Astrophysics Flashcards

1
Q

light year

A

Distance travelled by light in 1 yr

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2
Q

Luminosity

A

total amount of energy emitted by the star per second

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3
Q

apparent brightness

A

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

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4
Q

black-body radiation

A

a black body is a perfect emitter of energy

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5
Q

Stephan Boltzmann law

A

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

Power per unit area= σT^4

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6
Q

spectrum classification

A

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

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7
Q

HR diagram

A

luminosity by temperature

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8
Q

white dwarf (characteristics)

A

small and hot

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9
Q

main sequence (characteristics)

A

large and hot to small and cold (prop.)

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10
Q

Giants (characteristics)

A

large and cool

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11
Q

Supergiants (characteristics)

A

vary large and cool

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12
Q

Stellar spectra

A

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

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13
Q

Doppler effect

A

damage in perceived frequency with relative frequency

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14
Q

Variable stars

A
Cepheid variables
Binary stars (Visual/eclipsing/spectroscopic)
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15
Q

parsec

A

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

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16
Q

stellar parallax

A

can be extended to 1000pc

17
Q

spectroscopic parallax

A

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

18
Q

absolute magnitude

A

magnitude of a star from 10pc (distance)

19
Q

apparent magnitude

A

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

20
Q

Cepheid variables

A

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
Q

newtons model of the universe

A

infinitely large and old

static

22
Q

olber’s paradox

A

if infinitely large, sky infinitely bright

red shifts- distant stars receding- universe expanding

23
Q

big bang model

A

big bang originated across all space at same time

24
Q

hubble’s law

A

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