A meteor shower’s radiant gradually moves during the course of the shower, but most showers take their name from the constellation nearest to the radiant when the maximum rate of the shower occurs.
The radiant of a meteor shower is actually an optical illusion. Meteors enter the earth’s atmosphere over a large area, but they begin to burn up so far above the observer that their trails seem to lead back to one common point, just as parallel railroad tracks seem to meet at the horizon.

III HISTORY OF METEOR SHOWER OBSERVATION
Chinese, Hebrew, Greek, and Roman records of meteor showers date back about 3000 years. The most ancient records of meteor showers show that people interpreted the showers as magical or religious events. Ancient Greeks and Romans thought meteor showers were weather-related, like lightning and rain. During the 18th century many scientists, including American astronomer David Rittenhouse, began to favor the idea that meteor showers had their origin in space.
Many scientists still believed that meteors were weather-related or caused by some phenomenon on the earth and did not accept that meteors came from space until the Leonid meteor storm in 1833. In that storm, observers noticed that the meteors all seemed to come from one place in the sky (see Leonids). This is an effect of perspective, but proved that the meteors originated beyond the earth’s atmosphere.
American astronomer Charles P. Olivier and British astronomer William F. Denning helped pioneer modern visual scientific studies of meteor showers in the beginning of the 20th century. American astronomer William Lewis Elkin obtained the first photographs of meteors during the Perseid and Leonid showers in the first years of the 20th century. British astronomers James Stanley Hey and G. S. Stewart studied meteor showers with radar. They projected radio waves into the sky during a meteor shower and recorded the radio waves as they bounced back from the meteors. The results of radar observations of meteor showers are very similar to the results of visual observation.

IV MODERN STUDY OF METEOR SHOWERS
Meteor shower observers often study showers with the unaided eye. Observers record the number of meteors that fall each hour, the path each meteor seems to follow in the sky, how long each flash lasts, and the brightness and color of each meteor. Amateur observers who record this data provide a great deal of the information that scientists have collected about meteor showers. Occasionally observers even discover new showers. Records of rises and falls in shower activity can give astronomers an idea about the period of its parent body.
Meteors leave electrons behind as they burn up in the earth’s atmosphere. These electrons can reflect radio waves. During a meteor shower, a radio receiver can sometimes receive signals from radio stations or other radio sources up to 2000 km (1200 mi) away, an unusually long distance. The meteor observing technique called radio forward scatter relies on a radio receiver that can detect radio waves reflected by meteors from a distant radio transmitter. Observers tune the receiver to a particular radio station that is too far away for the receiver to get normally. The signal that results when a meteor reflects radio waves from the transmitter is audible, so an observer can count the number of signals he or she hears. The number of audible signals equals the number of meteors reflecting radio waves. Computers and other devices can also count the number of signals that meteors reflect. Statistically, the results of radar observations of meteor showers are very similar to the results of visual observation.
Meteor observations with radar work much the same way that observations with radio forward scattering observations do. With radar, the receiver and transmitter are at the same place. Both methods provide numbers of meteors per hour, without the visual observer’s dependence on a clear, dark sky.
Astronomers can determine the orbit of the particle stream that creates a meteor shower by finding out the radiant of the shower and the speed of the meteors. Observers must record meteors with cameras or video cameras. Photographic and video observations can detect meteors that are dimmer than those that the unaided eye can detect. They also provide information about the mass and speed of the meteors that simple visual observation cannot.
Some of the meteors in a meteor shower fall all the way to the surface of the earth as tiny particles of dust. Astronomers have collected dust that falls to the earth from space, but scientists cannot distinguish dust from meteor showers from other cosmic dust. Experiments aboard the United States space shuttle occasionally catch very bright meteors on video, but none of these have been connected with known showers.

Contributed By: David D. Meisel

Curtis Institute of Music, The

Curtis Institute of Music, The, private, coeducational institution in Philadelphia, Pennsylvania that offers undergraduate, graduate, and professional education in music. The institute, established to train talented young musicians, was founded in 1924 by Mary Louise Curtis Bok, the wealthy daughter of publisher Cyrus H. K. Curtis. The school operates under a charter granted by the state of Pennsylvania, with funding from two endowments left by Bok after her death in 1970. Students are admitted on the basis of their performance during a competitive audition. Once admitted, they receive a full-tuition scholarship.
The Curtis Institute offers a bachelor of music degree and a master of music degree in opera. It also offers a program leading to a professional studies certificate in opera. Training includes private instruction with professional musicians, diction coaching for singers, chamber music sessions for instrumentalists, master classes with visiting artists, and opportunities for solo and ensemble performance. Undergraduates are also required to study a core curriculum of English composition, literature, and the history of Western civilization. Once students have completed these classes they can enroll in courses at the University of Pennsylvania at no cost.
The institute occupies four mansions on Rittenhouse Square in downtown Philadelphia. These buildings house classrooms, a library, an art collection, administrative offices, a 250-seat auditorium, and an orchestra library, containing the Leopold Stokowski collection of documents and memorabilia. The school has no student housing. Former teachers and directors at Curtis include violinist Leopold Auer, pianist Josef Hofmann, Philadelphia Orchestra conductor and founder of the Curtis Institute Orchestra Leopold Stokowski, and violinist Efrem Zimbalist, Sr.

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