3.3 : Physical Properties of Stars

Do stars in a constellation have any physical links?
No -- their apparent relation is merely a line-of-sight effect.
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Do stars in a cluster have any physical links?
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Are optical double stars closely-aligned?
No, they only appear to be. They can be very far apart in reality.
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Are binary stars closely-aligned?
Yes -- they are the same distance from Earth and orbit their common centre of gravity (mass).
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What is stellar magnitude?
A measure of a star's brightness.
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What does a magnitude difference of 1 between two stars tell you about the stars?
One appears 2.5x brighter than the other.
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What factors does a star's apparent magnitude (m) depend on?
The total energy radiated by the star (this depends on its size and temperature); the distance to the star; the amount of interstellar dust and gas; the amount of light absorbed by Earth's atmosphere.
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What is the mathematical link between a star's brightness and its distance from Earth?
An inverse square law.
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What is absolute magnitude (M)?
The apparent magnitude a star would have if observed from a standard distance of 10 parsecs.
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What is the distance modulus formula?
M = m + 5 - 5log(d)
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What is a variable star?
A star whose emitted radiation varies in intensity on a regular basis.
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What are the two main classes of variable star?
Binary stars (two stars orbiting around their common centre of mass) and Cepheid variables (giant yellow stars that regularly expand and contract in size).
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What are light curves and what can they be used to determine?
Light curves are graphs showing how the intensity of light from a variable star changes with time. They can be used to determine the period of variability.
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In a binary system, which star is the primary and which is the secondary?
The primary is the brighter star and the secondary is the dimmer star.
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When does an eclipsing binary occur?
If the stars orbit in a plane along our line of sight.
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What causes variable light intensity in a binary system?
The stellar motion of the stars.
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What is the period of variability for binary stars?
14 days.
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What causes variable light intensity in a Cepheid variable?
Its pulsation -- the changing size and temperature impact the luminosity of the star.
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What is the period of variability for a Cepheid variable?
6.5 days.
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Why can't the radar technique be used to measure the distances to stars?
The distances are so large that it would take years to receive the 'return' signal; the 'return' signal would be so weak that it would be undetectable from background radiation; stars are spheres of gas and do not have hard reflecting surfaces.
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What is parallax?
The apparent motion of near and more distant objects with respect to one another (nearer objects appear to move much more quickly).
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What causes parallax between stars?
The Earth's orbital motion around the Sun.
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How can heliocentric parallax be used to determine the distance to a star?
The distance is given by 1 / p, where p is the parallax angle (half of the star's angular shift) in arcsec.
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How can the period-luminosity law be used to determine the distance to a star?
The law allows the star's absolute magnitude to be determined, which can then be used in the distance modulus formula.
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Other cards in this set

Card 2

Front

Do stars in a cluster have any physical links?

Card 3

Front

Are optical double stars closely-aligned?

Card 4

Front

Are binary stars closely-aligned?

Card 5

Front

What is stellar magnitude?