Star Characteristics:
How far (d in parsecs)?
Distance to nearby star determined from stellar parallax, p,
which is ½ the maximum angular difference in
position:
d (in parsecs) = 1/p (p in arc
seconds)
1 parsec is the distance at which the parallax of a
star is 1 arcsec.
Parallax method works for stars closer than about 100
parsecs.
(1 parsec = 3.26 LY.)
How bright (L in watts)? Luminosity at
the source is determined
from apparent brightness and distance (d).
Apparent magnitude (old way). We can see about 1,000 stars in
Northern Hemisphere with naked eye. Hipparchus rated them from
1 to 6. A '1' is
2.52 x brighter than a '2', etc. Range
in brightness
from the sun at '-26' magnitude to the faintest objects
seen at about
'26' magnitude.
Flux (new
'apparent brightness'):
b (watts/m2) = L/4πd2 = Power/unit
area of sphere.
From d, the distance, we get L, the luminosity (watts
of source).