Kids Research Express

Open Cluster, or galactic cluster, group of associated stars that travel together through space. Astronomers have cataloged about 1200 open clusters in the earth’s galaxy, each containing from ten to many hundreds of stars (see Milky Way ). Astronomers have also discovered hundreds of open clusters in other galaxies. The stars in a galaxy usually orbit in a plane around a common center, and almost all open clusters lie close to the plane of the galaxy in which they’re located. Clusters range from about 5 light-years to about 70 light-years in diameter. Often a thin, misty light, caused by reflection of starlight off the cosmic dust and gas in the cluster, envelops an entire cluster. Open clusters are classified by the number of stars in them and by the degree to which the stars are concentrated toward the center of the cluster. All clusters in the same class are roughly the same size. The stars in an open cluster are usually relatively young, and the cluster is considered the same age

Great Orion Nebula or Orion Nebula, or M 42, diffuse nebula , or cloud of gas and dust, located in the constellation Orion. With its brightest parts having an apparent magnitude (a measure of brightness as seen from the earth) of 4.0, the Great Orion Nebula can be seen with the unaided eye as part of Orion’s sword, which hangs from his belt. The Great Orion Nebula looks like a star when it is seen with the unaided eye, but even a small telescope reveals its cloudy nature. The entire Great Orion Nebula as seen from the earth is about 60 arc minutes wide, or about four times as wide as the full moon. The Great Orion Nebula is about 1500 light-years from the earth and it is about 30 light-years in diameter. Unlike some diffuse nebulae, which are visible only because they reflect the light of nearby stars, the Great Orion Nebula not only reflects light, but it also emits light. Emission nebulae like the Great Orion Nebula are so huge that they provide enough gas and dust to create new sta

Orion (astronomy), constellation located on the celestial equator east of Taurus . It is an oblong configuration with three stars in line near its center. It is represented on pictorial charts as the figure of Orion, the hunter in Greek mythology, standing with uplifted club. Three bright stars represent his belt and three fainter stars aligned south of the belt represent his sword. Alpha (a) Orionis, or Betelgeuse , is located in the left corner of the oblong, corresponding to Orion's shoulder. Beta (β) Orionis, or Rigel , is diagonally opposite Betelgeuse. A nebula surrounding the three stars marking Orion's sword is one of the most conspicuous bright nebulas in the heavens. In Greek mythology, Orion is the handsome giant and mighty hunter, the son of Poseidon, god of the sea, and Euryale, the Gorgon. Orion fell in love with Merope, the daughter of Oenopion, king of Chios, and sought her in marriage. Oenopion, however, constantly deferred his consent to the marriage, and O

Equator, in astronomy, the great circle in which the plane of the equator of the earth intersects the celestial sphere. The celestial equator is the line from which the declination of stars and planets is measured. See Ecliptic .

Magellanic Clouds, small, irregular galaxies that lie relatively near the Milky Way galaxy. The Large Magellanic Cloud (LMC), in the constellation Dorado (the Goldfish), and the Small Magellanic Cloud (SMC), in the constellation Tucana (the Toucan), are visible to the unaided eye in the southern hemisphere and as far north as 16° North latitude. They became known in Europe through descriptions made in 1521 by the Portuguese navigator Ferdinand Magellan, after whom they were named. The LMC lies about 150,000 light-years away from our sun, and the SMC lies about 173,000 light-years away. In the early 1980s, another galaxy, called the Mini Magellanic Cloud (MMC), was determined to lie about 20,000 light-years beyond the SMC, in the same line of sight. Apparently it was torn from the SMC by a near encounter with the LMC about 200 million years ago. A supernova was observed in the LMC in 1987.

Cassiopeia (astronomy), northern constellation , near the celestial pole. It is distinguished by a group of five stars, of second to fourth magnitude , in the form of a rough letter W. The brightest supernova on record appeared in the constellation in 1572 and was observed by the Danish astronomer Tycho Brahe . Brighter than the planet Venus, for about 16 months Cassiopeia was visible to the naked eye even at noon. It is named for the mythological Ethiopian queen Cassiopeia, the mother of Andromeda .

Transit, passage of one heavenly body over the disk of another, as of Mercury or Venus over the disk of the sun, or of a satellite over its primary. A transit of Mercury or Venus can take place only when either planet passes the sun at the time the sun is near one of the nodes of the planet; that is, when Venus or Mercury is in inferior conjunction, or is closer to earth than to the sun. The transit of Venus was first recorded in 1639. In 1679 the English astronomer Edmond Halley pointed out that these transits could be used to determine the distance of the sun. Usually two transits of Venus occur within 8 years of one another; then, after a lapse of 105 or 122 years, another two transits occur within 8 years. Transits of Mercury occur about 13 times in each century. The term transit also refers to an instrument for measuring the passage of an object past the local meridian (see Transit Instrument ). Likewise, the passage of an object past the local meridian is called a transit.