Space (10) Flashcards
What happens to light as it leaves the surface of a star?
It spreads out uniformly through a spherical shell.
What is the formula for the surface area of a sphere?
4πr^2.
What do the symbols in the inverse square law represent
F=radiant flux
L=luminosity
d=distance from star
What assumptions does the inverse square law equation make?
1) The star radiates power uniformly through space
2)No radiation is absorbed between the star and Earth
What does the inverse square law tell us about luminosity?
The luminosity L of a star is constant regardless of distance.
What is the principle of parallax based on?
It is based on how the position of an object appears to change as the position of the observer changes.
What is stellar parallax used for?
It is used to measure the distance to nearby stars.
Define stellar parallax.
The apparent shifting in position of a nearby star against a background of distant stars when viewed from different positions of the Earth during its orbit around the Sun.
Why do nearby stars appear to shift in position over time?
Because the Earth changes position as it orbits the Sun, causing closer stars to appear to move relative to distant stars.
Why do distant stars not appear to move?
Because they are much farther away, making their apparent motion negligible.
What is the relationship used to calculate stellar parallax?
tan(p)=AU/d , where AU is the radius of Earth’s orbit, p is the parallax angle, and d is the distance to the star.
When are stellar parallax observations typically made?
In January and again in July, six months apart, to maximize the distance the Earth has moved.
What simplification is used for small angles in stellar parallax calculations?
tan(p)=p, so the equation simplifies to p=AU/d
What is the equation for measuring stellar distances in parsecs?
p=1/d
(p is parallax angle in arc-seconds, and d is the distance in parsecs
Why is stellar parallax only accurate for distances up to 100 parsecs?
Because for distances larger than 100 parsecs, the angles involved become so small that they are difficult to measure accurately.
What is a standard candle
A stellar object with known luminosity
Give two examples of standard candles
Cepheid variable stars and Type 1a supernovae
How do Cepheid variable stars act as standard candles
Their brightness varies over a set period, and this variation has a well-defined relationship with their luminosity
Why are Type 1a supernovae useful as standard candles?
The luminosity at the time of the explosion is always the same, making them reliable distance indicators
Why is measuring astronomical distances challenging
A direct measurement is only possible for objects close to Earth, requiring indirect methods for distant objects
How do standard candles help measure distances
If the luminosity is known, the distance can be estimated based on how bright the object appears from Earth
What is the cosmic distance ladder
A method where different distance measurement techniques are combined to determine the scale of the universe
What are the axes on the Hertzsprung-Russell diagram?
Y-axis: Luminosity (dim at the bottom, bright at the top); X-axis: Temperature (hot on the left, cool on the right).
What did Hertzsprung and Russell discover about stars?
Stars cluster in distinct areas on the diagram, with most forming a band called the main sequence.
What is the relationship between luminosity and temperature for main sequence stars?
Luminosity increases with surface temperature.
Where are red giants and red supergiants located on the H-R diagram, and why?
Above the main sequence; they are very luminous but cooler, meaning they must be much larger than main sequence stars.
Where are white dwarfs located on the H-R diagram, and why?
Below and to the left of the main sequence; they are hot but not very luminous, meaning they must be much smaller.
Why don’t black holes appear
They emit no light, making them invisible on the diagram.
What determines the life cycle of a star?
The initial mass of the star.
What are the first four stages in the life cycle of all stars?
1) Nebula, 2) Protostar, 3) Nuclear Fusion, 4) Main Sequence Star.
What is a nebula?
A giant cloud of hydrogen gas and dust where stars form due to gravitational collapse.
How does a protostar form?
Gravitational collapse heats up the gas and dust, causing it to glow and form a protostar
What happens when a protostar reaches millions of degrees Kelvin?
Nuclear fusion begins, converting hydrogen into helium.
What happens in the main sequence stage of a star?
The inward force of gravity and outward pressure from nuclear fusion reach equilibrium, making the star stable.
Why does a red giant form?
fusion slows, and the outer layers expand and cool.
What happens to a low-mass star after the main sequence stage?
It becomes a red giant, then a planetary nebula, and finally a white dwarf.
What happens to a high-mass star after the main sequence stage?
It becomes a red supergiant, then undergoes a supernova explosion, forming either a neutron star or a black hole.
What is a supernova?
A massive explosion that occurs when a high-mass star’s iron core collapses.
What determines whether a supernova remnant becomes a neutron star or a black hole?
If the core mass is less than 3 solar masses, it becomes a neutron star; if greater, it collapses into a black hole.
What is a white dwarf?
The hot, dense core left behind after a low-mass star ejects its outer layers as a planetary nebula.
What happens to wavefronts when a wave source is stationary
They spread out symmetrically.
What happens to wavefronts when a wave source is moving?
The waves become squashed together in front of the source and stretched out behind it.
What is the observed effect when a wave source moves toward an observer?
The wavefronts appear squashed, meaning the wavelength decreases, and the frequency increases.
What is the observed effect when a wave source moves away from an observer?
The wavefronts appear stretched out, meaning the wavelength increases, and the frequency decreases.
What is the Doppler effect?
The apparent shift in wavelength occurring when the source of the waves is moving.
How can the Doppler effect be observed in space?
By comparing the light spectrum of a nearby object, like the Sun, with that of a distant galaxy.
What does redshift in the light from distant galaxies indicate?
The universe is expanding.
Hubble’s constant=
recessional velocity of an object/distance between object and the Earth
Why is it difficult to be certain about how accurate Hubble’s constant is
Random and systematic errors involved when calculating the distance to a galaxy or star
For small mass systems like planets, what happens when the object moves away from the galaxy’s centre
Velocity decreases as there is a weaker gravitational field strength felt
For large mass systems like planets, what happens when the object moves away from the galaxy’s centre
Velocity remains constant
Is mass concentrated in the centre of a galaxy
No, it’s spread out
All observable mass is concentrated in the centre of the galaxy, what does this mean
There is another type of mass, (dark matter)
How is dark matter defined
Matter which cannot be seen and that does not emit or absorb electromagnetic radiation
How much of the universe does dark matter make up
27%
How is dark matter detected
Based on its gravitational effects relating to the rotation of galaxies
