Question

To know certain properties of a star, you must first determine the star’s distance. For other properties, knowledge of distance is not necessary. Explain why an astronomer does
 or does not need to know a star’s distance to determine each of the following properties: size, mass, temperature, color, spectral type, and chemical composition? In each case, state your reason(s). 


Answer 1

Screen 1 of 1 View Options, X Close Color does not change over a distance, except because of redshift. Redshift can be detected by the shift of spectral lines and adjusted for. So color does not require knowledge of distance Temperature is directly related for color, so also falls into that category. Chemical composition is analyzed based on the strength of spectral lines, which aren't altered by distance. Position is altered by redshift, but the pattem remains identifiable and the strength is what is important to composition, not position. Spectral type depends on color and the same spectral lines that relate to composition The remaining two properties require distance to determine Mass correlates with absolute luminosity, but absolute luminosity cannot be measured. Apparent magnitude can be measured, and with knowledge of distance absolute luminosity can be inferred, and then mass. Size correlates with temperature and absolute luminosity. Temperature can be measured but again, absolute luminosity cannot be, directly ENG 07:28 הז US 24-03-2017