Which of the following properties do astronomers look at in order to classify stars? A. color B. size C. brightness D. all of these

The answer was B. Brightness because They are classified by distance, brightness (magnitude) or spectrum. There are five main types of star spectrums, called A, F, G, K, M. White A type stars are the hottest (e. g. Sirius, Rigel) while red M type ones are the least hot (Betelgeuse).