1、备课资料Further readingStarsStars vary greatly in size, mass and temperature. Some are 450 times smaller than the sun while some are over 1000 times bigger than the sun. Masses range from about a twentieth to over 50 solar masses. Due to various temperatures, the colors of stars are different: the hotte
2、st stars are blue and the coolest are red.The southern sky is the center of the Milky Way, with a large amount of stars. As a result, the Milky Way appears brighter in the southern sky than in the northern sky. When you look at the sky, youll find the moon seems much larger than most stars. That is
3、because the stars are much more distant. The nearest star outside the Solar System is more than 50 000 times further away than the planet Jupiter.Stars make fixed patterns in the sky called constellations. However, the constellations are not groupings of stars, since the distances among stars in a c
4、onstellation may vary greatly. The shapes of constellations may change over many thousands of years due to the relative motions of stars. The movement of the constellations across the sky is due to the Earths motion in space. The daily rotation of the Earth causes the constellations to move across t
5、he sky from east to west, and the orbit of the Earth around the sun causes different areas of sky to be visible in different seasons. The visibility of areas of sky also depends on the places of the observer. For example, stars near the celestial equator may be seen from either hemisphere at some ti
6、me during the year, but stars close to the celestial poles can only be seen from one hemisphere.A huge mass of stars forms a galaxy. The smallest galaxy contains about one million stars, while the largest contains 300 billion stars. It is impossible for one to see the Milky Way Galaxy clearly with the naked eye. However, you can get a clearer picture with the help of astronomical telescope.
