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Astronomy GCSE > Physical Properties of Stars > Flashcards

Physical Properties of Stars Flashcards

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1
Q

What’s the difference between a constellation and a cluster of stars?

A

Stars in a constellation are not physically related, while stars in a cluster are associated gravitationally.

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2
Q

What’s the difference between an optical double star and a binary star?

A

Optical double stars only appear in line with each other and the observer when viewed with inadequate magnification. They may be separated great distances from each other. Stars in a binary system are gravitationally related and orbit their common centre of mass.

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3
Q

Give two examples of stars in a binary system.

A 
Castor from Gemini.
Algol B(Per).
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4
Q

1 magnitude scale downwards=

A

2.5x brighter

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5
Q

Who came up with the first proposed system of magnitude?

A

Ptolemy, who suggested that each scale was 2 times brighter than the next.

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6
Q

When was the current magnitude system devised?

A

1856.

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7
Q

What is m=1 100 x brighter than?

A

m=6

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8
Q

What is the highest magnitude star that is visible to the naked eye?

A

m=6

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9
Q

What is the constant star today, and what is their magnitude?

A

Vega, at m=0

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10
Q

What was previously the constant star, and what was its magnitude?

A

Polaris, at m=2

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11
Q

Why is Polaris no longer used as the constant star?

A

Its magnitude was later found to be variable.

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12
Q

What is the brightest star in the sky, and what is its magnitude?

A

Sirius, -1.5

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13
Q

What is Vega?

A

The 4th brightest star in the sky.

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14
Q

List 4 factors influencing apparent magnitude.

A 
Distance to star.
Original luminosity (size and temperature).
Amount of absorbing atmosphere light passes through.
Amount of interstellar dust and gas.
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15
Q

What two factors influence absolute magnitude?

A

Size

Temperature

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16
Q

What is 1 parsec in light years?

A

3.3 light years

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17
Q

What is 1 parsec in AU?

A

200,000AU

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18
Q

What is 1 parsec in km?

A

3.1 x 10^13km.

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19
Q

What is the speed of light?

A

3 x 10^8 km/s

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20
Q

Why are stars difficult to locate?

A

Cannot use space probes.
Radar would take years to return.
Returned signal would be so weak it would be indistinguishable from background noise
Stars are spheres of gas and do not have hard reflecting surfaces.

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21
Q

What is 1 degree in minutes of arc?

A

60 minutes of arc

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22
Q

What is 1 minute of arc in seconds of arc?

A

60 seconds of arc

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23
Q

What is 1 degree in arcseconds?

A

1/3600 arcseconds

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24
Q

Define heliocentric parallax.

A

The apparent motion of near and more distant objects in respect to each other caused by the motion of the observer.

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25
Q

How would you use the method of heliocentric parallax?

A

Measure the angular displacement of a nearby star over a period of 6 months.
Halve this angle to get the parallax angle.
Determine distance to the star using the formula d=1/p.

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26
Q

How does heliocentric parallax work?

A

Distant stars do not appear to move as much as closer stars, because their angular displacement is too small.
Therefore, nearby stars appear to jump against a background of distant stars.
This is due to the orbital motion of earth around the sun.

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27
Q

What is a parsec?

A

The distance at which a star would have a parallax angle of 1 arcsec.

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28
Q

What is absolute magnitude?

A

The apparent magnitude of a star from a distance of 10 parsecs.

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29
Q

Does the inverse square law of light apply to other electromagnetic radiation, or just light?

A

It also applies to other electromagnetic radiation.

30
Q

If a star is 2x further away, how many times dimmer does it appear?

A

4x

31
Q

What is the distance modulus formula?

A

M=m+5-5logd

32
Q

In the distance modulus formula, what is the unit of distance?

A

parsecs

33
Q

What is a Cepheid variable star?

A

A giant yellow star that regularly expands and contracts in size.

34
Q

What are Cepheid variable stars named after?

A

The prototype Cep.

35
Q

Why does light intensity of a Cepheid variable star change?

A

Because it is pulsating, due to the regular ionisation of helium.

36
Q

What does the light curve of a Cepheid variable look like?

A

Has a sharp rise and a slow decay.

37
Q

What can the period of a Cepheid variable star vary from?

A

Hours to years

38
Q

What is a light curve?

A

A graph showing how light intensity varies over time.

39
Q

Who determined the period-luminosity law, and when?

