Topic 10 - Space Flashcards
What is an Astronomical Unit(AU)?
- Mean distannce between the Earth and Sun
What is a light year?
- Distance travelled by an EM wave through space in one year
- Equal to 63000AU
What is parallax?
- The apparent in position of an object depending on the vewing angle
- Change in position is measured as the parallax angle
How can you use parallax measurements to calculate the distance of an object from the Earth?
- The object is viewed from two positions whilst the Earth is on opposite ends of its orbit diameter around the Sun.
- The change in angular position against the background of fixed stars in measured
- Trigonometry is used to calculate distance to star
What is the limitation of using parallax measurements?
- If stars are too far away the angular displacement is too small to measure
What is a parsec?
- Distance to a star whose parallax angle is 1 arcsecond
- 3.09x10^16
What is luminosity?
- Total energy a star emits in one second
How can you calculate luminosity?
- Stefan-boltzmann law: L=4πr^2σT^4
- Where σ is the steffan boltzmann-constant
- Where T is the surface temperature of the star (in Kelvin)
- Where r is the radius of the star
What is intensity?
- Power of radiation incident on Earth from star per square meter.
How can you calculate intensity?
- Inverse square law: I = L/(4πd^2)
- Where d is the distance from the object to Earth
What is a standard candle?
- A stellar object of known luminosity
How can standard candles be used to calculate distances?
- Standard candle has known luminosity
- Standard candle’s flux on Earth is measured
- Use inverse square law
- Distance to standard candle is calculated and used as a reference to find out other distances
What is Wein’s Law?
- λ(max)T= 2.9x10^-3
What is a Hertzsprung-Russel (H-R) diagram?
- Visual represntation of lifecycle of a star
- A plot of luminosity against surface temperature
What is the lifecycle of a star with similar mass to the sun?
- Stellar nebula
- Protostar
- Main Sequence
- Red Giant
- White dwarf
- Black dwarf
What is the lifecycle for a star with mass between 1.4 and 3 times solar masses?
- Stellar nebula
- Protostar
- Main Sequence
- Red Supergiant
- Supernova
- Neutron Star
What is the lifecycle for a star with mass greater than 3 times solar masses?
- Stellar nebula
- Protostar
- Main Sequence
- Red Supergiant
- Supernova
- Black Hole
How is a protostar formed?
- Clouds of gas and dust (nebulae) clump together under gravity
- Clumps form a denser centre
- Temperature increases as star gets denser
How is a main sequnce star formed?
- Once temperature of protostar is high enough fusion of hydrogen nuclei begins
- Outwards force due to fusion and gravity are in equilibrium
- Greater the mass of the star the shorter its main sequnce stage
How is a Red Giant formed?
- Once hydrogen fuel in main sequnce star runs out temperature of core increases under weight of star
- Fusion of helium begins
- Outer layers expand and cool
How are white dwarfs formed?
- Once helium fuel in a Red Giant runs out, star collapses under its own weight again
- Core shrinks and ejects its outer layers leaving behind a white dwarf
How are Supernova formed?
- When all fuel runs out core collapses inwards and becomes rigid as it cant be compressed further
- Outer layers fall inwards and rebound off the core into space in a shockwave
How are neutron stars formed?
- When core of a larger star collapses gravity is so strong it forces electrons and protons together to form neutrons
How are black holes formed?
- When core of a giant star collapses neutrons are unable to withstand the force of gravity forcing them together
