Astrophysics - classification Flashcards
Define Luminosity, L
The energy an object radiates per second, measured in watts
Define Brightness, b
The intensity of the radiation an object radiates, measured in watts per metre squared
What is the equation for brightness?
L / 4πr²
What does the hipparchus scale measure and what is its original range?
A scale of apparent magnitude, m, with the brightest stars viewed by the naked eye from earth at 1.0, and dimmest 6.0
How was the hipparchus scale extended?
Even brighter stars were extended into negative values (the MORE NEGATIVE the BRIGHTER) and dimmer starts were extended too values larger than 6 (the LARGER the DIMMER)
What is Pogson’s law?
m₂ - m₁ = -2.5 log₁₀(b₂/b₁)
NOT ON DATA SHEET
What is 1 astronomical unit?
The earth too sun distance
Define the parsec
The distance at which the observed parallax angle is 1’’ arcsecond
Define a light year
The amount of distance a photon travels in one year travelling at the speed of light
Define absolute magnitude
The magnitude, M, a star would have if places 10 parsecs from earth
Define apparent magnitude
The magnitude, m, of a star as viewed from earth
Which is apparent magnitude and absolute magnitude, M or m?
M - absolute m - apparent
What is the distance modulus?
m - M
What is a standard candle?
Object with a known absolute magnitude
What is a cepheid variable, how does it help us discover standard candles?
A star whose apparent magnitude changes periodically. Said period strongly correlates with the stars average absolute magnitude.
What properties of a star are effected by its temperature?
Colour, Luminosity and spectral lines
How does Wein’s law explain the relationship between a stars temperature and its colour?
As its temperature increases, it must emit radiation of a shorter maximum wavelength -> blues.
As its temperature decreases, it must emit radiation of a larger maximum wavelength -> reds.
Numerically define Steffan’s law using the radius of the star (instead of A denoting area)
L = δ. 4πR². T⁴
What does Steffan’s law dictate as the brighter star when two stars have the same : Area, Temp
Same Area: The hotter star is brighter
Same Temp: The larger star is brighter
What does the presence of the spectral lines, the Balmer series, imply?
The star is hot enough too have a substantial amount of hydrogen in the n=2 state and, is a class O,B or A star.
Describe the appearance of the Balmer series
4 absorption lines in the visible spectrum
1 Red, 1 Green and 2 Blue-Purple
4 electron excitation lines from energy level n=2 too 3,4,5 and 6
What is the classification of stars in order from highest too lowest temperature?
O
B
A
F
G
K
M
What are the colours of the star classes?
O - Blue
B - Blue
A - Blue-White
F - White
G - Yellow
K - Orange
M - Red
