Topic 10 - Space

Question 1

What is an Astronomical Unit(AU)?

Answer 1

• Mean distannce between the Earth and Sun

Question 2

What is a light year?

Answer 2

• Distance travelled by an EM wave through space in one year
• Equal to 63000AU

Question 3

What is parallax?

Answer 3

• The apparent in position of an object depending on the vewing angle
• Change in position is measured as the parallax angle

Question 4

How can you use parallax measurements to calculate the distance of an object from the Earth?

Answer 4

• 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

Question 5

What is the limitation of using parallax measurements?

Answer 5

• If stars are too far away the angular displacement is too small to measure

Question 6

What is a parsec?

Answer 6

• Distance to a star whose parallax angle is 1 arcsecond
• 3.09x10^16

Question 7

What is luminosity?

Answer 7

• Total energy a star emits in one second

Question 8

How can you calculate luminosity?

Answer 8

• 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

Question 9

What is intensity?

Answer 9

• Power of radiation incident on Earth from star per square meter.

Question 10

How can you calculate intensity?

Answer 10

• Inverse square law: I = L/(4πd^2)
• Where d is the distance from the object to Earth

Question 11

What is a standard candle?

Answer 11

• A stellar object of known luminosity

Question 12

How can standard candles be used to calculate distances?

Answer 12

• 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

Question 13

What is Wein’s Law?

Answer 13

• λ(max)T= 2.9x10^-3

Question 14

What is a Hertzsprung-Russel (H-R) diagram?

Answer 14

• Visual represntation of lifecycle of a star
• A plot of luminosity against surface temperature

Question 15

What is the lifecycle of a star with similar mass to the sun?

Answer 15

• Stellar nebula
• Protostar
• Main Sequence
• Red Giant
• White dwarf
• Black dwarf

Question 16

What is the lifecycle for a star with mass between 1.4 and 3 times solar masses?

Answer 16

• Stellar nebula
• Protostar
• Main Sequence
• Red Supergiant
• Supernova
• Neutron Star

Question 17

What is the lifecycle for a star with mass greater than 3 times solar masses?

Answer 17

• Stellar nebula
• Protostar
• Main Sequence
• Red Supergiant
• Supernova
• Black Hole

Question 18

How is a protostar formed?

Answer 18

• Clouds of gas and dust (nebulae) clump together under gravity
• Clumps form a denser centre
• Temperature increases as star gets denser

Question 19

How is a main sequnce star formed?

Answer 19

• 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

Question 20

How is a Red Giant formed?

Answer 20

• 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

Question 21

How are white dwarfs formed?

Answer 21

• 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

Question 22

How are Supernova formed?

Answer 22

• 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

Question 23

How are neutron stars formed?

Answer 23

• When core of a larger star collapses gravity is so strong it forces electrons and protons together to form neutrons

Question 24

How are black holes formed?

Answer 24

• When core of a giant star collapses neutrons are unable to withstand the force of gravity forcing them together