it is good to know because once you hit high school your life will change. its good to think a bout because once your 16 you can start a short term job. but as soon as your 18 your gonna want to hang with people so you would need a career so you can start to earn money at a young age so you can see your friends, buy a house, buy a car , etc..
From the brightness of the light of course. If the brightness is increasing it means the the light source is approaching and if the brightness is decreasing it means the light source is leaving.
