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