Astrophysics Flashcards
Draw a Hertzsprung Russel Diagram
Describe the lifecycle of stars
Describe the future of our Sun
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
Cosmological Reshift Model Answer
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
Give the equation linking redshift and v
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
Sketch Hubble’s Graph and state the gradient
The gradient H0 - Hubble’s Constant
Explain how the age of the universe is found
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
State Hubble’s Law
v = H0d
Give the equation for Intensity
Intensity = Pressure/Area
I = P/A
I = L/4πd^2
where L is luminosity and d is distance
Standard Candles Model Answer
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
Parallax Model Answer
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
