AST201H1 Lecture 9: Lecture#9 Feb.3rd

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST201H1
• Professor: Michael Reid

Document Summary

Luminosity: the amount of energy an object emits per unit time: luminosity of a light bulb= 100 watts, luminosity of the sun = 4 x 1026 w = one solar luminosity or 1 l . Luminosity tells how bright something is intrinsically. Apparent brightness is how bright something looks to us on earth. *sometimes we use absolute magnitude and apparent magnitude instead of luminosity and apparent brightness, but you can ignore that. Even the ancient greeks knew how, although they couldn"t actually perform the required measurements. We can measure the distances to nearby stars using parallax which requires knowing the earth-sun distance (au) first from the radar. Parallax is an apparent motion, not an actual motion. Stellar parallax is caused by earth"s orbit around the sun: the positon of nearby star appears to shift against the background of more distant stars. The more distant a star, the smaller its parallax angle.