Distances and Magnitude

Question 1

What’s it the luminosity of a star?

Answer 1

The total energy it emits in the form of electromagnetic radiation per second
Measured in watts
It’s the power output of a star

Question 2

What is the intensity of an object that we observe?

Answer 2

Power received from it per unit area at earth

Question 3

What is the effective brightness of an object?

Answer 3

Its intensity

Question 4

What is apparent magnitude?

Answer 4

How bright the object appears from earth

Question 5

What does the brightness of a star in the night sky depend on? (ignoring weather and light pollution)

Answer 5

Its luminosity and its distance (closer = brighter)

Question 6

What is the scale of apparent magnitude?

Answer 6

1 = brightest 
6 = dimest

Question 7

A magnitude 1 star has an intensity how many times greater than a magnitude 6 star?

Answer 7

100 times

Question 8

What’s the equation for calculating brightness ratio between 2 stars?

Answer 8

I2 / I1 = 2.51^m1-m2

Difference of 1 on the apparent magnitude scale is 100^1/5 = 2.51

Question 9

Brightness of sun?

Answer 9

m = -26.7

Question 10

Dimmest objects Hubble telescope can see on scale?

Answer 10

m = 30

Question 11

What planet, with m=0, is the apparent magnitude scale tied to?

Answer 11

Vega

Question 12

What is a parallax?

Answer 12

The apparent change in position of an object as the observer moves position.

Question 13

Parallax is measured in?

Answer 13

An angle

Question 14

How is the distance to nearby stars calculated using parallax?

Answer 14

Question 15

What is the distance between each end of earths orbit

Answer 15

6 months

Question 16

What is the angle of parallax?

Answer 16

When you view a star from each end of earths orbit (6 months apart), the angle in-between the earths positions
(6 months apart) and the star, divided by 2 is the angle of parallax. Its also the angle between the sun and the earth when the angle is at the star.

Question 17

What happens to parallax angle when the star is closer

Answer 17

Bigger angle of parallax

Question 18

If you know the angle of parallax what do you do to find the distance between the earth and the star?

Answer 18

Trigonometry:

Question 19

How do you find the distance between the earth and star if the angle is small?

Answer 19

Presume tan(x) = x

Question 20

1 arc second = X degrees?

Answer 20

X = 1/3600

Question 21

1 degree = X arcseconds?

Answer 21

X = 3600

Question 22

How many parsecs away is a star if it’s parallax angle is 1 arcsecond

Answer 22

1 parsec

Question 23

Absolute magnitude is and isn’t based on what?

Answer 23

Only luminosity (or power output), not the distance.

Question 24

What is absolute magnitude defined as?

Answer 24

what its apparent magnitude would be if it was 10 parsecs away

Question 25

What is M, m and d in the brightness equation

Answer 25

Question 26

Why can't parallax be used to measure the distance to most stars?

Answer 26

They are too far away

Question 27

What is a standard candle? Whats an example?

Answer 27

An object that you can calculate the luminosity directly e.g. type 1a supernova

Question 28

All type 1a supernovae have the same what?

Answer 28

Same peak in absolute magnitude = -19.3

Question 29

What is the rearranged brightness equation?

Answer 29

Question 30

1 AU is defined as what?

Answer 30

The mean distance from the sun to the earth

Question 31

What is a light year?

Answer 31

The distance that electromagnetic waves can travel in one year, in a vacuum

Question 32

If we see light from a star 10 light years away, we are seeing it as if it were X years ago/ahead

Answer 32

Seeing it as if it were 10 years ago. | Further away an object is further back in time we see it.

Question 33

How do you work out half the angle subtended by the object at the eye, knowing the distance away and radius of the object?

Answer 33

Question 34

When is parallax used?

Answer 34

When the object is nearby

Question 35

When is the angle subtended used? Why is it unlikely that you know it?

Answer 35

If we know the objects size. It's unlikely we have the size if we don't know the distance

Question 36

Why is using other methods like red-shift, standard candles and quasars useful for measuring distance?

Answer 36

Several ways can make it more precise

Question 37

hi

Answer 37

hello