天体和天球及天球坐标精讲.pptVIP

总的来说，天球及天球坐标比较抽象，这需要读者建立时空概念，并有一定的耐心。在本书的以后章节里，它们将是认识天体视位置和视运动的辅助工具。 思考与练习（见书） 第二章结束 * 由于人们对天体认识和理解，在不同历史时期是大不相同的，现代天文学的观测和研究证明了宇宙是物质的，所以目前把天体认为是宇宙间各种星体的总称。包括：恒星（如太阳）、行星（如地球）、卫星（如月亮）、彗星、流星体、陨星、小行星、星团、星系、星际物质等。 * 由于人们对天体认识和理解，在不同历史时期是大不相同的，现代天文学的观测和研究证明了宇宙是物质的，所以目前把天体认为是宇宙间各种星体的总称。包括：恒星（如太阳）、行星（如地球）、卫星（如月亮）、彗星、流星体、陨星、小行星、星团、星系、星际物质等。 * Planets are probably forming along with new stars in these nebulae in Sagittarius. The type of planet that forms at a particular distance from a star depends on such conditions as the temperature there and the substances—rock fragments, ice crystals, and gases—at that distance. In the solar system, planets composed primarily of rock formed near the Sun, buts its heat drove off ices and gases. Far from the Sun, where temperatures are low, planets retained volatile substances, resulting in worlds composed primarily of gas. (Royal Observatory, Edinburgh) * This nebula (also called Mi or NGC 1952) is a supernova remnant. A dying star exploded, and this beautiful funeral shroud was caused by the gases that were blasted violently into space. In fact, these gases are still moving outward at about 1000 km/sec (roughly 2 million miles per hour). The Crab Nebula is 6300 light years from Earth, and the distance across the nebula is about 6 light years. (Lick Observatory) * This spectacular galaxy (also called NGC 5236) contains about 200 billion stars. The galaxys spiral arms are outlined by numerous nebulae that are the sites of active star formation. This galaxy has a diameter of about 35,000 light years and is at a distance of 12 million light years from Earth. (Courtesy of R. J. Dufour) * Quasars are the most distant and most luminous objects that astronomers have ever seen. At first glance, a quasar is easily mistaken for a faint star. This quasar is thought to be at a distance of 4.8 billion light years from Earth. (Palomar Observatory) 第二章 天体和天球及天球坐标 §2.1天体和天体系统 一、天体概念及主要天体简介 天体概念: 宇宙中所有的星体统称为天体。 主要天体简介（星云、星系、恒星、行星、卫星、小行星、流星体，星际物质