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physics > Astrophysics > Flashcards

Astrophysics Flashcards

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1
Q

What is apparent magnitude?

A

m - brightness measured by an observer at a specific distance

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2
Q

What is absolute magnitude?

A

M - it is defined as what its apparent magnitude would be if it were 10 parsecs away from earth
it is based on the power output of an object, it does not depend on distance.

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3
Q

What are the units for luminosity

A

watts

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4
Q

what is the formula for luminosity

A

L = 4pie x d^2 x b where d is distance from, and b is intensity

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5
Q

how do we draw convex lens’s

A

arrow pointing outwards

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6
Q

how do we draw concave lens’s

A

arrows pointing inwards

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7
Q

what is the principle focus

A

where the light rays meet and cross

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8
Q

what is the principle axis

A

horizontal to the lens

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9
Q

what is the focus length

A

distance from lens to focal point (f)

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10
Q

what is magnification

A

(M) a ratio of size to actual size

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11
Q

a shorter wavelength of light has a shorter focal length, which colour has the shortest focal length.

A

blue has the shortest focal length

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12
Q

if the resolving power is high

A

the lower minimum angular resolution

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13
Q

two light sources can only be distinguished when?

A

their airy discs from one source is at least as far as the first minimum of the other

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14
Q

collecting power is proportional to what?

A

dish diameter squared or area

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15
Q

how do you remember star classification

A

Oh Boy, An F Grade Kills Me.

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16
Q

what is the colour of an O star

A

blue

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17
Q

what is the colour of an M star

A

orange/ red

18
Q

what are the temperature ranges for an O star

A

greater than 30,000 k

19
Q

what are the temperature ranges for an B star

A

10,000 to 30,000 k

20
Q

what are the temperature ranges for an A star

A

7,500 to 10,000 k

21
Q

what are the temperature ranges for an F star

A

6,000 to 7,500 k

22
Q

what are the temperature ranges for an G star

A

5,200 to 6,000 k

23
Q

what are the temperature ranges for an K star

A

3,700 to 5,200 k

24
Q

what are the temperature ranges for an M star

A

2,400 to 3,700 k

25
Q

which class of star has strong hydrogen lines?

A

A / B

26
Q

how do you plot a black body radiation curve

A

use wines law to find the max wavelength then plot a skewed bell curve

27
Q

what special lines appear in a O star?

A

ionised helium

28
Q

what special lines appear in a B star?

A

helium, some hydrogen

29
Q

what special lines appear in a A star?

A

strong hydrogen, some ionised metals

30
Q

what special lines appear in a F star?

A

hydrogen, ionised calcium and iron

31
Q

what special lines appear in a G star?

A

neutral and ionised metals, especially calcium

32
Q

what special lines appear in a K star?

A

neutral metals, sodium

33
Q

what special lines appear in a M star?

A

strong titanium oxide, very strong sodium

34
Q

what must you refer to when comparing size of stars

A

spectral class and thus temperature

35
Q

if a star has a greater power output what else must be true?

A

it must have a larger surface area

36
Q

how can we work out the temperature of a star knowing its max wavelength of a black body radiation curve

A

wiens law

37
Q

explain what is meant by a parsec

A

distance at which the radius of the earths orbit subtends at an angle of one arc second

38
Q

if a star has the same brightness/power as another star how to we tell which is larger

A

the hotter star will be larger due to stefan’s law

39
Q

why do classes A and B have the most prominent hydrogen balmer lines/

A

their temperatures are between 10 and 30 000k which is hot enough to have hydrogen in n=2 state

40
Q

describe the radial velocity method

A

the star causes a periodic doppler shift of light received due to the star orbiting a common centre of mass. red shift could then increase and decrease periodically showing there is an exoplanet orbiting

41
Q

how do we use Hubbles constant to find the age of the universe?

A

divide by 3.08x10^19 for k ms-1 Mpc-1 then 1/ans

physics (12 decks)

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