PCS 181 Lecture Notes - Lecture 8: Apparent Magnitude, Absolute Magnitude, Hypotenuse

• School: Ryerson University
• Department: Physics
• Course: PCS 181
• Professor: Margaret Buckby

Document Summary

Recall the distance units used in astronomy. Light-year = 1ly = distance that light travels in one year = 1ly=9. 5 x 1015 m. Parsec = pc = 1 pc = 3. 26 ly. Astronomical unit = au = average distance between the earth and sun. Sin 0 = opposite = 1 = 0 (for small angles). D = 1, if 0 is in seconds of are ( ), then d is in parsecs (pc). D = 3. 26, if we multiply by 3. 26, then d is in light-years (ly). This method is good for stars at d < ~50 pc (163 ly). Hipparchus (hippocras) of greece (2nd century b. c. ) divided the visible stars into 6 groups. M = 1 (brightest star in greek sky). M = 1 is 2. 5 times as bright as m = 2. M = 2 is 2. 5 times as bright as m = 3 etc. Star = starlight = photocell = current = meter = computer.