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AQA A-Level Astrophysics > Distances and Magnitude > Flashcards

Distances and Magnitude Flashcards

1
Q

What’s it the luminosity of a star?

A

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

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2
Q

What is the intensity of an object that we observe?

A

Power received from it per unit area at earth

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3
Q

What is the effective brightness of an object?

A

Its intensity

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4
Q

What is apparent magnitude?

A

How bright the object appears from earth

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5
Q

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

A

Its luminosity and its distance (closer = brighter)

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6
Q

What is the scale of apparent magnitude?

A 
1 = brightest 
6 = dimest
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7
Q

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

A

100 times

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8
Q

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

A

I2 / I1 = 2.51^m1-m2

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

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9
Q

Brightness of sun?

A

m = -26.7

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10
Q

Dimmest objects Hubble telescope can see on scale?

A

m = 30

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11
Q

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

A

Vega

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12
Q

What is a parallax?

A

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

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13
Q

Parallax is measured in?

A

An angle

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14
Q

How is the distance to nearby stars calculated using parallax?

A
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15
Q

What is the distance between each end of earths orbit

A

6 months

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16
Q

What is the angle of parallax?

A

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.

17
Q

What happens to parallax angle when the star is closer

A

Bigger angle of parallax

18
Q

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

A

Trigonometry:

19
Q

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

A

Presume tan(x) = x

20
Q

1 arc second = X degrees?

A

X = 1/3600

21
Q

1 degree = X arcseconds?

A

X = 3600

22
Q

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

A

1 parsec

23
Q

Absolute magnitude is and isn’t based on what?

A

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

24
Q

What is absolute magnitude defined as?

A

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

25
Q

What is M, m and d in the brightness equation

A
26
Q

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

A

They are too far away

27
Q

What is a standard candle? Whats an example?

A

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

28
Q

All type 1a supernovae have the same what?

A

Same peak in absolute magnitude = -19.3

29
Q

What is the rearranged brightness equation?

A
30
Q

1 AU is defined as what?

A

The mean distance from the sun to the earth

31
Q

What is a light year?

A

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

32
Q

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

A

Seeing it as if it were 10 years ago.

Further away an object is further back in time we see it.

33
Q

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

A
34
Q

When is parallax used?

A

When the object is nearby

35
Q

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

A

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

36
Q

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

A

Several ways can make it more precise

37
Q

hi

A

hello

AQA A-Level Astrophysics (11 decks)

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