Astrophysics

Question 1

light year

Answer 1

Distance travelled by light in 1 yr

Question 2

Luminosity

Answer 2

total amount of energy emitted by the star per second

Question 3

apparent brightness

Answer 3

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

Question 4

black-body radiation

Answer 4

a black body is a perfect emitter of energy

Question 5

Stephan Boltzmann law

Answer 5

power per unit area prop. to the 4th power of temperature

Power per unit area= σT^4

Question 6

spectrum classification

Answer 6

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

Question 7

HR diagram

Answer 7

luminosity by temperature

Question 8

white dwarf (characteristics)

Answer 8

small and hot

Question 9

main sequence (characteristics)

Answer 9

large and hot to small and cold (prop.)

Question 10

Giants (characteristics)

Answer 10

large and cool

Question 11

Supergiants (characteristics)

Answer 11

vary large and cool

Question 12

Stellar spectra

Answer 12

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

Question 13

Doppler effect

Answer 13

damage in perceived frequency with relative frequency

Question 14

Variable stars

Answer 14

Cepheid variables
Binary stars (Visual/eclipsing/spectroscopic)

Question 15

parsec

Answer 15

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

Question 16

stellar parallax

Answer 16

can be extended to 1000pc

Question 17

spectroscopic parallax

Answer 17

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

Question 18

absolute magnitude

Answer 18

magnitude of a star from 10pc (distance)

Question 19

apparent magnitude

Answer 19

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

Question 20

Cepheid variables

Answer 20

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

Question 21

newtons model of the universe

Answer 21

infinitely large and old

static

Question 22

olber’s paradox

Answer 22

if infinitely large, sky infinitely bright

red shifts- distant stars receding- universe expanding

Question 23

big bang model

Answer 23

big bang originated across all space at same time

Question 24

hubble’s law

Answer 24

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

Question 25

age of universe

Answer 25

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

Question 26

Cosmic microwave background

Answer 26

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)

Question 27

open universe

Answer 27

expands forever

less than critical density

Question 28

critical universe

Answer 28

expands, but rate eventually decreases to 0

at critical density

Question 29

closed universe

Answer 29

one point stops expanding and starts contracting

greater than critical density

Question 30

critical density

Answer 30

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

Question 31

difficulty in estimating density of space

Answer 31

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

Question 32

constellation

Answer 32

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

Question 33

bx/by

Answer 33

=2.512^my-mx

Question 34

Lx/Ly

Answer 34

=2.512^My-Mx