A

American astronomer Henrietta Leavitt, in 1912.

40
Q

What did Henrietta Leavitt observe?

A

A large number of Cepheid variable stars in the Small Magellanic Cloud.

41
Q

What is the limitation of the method of heliocentric parallax to determine the distance of stars?

A

It only works with relatively nearby stars.

42
Q

How would you determine the distance of a more distant, non-Cepheid variable star?

A

Use the light curve of a nearby Cepheid variable star to determine pulsation period.
Use the period-luminosity law to determine mean absolute magnitude.
Find its apparent magnitude.
Use the distance modulus formula to determine distance in parsecs.
Compare spectra with the non-Cepheid variable star to determine redshift, and therefore distance of the non-Cepheid Variable star.

43
Q

What is a binary star?

A

Two stars orbiting their common centre of mass.

44
Q

What is the primary star, and what is the secondary star?

A

The primary star is brighter, the secondary or companion star is dimmer.

45
Q

What does it mean when the light curve of an eclipsing binary star has steady light intensity?

A

The two stars are side by side.

46
Q

What happens when a primary star eclipses the secondary star?

A

There is a smaller dip in light intensity.

47
Q

What happens when the secondary star eclipses the primary star?

A

There is a bigger dip in light intensity.

48
Q

What happens when size, temperature and radius are the same?

A

The two dips in light intensity are the same.

49
Q

What happens when temperature and radius but not mass are the same?

A

The two dips in intensity are the same.

50
Q

What happens when temperature and mass but not radius are the same?

A

The two dips in intensity are the same, but are less sharp and have more of a ‘square’ base.

51
Q

What happens when radius and mass but not temperature are the same?

A

There are two dips of which one is greater.

52
Q

What happens when a binary system has an eccentric orbit?

A

The two dips will be closer together.

53
Q

What are absorption lines created?

A

Absorption lines correspond to known wavelengths of light where electrons of elements, ions and molecules in the outer layers of the star / corona absorb enough energy to jump shells.

54
Q

What did Isaac Newton do?

A

He split light into its component wavelengths using a prism.

55
Q

What do modern astronomers use to analyse light?

A

A diffraction grating.

56
Q

How to you determine chemical element using absorption lines?

A

Look at its position in relation to other lines.

57
Q

Why can you determine the temperature of a star from its spectrum?

A

Colour, and therefore the pattern of absorption lines visible, determine temperature.

58
Q

List the information you can get from a spectrum.

A 
Chemical composition
Temperature
Radial velocity
Existence of exoplanets/companion stars
Age
Rotation rate
59
Q

What is the Harvard scheme?

A

The classification of stars according to luminosity using the groups OBAFGKM and divisions 1-9.

60
Q

Give an example of each spectral type.

A 
O=Zeta Orionis
B=Rigel
A=Vega
F=Polaris
G=Sol
K=Arcturus
M=Antares
61
Q

Which is the hottest spectral type?

A

O

62
Q

What is the rarest spectral type, and what is its rarity?

A

O, 1 in 3 million

63
Q

What are the colours of each spectral type?

A 
O=blue
B=blue
A=blue-white
F=white
G=yellow-white
K=yellow
M=orange
64
Q

What are the smallest spectal types, and are there exceptions?

A

KM are the smallest, but there can also be several red giants or supergiants (Arcturus and Antares).

65
Q

Why does colour change with temperature?

A

Heating objects causes a change in poistion of absoption lines because energy given out changes. When objects are heated, light is first IR, then red, then orange, then yellow, then white, then blue and then UV , which cannot be seen.

66
Q

Why are there no purple stars?

A

The human eye is more sensitive to blue than purple. And because a star that emits purple light also emits blue light, we detect blue first.

67
Q

Who devised the Hertzprung-Russel diagram, and when?

A

Danish Ejnar Hertzprung and American Henry Russel in the early 20th century.

68
Q

What is a HR diagram?

A

A diagram of spectral type against temperature/luminosity, that shows the evolutionary sequence of stars.

69
Q

What is luminosity?

A

The amount of energy emitted by a star in a given time.

70
Q

What types of stars are classified on the HR diagram?

A

Main sequence, supergiant, red giant, white dwarf, brown dwarf and black dwarf.

71
Q

Which stars on the HR diagram have the longest lifespan?

A

The low-mass stars on the bottom right, which are less luminous and run out of fuel less quickly.

Astronomy GCSE (7 decks)

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