An astronomer would most likely use the Doppler effect to measure the color of a star.

measure the parallax of a star.
c

measure the brightness of a star.

measure the shift in the emission spectrum of a star.

i'd say that the moon rock is about 2.2 billion years old.

what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.