Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Yr 13 Physics 12 - Space > Distances to the Stars > Flashcards

Distances to the Stars Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

what is a light year and its value

A
  • it is the distance light can travel in one year

- which is 9.46x10^15 m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the definition of an astronomical unit (AU)

A

the radius of the earths orbit around the sun

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is the value of 1 AU

A

1.5x10^11 m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how does the trigonometric parallax illusion work with earth, the sun and other stars

A
  • as the earth moves around the sun
  • a relatively close star will appear to move across the background of more distant stars
  • but the star doesnt actually move significantly during the course of observation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how do you determine the the trigonometric parallax

A
  • measure the angle to a star

- observe how that angle changes as the position of the earth changes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what change in the position of the earth are we looking for and why

A
  • we are looking for the earth to be on the opposite side of its orbit relative to the sun
  • which would take 6 months
  • this means the distance the earth travelled (distance in a straight line) was 2 AU
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the large triangle that has been set up from the movement of earth around its orbit when observing another star

A
  • the two positions of the earth make one side of the triangle (2r)
  • while the distance between earth 6 months prior and the star makes one side
  • and the distance between earth now and the star makes the final side
  • the angle formed at the star is 2 theta
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what would distance d be in this case

A

the (horizontal) distance between the sun and the star

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

using the distance d, what new triangle could be made

A
  • a right angled triangle
  • the angle at the star is now just theta
  • the distance between the sun and star is d
  • the distance between the sun and earth is r
  • and the distance between the earth and star makes the hypotenuse
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

given that you usually only know r and d, what equation wold you use to calculate the parallax angle

A
  • r and d are the opposite and adjacent angles

- so tan0 = r / d

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

at small angles. what simplified equation could we use to calculate d and why

A
  • rearrange to d = r / tan0
  • giving d = r / 0
  • because tan0 approximates to just 0 at small angles
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the definition of a parsec (pc)

A
  • the distance a star must be from the sun

- in order for the right angle earth-star-sun to be 1 arcsecond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is the full name of a parsec

A

a parallax second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how do you convert arcseconds to angles

A

by dividing the arcseconds by 60x60 (3600)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how do you convert angles to arcminutes

A

by multiplying the angle by 60

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the symbol for 1 arcsecond and 1 arcminute

A
  • 1 arcsecond = 1”

- 1 arcminute = 1’

17
Q

if a parsec requires the angle at the star to be 1 arcsecond and it is defined to be the distance between the sun and the star, how would you work out the length of a parsec

A
  • earth to sun = 1AU (opposite)
  • angle at star = 1 arcsecond
  • sun to star = 1 parsec (adjacent)
  • therefore tan(1 arcsecond) = 1AU / 1 parsec
  • 1 parsec = 1AU / tan(1 arcsecond)
  • 1AU = 1.5x10^11 and 1 arcsecond = 1 / 3600
  • therefore 1 parsec = (1.5x10^11) / tan(1/3600)
18
Q

using that calculation, what is the value of 1 parsec

A

3.09x10^16 m

19
Q

what is the length of 1 parsec in light years

A

(3.09x10^16) / (9.46x10^15) = 3.27 light years

20
Q

if the angle measurement is in arcseconds (0), what equation could you use to calculate the distance d

A

d = 1 / theta (0)

21
Q

what is the equation for radiation flux

A

F = L / 4 pi d^2

22
Q

what are the variables in that equation

A
  • F = radiation flux / radiant energy intensity (Wm-2)
  • L = luminosity (W)
  • d = distance between star and observer (m)
23
Q

what is the difference between radiation flux and luminosity

A
  • luminosity is the total power output of a star from its surface
  • whereas radiation flux is the power from a star that reaches earth
24
Q

what are standard candles

A

Stars with properties which means their luminosity can be determined from measurements other than brightness

25
Q

how would you work out the distance these types of stars are away from us

A
  • work out their luminosity from earth (or just have it)
  • measure the radiation flux from earth
  • compare it with a standard candle with the same luminosity to work out how far away it is
26
Q

what did henrietta leavitt discover by observing many stars in the nearby magellanic clouds

A
  • that the brightness of some of the stars changed

- varying in a repeating cycle

27
Q

although the brightness of the stars varied, what was constant in her time-luminosity graph

A
  • the time period of the oscillations in brightness

- basically the time between the highest peaks were constant

28
Q

what is the brightness of the stars proportional to

A

the luminosity of the star

29
Q

why does this alternation in brightness even occur in the first place

A
  • these stars have left the main sequence stage
  • but hey havent exhausted all of their fuel
  • the unbalancing between its gravity and thermal expansion cause the star to repeatedly expand and contract
  • causing their surface areas as therefore luminosity (and therefore brightness) to vary
30
Q

what did a star having a longer period for oscillation imply about it

A

it was brighter than others

31
Q

after you have found a cepheid star, how do you use it to work out the distance between earth and it

A
  • measure the time period for that star (between times of peak brightness)
  • find the stars luminosity using leavitts time-luminosity data
  • measure the radiation flux from the star on earth
  • calculate d using F = L / 4 pi d^2
  • its literally the same thing with the standard candles but this is more accurate
32
Q

what is the simplest way of determining the luminosity of a star

A

by looking at its spectrum

33
Q

how does looking at its spectrum work

A
  • the peak wavelength gives the temp from weins law
  • the width of the spectral lines can determine whether its a M.S. star
  • if it is you find its place on the M.S. section on the luminosity-temp graph
  • thereby giving you luminosity
34
Q

what is the definition of a parallax angle

A
  • the difference in angular observation of a given star

- for use in the trigonometric parallax method of measuring the distance to a star

35
Q

what is the definition of the trigonometric parallax

A

a method for measuring the distance to relatively close stars

Yr 13 Physics 12 - Space (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions