11B.3 Distances to the stars

Question 1

what is a light year

Answer 1

the distance that light can travel in one year, in a vacuum, which is about 10^16

Question 2

what is astronomical unit AU

Answer 2

a distance unit, equal to the radius of the earths orbit around the sun 1 AU = 1.5 x 10^11

Question 3

what is the trigonometric parallax

Answer 3

a method for measuring to distance to relatively close stars. it works by comparing their measured angle in the sky at six months intervals, and using these measurements to calculate the distance using trigonometry

Question 4

how can we measure the angel between the star and the earth

Answer 4

by measuring the star against a background of distance star across a sixth month interval, where the earth would be in the same position on the other side

Question 5

what is parallax angle

Answer 5

the difference in angular observation of given star, for use in the trigonometric parallax method to measure distance of the star

Question 6

at small angles tan angle will equal

Answer 6

angle

Question 7

what is parsec

Answer 7

the distance the star must be from the sun in order for the parallax angle to be 1 arcsecond

1 pc = 3.09 x 10^16

Question 8

if angle is measured in arcsecond what is the distance of the star in parsecs

Answer 8

d = 1/angle

Question 9

how much is one arcsecond in degrees

Answer 9

3600 since 1 degree can be split to 60 minutes and 1 minute can be split to 60 seconds

Question 10

what is the equation of intensity of a star

Answer 10

I = L/A = L/4pir^2

Question 11

what does the intensity equation tell us

Answer 11

the energy emitted by star will spread out in all directions over a surface area of an increasing sphere following the square inverse laws

Question 12

what are standard candles

Answer 12

starts with properties such that their luminosity can be determined from measurements other than brightness

Question 13

what are variable stars

Answer 13

stars in which their brightness change every repeating cycle

Question 14

in variable stars what is the rs between the time period of oscillation brightness and luminosity

Answer 14

the time period for the oscillations brightness was constant and directly proportional to the luminosity of each star

Question 15

what is the rs between time period of oscillations and brightness

Answer 15

the longer the time the brighter the star

Question 16

what are the two variable stars that allow us to measure the distance of stars

Answer 16

1. RR lyrae variable stars
2. cepheid variable stars

Question 17

how can we use variable starts to measure the stars distance

Answer 17

we take the rs between the time period of oscillations and luminosity to find luminosity and then use the expression for brightness

Question 18

how can we measure the luminosity of a star using its specturm

Answer 18

form the spectrum we can find its peak wavelength then using Wiens law its temperature, and also the width so the spectral lines which tell us if its in the main sequence or not and if it is we can locate it on the Hertzsprung-Russel diagram and find luminosity on the y-axis. this is least reliable