m, apparent magnitude – how bright an object (star) appears to be
from Earth
M, ABSOLUTE magnitude – how bright a star/galaxy appears to be
from a distance of 10 parsecs
Distance measured in parsecs !!!
Hipparchus’ scale
Jump of 1 magnitude = x 2.5
Luminosity = total power EMITTED from star (in Watts)
= total energy EMITTED per second (P = E/t)
Intensity, I = total power RECEIVED at distance d. (in Watts/m2)
.
One astronomical unit (AU) is defined as the mean
distance between the Earth and the Sun.
.
One lightyear (ly) is defined as the distance that
electromagnetic waves travel in a vacuum in one year