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Flashcards in Astrophysics Deck (34):
1

light year

Distance travelled by light in 1 yr

2

Luminosity

total amount of energy emitted by the star per second

3

apparent brightness

the amount of energy received from the star per unit area per second

4

black-body radiation

a black body is a perfect emitter of energy

5

Stephan Boltzmann law

power per unit area prop. to the 4th power of temperature
Power per unit area= σT^4

6

spectrum classification

Oh Be A Fine Girl Kiss Me (classification)
But Will You Run (colour)
50k(28)10k(7.4)6k (5) 2k (Temp in k=1000)a

7

HR diagram

luminosity by temperature

8

white dwarf (characteristics)

small and hot

9

main sequence (characteristics)

large and hot to small and cold (prop.)

10

Giants (characteristics)

large and cool

11

Supergiants (characteristics)

vary large and cool

12

Stellar spectra

the broad peaks can find surface temperature using : λmax=2.9*10^3
dark lines - gases present (absorption)
affected by Doppler effect

13

Doppler effect

damage in perceived frequency with relative frequency

14

Variable stars

Cepheid variables
Binary stars (Visual/eclipsing/spectroscopic)

15

parsec

the distance at which the angle subtended by the radius of Earth's orbit is 1 arc-second
d(parsec)=1/p(arc-second)

16

stellar parallax

can be extended to 1000pc

17

spectroscopic parallax

only needs spectrum and apparent brightness
d=(L/4πb)
spectrum-peak wavelength-temperature-position HR-luminosity-distance

18

absolute magnitude

magnitude of a star from 10pc (distance)

19

apparent magnitude

brightness of a star as appears from Earth in a relative classification system on log scale

20

Cepheid variables

variation of luminosity- because way radiation emitted interact with He in the outer layers
(as He heats, absorption increases and expands, cools as)
time period-luminosity-distance

21

newtons model of the universe

infinitely large and old
static

22

olber's paradox

if infinitely large, sky infinitely bright
red shifts- distant stars receding- universe expanding

23

big bang model

big bang originated across all space at same time

24

hubble's law

distance between receding galaxies prop to recession velocity
Ho= recession velocity/separation distance

25

age of universe

time elapsed=distance travelled/speed=separation distance/recession velocity=1/Ho (10^18)

26

Cosmic microwave background

electromagnetic radiation that fills the universe & received from all directions
big bang-large energy produced at start by fusion, - expansion=cooling
solves olber's paradox (finite time- some too far away and red shifted to reach earth)

27

open universe

expands forever
less than critical density

28

critical universe

expands, but rate eventually decreases to 0
at critical density

29

closed universe

one point stops expanding and starts contracting
greater than critical density

30

critical density

if actual density of the universe≥ critical density =closed universe
vice versa for open universe

31

difficulty in estimating density of space

not uniform around universe
difficult to measure volume accurately (red shifted light)
not all matter detected

32

constellation

a pattern of stars in a sky, but not necessarily close to each other or gravitationally bound

33

bx/by

=2.512^my-mx

34

Lx/Ly

=2.512^My-Mx