What makes something a compound microscope

A compound microscope is an upright microscope that uses two sets of lenses (a compound lens system) to obtain higher magnification than a stereo microscope. A compound microscope provides a two-dimensional image, while a stereo microscope provides a three-dimensional image.  

Explanation:

blue stars have the highest surface temp

stellar distances are usually expressed in light-years

the measure of a star's brightness is called magnitude

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