Star A is hotter. Both are at the same temperature. There is not enough information provided to give an answer. The 21-cm line of neutral hydrogen is produced by a. collisions between heavy ions and free electrons. Dust in the interstellar medium will cause a star to appear from our viewpoint on Earth to be a. brighter and cooler than it really is.
Brown dwarfs are a. stars surrounded by huge circumstellar disks.
200km, water molecule. 2000km, interstellar cloud. 20000km, main sequence star. The two classes of spiral galaxies are a. elliptical and barred. One particular feature of the solar corona is a. its variation with time over periods of a few minutes.