Class Notes (1,100,000)
CA (630,000)
UTSG (50,000)
AST (700)
AST201H1 (200)
Lecture

luminosity, parallax, stars, spectral class


Department
Astronomy & Astrophysics
Course Code
AST201H1
Professor
Stefan Mochnacki

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Lecture 8
-luminosity: how bright- how much light the star is emitting (all)
-there are a few things u can tell by just looking at stars
colour: blackbodies (thermal radiation) temperatures, Doppler shift (moving
towards, away)
if a star is blue, we know for sure it is: we cant say for sure because it could be
hotter or its moving rapidly towards us
Parallax
-there are a great variety of techniques used to determine the distances to
stars for nearby stars, we use parallax
-a bigger jump distance difference- closer star, a smaller jump- further star
STARS- continued
-earth receives only a small fraction of the suns light
this small fraction of light that we receive is called apparent brightness or
apparent magnitude
-the amount of light received from a star falls with the square of our distance
from it
this is called: inverse square law of light
apparent brightness = luminosity/ 4(pi)(d^2)
we measure the apparent brightness
less light received, the further away the planet from the sun, more light received,
the closer the planet from the sun
-tells us how much fusion is going on in the star- brightness
-we find out the chemical composition or what the star is made of through
absorption spectrum
-Annie Jump Cannon- realized that you could get rid of most of the spectral
categories keeping only A,B,F,G,K,M and O formed a pattern
Oh, Be A Fine Girl, Kiss Me
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