How did ancient astronomers classify stars?
on the basis of their absolute magnitude
on the basis of their apparent magnitude
O on the basis of brightness
on the basis of their distance from Earth

Two solids are mixed in a flask and stirred. after a few minutes, the flask becomes cold. which of the following best describes this reaction? a. an exothermic reaction b. a combustion reaction c. an endothermic reaction d. a decomposition reaction