Astrophysics

Question 1

Define Absolute Magnitude

Answer 1

The apparent magnitude a star would have from a distance of 10 parsecs away

Question 2

Define Apparent Magnitude

Answer 2

The apparent brightness of a star from Earth (or the eye) expressed on the magnitude scale

Question 3

Define Airy Disc

Answer 3

The bright central fringe of a refraction pattern from light entering a circular aperture

Question 4

Name the order of the Spectral Class (hottest to coldest)

Answer 4

O, B, A, F, G, K, M

Question 5

Define an Absorption Spectrum (in context of stars)

Answer 5

A pattern of dark spectral lines in a continuous spectrum produced by the absorption of photons of precise energy which causes changes within an atom

Question 6

State the Order of the life of a small star (like our Sun)

Answer 6

Interstellar Cloud, Protostar, Main Sequence, Red Giant, Planetary Nebula, White Dwarf.

Question 7

State the colour, Spectral Class and some elements within the temperature range of 7500-11000K

Answer 7

Colour: Blue or White (or Bluish White)
Spectral Class: A
Elements: Hydrogen and Ionised Metals

Question 8

Define Quantum Efficiency

Answer 8

The ratio of photons detected to photon incident (no. of photons arriving and absorbed/total arriving)

Question 9

Define a Standard Candle

Answer 9

An astronomical object of known intrinsic brightness, for example a supernova that is used to determine astronomical distances.

Question 10

Explain Schwarzschild Radius

Answer 10

The radius of a black hole between the singularity and the event horizon. The event horizon is where the escape velocity equals to (or greater than) the speed of light.

Question 11

Name the traits of a Neutron Star

Answer 11

• Small
• Dense
• Has a core made of nuclear matter (or neutrons)

Question 12

What is Collecting Power proportional to?

Answer 12

Collecting Power is proportional to the objective diameter squared

Question 13

Name 2 disadvantages of a refracting telescope

Answer 13

• Experiences Chromatic Aberration
• Experiences Spherical Aberration
• High cost (compared to reflecting)
• Usually heavier than reflecting (due to lenses being heavier than mirrors)

Question 14

What is Pogson’s Law expressed as?

Answer 14

m2 - m1 = 2.5 log (base 10) (b2/b1)

Question 15

What is a parsec?

Answer 15

It is the distance at which the observed parallax angle of the star is equal to 1 arc second.

Question 16

What does parallax mean?

Answer 16

The effect whereby the position or direction of an object appears to differ when viewed from different positions.

Question 17

Define Stephan’s Law

Answer 17

A body, when heated, will emit electromagnetic radiation over a range of wavelengths with a total intensity that is proportional to the fourth power of its absolute temperature.

Question 18

Define Wien’s Displacement Law

Answer 18

The wavelength of the peak emission intensity is inversely proportional to the absolute temperature of the object.

Question 19

What does the term black body mean?

Answer 19

A body that absorbs all the radiation incident upon it and reflects none.

Question 20

What energy level do hydrogen atoms from the Balmer series excite to?

Answer 20

n=2

Question 21

What are the coldest and hottest colours for stars?

Answer 21

Hottest stars = Blue

Coldest stars = Red (Orange)

Question 22

What is a protostar?

Answer 22

It is a star in its earliest form of life, from a dense cloud of gas, prior to fusion reactions within the core.

Question 23

What are the characteristics of the following:
Red giants
Supergiants
White dwarves

Answer 23

Red giants –> Cooler and redder stars. Nuclear fusion of helium occurs in the core, similar mass to that of the sun but with an expanded outer shell.

Supergiants –> Mass typically around 10-100 times that of the sun. Core temperatures are hot enough for nuclear fusion to produce carbon and heavier elements. Also more luminous than other stars.

White dwarves –> Old stars that have a high surface temperature but are not very luminous. Do not generate energy by nuclear fusion, however extremely dense.

Question 24

Which spectral class of stars have the greatest main sequence lifespans?

Answer 24

Spectral class M (Potentially over 200,000,000,000 years)

Question 25

What does a star need to create a supernova?

Answer 25

It requires a mass 1.4 times greater than that of the sun.

Question 26

What does it mean by a type II supernova?

Answer 26

This is a single star, a red giant or supergiant that runs out of nuclear fuel and collapses rapidly under its own gravity, ejecting its outer layers with enormous energy.

Question 27

What do we call the exotic object at the centre of the supernova remnants?

Answer 27

A neutron star

Question 28

Define escape velocity

Answer 28

The speed necessary for an object to escape the gravitational pull of another object, such as a planet or star.

Question 29

Define black hole

Answer 29

It is a region of space-time that has such a strong gravitational field that no particles or electromagnetic radiation can escape from it. (greater than the speed of light)

Question 30

What is a gamma ray burst and why are they potentially dangerous?

Answer 30

These are thought to be narrow beams of intense radiation that came from a collapse of a supernova. They are potentially dangerous as if they were on a collision course with the Earth it could cause mass extinction.

Question 31

What is the order of life for a massive star?

Answer 31

Interstellar cloud - protostar - main sequence (for about 10 million years - red giant/super giant - supernova - either a black hole or a neutron star.

Question 32

What is a type I supernova?

Answer 32

This is a star that accretes (draws in) matter from another star in a binary system until it becomes compressed and runaway nuclear reactions are set off, blasting its matter into space.