Measuring Distance through Stellar Parallax

a method of triangulation for measuring distance to nearby stars
arcsec = 1/60 of arcmin, which is 1/60 of a degree of arc
if A = 1 AU, B (distance) is inversely proportional to angle p if the angle in radian is much smaller than 1.

parsec (pc) = distance corresponding to a parallax of 1 arcsec. 1 pc is about 3.3 light year or 3 x 10¹³ km.
Quiz 12a

Inverse Square Law and Luminosity

luminosity = total amount of power radiated into space per unit time
inverse square law = a relationship between luminosity, distance, and apparent brightness
"a light appears brighter as you approach the light"

the same number of photons leave the star
a spherical shell surrounding the star increases its area as distance squared
apparent brightness (number of photons per unit area) decreases as distance squared

a logarithmic system of describing stellar brightness
1 magnitude = (100)^1/5 = a factor of 2.512
the brightest stars are 1st magnitude, the next brightest stars are 2nd magnitude, and so on. A larger magnitude means fainter -- see an example below of Ursa Major
apparent magnitude: how bright different stars appear in the sky
absolute magnitude: a measure of stellar luminosity (a star's apparent magnitude if it were at a distance of 10 parsecs away)

seeing how bright the light is, you can figure out how far the house is
if you know L, you can measure B and determine distance, d
"standard candle" = any object of known luminosity that can be used to determine distances (e.g. stars of known mass and luminosity)