Astrophysics Flashcards

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1
Q

Draw a Hertzsprung Russel Diagram

A
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2
Q

Describe the lifecycle of stars

A
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3
Q

Describe the future of our Sun

A

The Sun is fusing/burning hydrogen (into helium in its core)

When (hydrogen) fusion/burning ceases the core of the Sun cools [accept radiation pressure drops when fusion/burning ceases in the core]

The core collapses/contracts (under gravitational forces)

The Sun expands and becomes a red giant

The core becomes hot enough for helium fusion/burning to begin (in the core) Helium begins to run out and the core collapses again (under gravitational forces)

Idea that outer layers of Sun are ejected into space The temperature doesn’t rise enough for further fusion to begin The core/Sun becomes a (white) dwarf star

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4
Q

Cosmological Reshift Model Answer

A

Redshift is the (fractional) increase in wavelength received (by an observer)

Due to source and observer receding (from each other)

Measure frequency/wavelength of light (from the galaxy)

Compare (measured) frequency/wavelength to the frequency/wavelength for a source on the Earth

States appropriate Doppler formula (consistent with mp1/mp2) and how it is used to calculate velocity

Appropriate reference to Hubble’s Law Or v = HOd

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5
Q

Give the equation linking redshift and v

A

z = Δλ/λ = Δf/f = v/c where

Δλ is the change in wavelength, λ is original wavelength

Δf is the change in frequency, f is the original frequency

v is the recessional velocity, c is the speed of light

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6
Q

Sketch Hubble’s Graph and state the gradient

A

The gradient H0 - Hubble’s Constant

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7
Q

Explain how the age of the universe is found

A

Hubble’s Law states v = H0d

Imagine a galaxy moving away from us at velocity v since the beginning of the universe, therefore time t.

The distance the galaxy is moving away from us is vt

Substituting into Hubble’s Law v = H0vt => 1/H0 = t

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8
Q

State Hubble’s Law

A

v = H0d

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9
Q

Give the equation for Intensity

A

Intensity = Pressure/Area

I = P/A

I = L/4πd^2

where L is luminosity and d is distance

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10
Q

Standard Candles Model Answer

A

A standard candle is a (stellar) object of known luminosity

Object must be commonly found in the universe

Standard candle’s flux/ brightness (on Earth) is measured/determined

Use inverse square law [Reference to F=L/4πd2 with symbols defined]

(Hence) distance to the standard candle is calculated/determined

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11
Q

Parallax Model Answer

A

The star is viewed from two positions at 6 month intervals Or opposite ends of its orbit diameter about the Sun

The change in angular position of the star against background of fixed stars is measured

Trigonometry is used to calculate the distance to the star [Do not accept Pythagoras]

The diameter/radius of the Earth’s orbit about the Sun must be known

If star is too distant the angle is too small to measure

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12
Q
A
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