哈工大天文学概论——恒星结构及能源.pptVIP

Sample Star Distribution 质量－半径关系(mass-radius relation)： R ~ M 0.5-1 质光关系(mass-luminosity relation)： L ~ M 2-4 赫罗图H-R Diagram 1913年，美国天文学家Henry Norris Russell (罗素)把太阳近邻恒星的光度和光谱型绘制在一张图上。 光度 – 光谱型分布图 1911年，丹麦天文学家Ejnar Hertzsprung(赫兹普隆)把同一个星团的每一颗恒星的亮度对色指数创制成一张图。 恒星在赫罗图上的分布特征 主序星 Conclusions from the H-R Diagram Conclusions from the Hertzsprung-Russell Diagram Stars can be classified into different groups. Most stars lie in a band stretching(伸展) from very red low-luminosity stars to blue stars that are very, very luminous. Very few stars are red and luminous. Even fewer stars are ‘white’ and have a low luminosity. Why is there such an order ? 100颗最亮的恒星在赫罗图上的分布 太阳附近5pc范围内的恒星在赫罗图上的分布 Basic Sun Data Distance to Earth Mean Distance : 1 AU = 149,598,000 km (light travel time to Earth = 8.32 min) Maximum : 152,000,000 km Minimum : 147,000,000 km Mean angular diameter : 32 arcmin Radius : 696,000 km = 109 Earth radii Mass : 1.9891 x 1030 kg = 3.33 x 105 Earth Masses Basic Sun Data Composition (by mass) 74% Hydrogen, 25% Helium, 1% other elements Composition (by number of atoms) 92.1% Hydrogen, 7.8% Helium, 0.1% other elements Mean Density : 1.4 g cm-3 Mean Temperatures Surface 5800 K, Centre 15.5 Million K (!) Total Luminosity : 3.86 x 1026 W (1 sec ? enough energy for 1 million years for humankind) How old is the Sun ? Really problematic : Sun does not come with a time-stamp, shows no wrinkles etc… Start with Earth Solar System Date geological formations, rocks(地质层组) Various geochronometrical methods using radioactive decay properties ? 4.2 billion years Find oldest meteorites(陨星) ? 4.5-4.7 billion years Conclusion : Sun at least that old ! Models of the Sun Solar surface temperature ~ 5800 K Temperature required for fusion ~ 10 million K Fusion can only occur at core of the Sun ! Can we understand and describe the conditions inside the Sun ? Use theoretical models ! Start with well-known principles and laws of physics Models of the