Astrophysics

Question 1

What are disadvantages of refracting telescopes?

Answer 1

Chromatic and spherical aberration.
Distortion due to warping of glass.
Expensive.

Question 2

What is chromatic aberration?

Answer 2

Different wavelengths focus at different points causing blurred image.

Question 3

What is spherical aberration?

Answer 3

Spherical lens means rays focus at different points.
Closer to centre of lens = focuses further away.

Question 4

Which colour of light focuses furthest from lens due to chromatic aberration?

Answer 4

Red.

Question 5

What is resolving power / Rayleigh criterion?

Answer 5

Minimum angle at which two objects are able to be differentiated between.
Central maximum of one sits over the first minimum of the other.

Question 6

What is quantum efficiency?

Answer 6

Number of photons detected / Number of photons incident x 100

Question 6

What is a CCD and how does it work?

Answer 6

Silicon chip divided into pixels.
Incident light liberates electrons which are trapped in potential wells.
Number of electrons liberated is proportional to intensity of light.
Pattern built up by electrons forms image.

Question 7

What is the quantum efficiency of a CCD?

Answer 7

Around 70%

Question 8

What is the gathering power?

Answer 8

Energy / photons collected per second.

Question 9

What is brightness of a telescope proportional to?

Answer 9

d^2

Question 10

What is luminosity

Answer 10

Total energy emitted per second (power).

Question 11

What number is used to compare the brightness of stars?

Answer 11

2.512

Question 12

What is a parsec?

Answer 12

Distance an object must be to have a parallax of one arcsecond when observed from Earth.

Question 13

What is a light year?

Answer 13

Distance an EM wave travels in a year.

Question 14

What is apparent magnitude?

Answer 14

Magnitude of a star as seen from Earth.

Question 15

What is spacial resolution?

Answer 15

How far apart objects need to be to be distinguishable.

Question 16

What is a blackbody?

Answer 16

Absorbs and can emit all wavelengths of EM radiation.

Question 17

What is the area under a black body curve?

Answer 17

Intensity.

Question 18

Which telescopes cannot be grounded on Earth?

Answer 18

Infrared
UV
X-Ray
Gamma

Question 19

What do lines on absorption spectrum refer to?

Answer 19

Photons absorbed by gases.

Question 20

What do lines on an emission spectrum refer to?

Answer 20

Photons emitted from energy levels.

Question 21

Where do electrons with a high temp reside in for Balmer series?

Answer 21

n=2 level, so strong lines.

Question 22

Where do electrons with a low temp reside in for Balmer series?

Answer 22

n=1 level, so weak lines.

Question 22

Where do electrons with a very high temp reside in for Balmer series?

Answer 22

n=3 level, so less strong lines.

Question 23

What is the lifetime of a star similar in mass to our Sun?

Answer 23

- Gas cloud - Main sequence (H burning) - Red giant (He burning) - Dwarf

Question 24

What is Hydrogen burning?

Answer 24

Fusion of Hydrogen into Helium.

Question 24

What is radiation pressure?

Answer 24

Pressure exerted upon any surface with EM radiation.

Question 25

What will a star < 1.4 solar masses turn into?

Answer 25

White dwarf

Question 26

What will a star > 3 solar masses turn into?

Answer 26

Black hole

Question 26

What will a star > 1.4 solar masses turn into?

Answer 26

Neutron star

Question 27

What is the neutron degeneracy force?

Answer 27

Repulsive strong nuclear force, counteracts inwards gravity.

Question 28

What is the Schwarzschild radius?

Answer 28

Radius at which light cannot escape a black hole.

Question 28

How does a type 1a supernova occur?

Answer 28

- White dwarf steals energy from a close star. - Gains mass and collapses at 1.4 solar masses. - High temp means carbon can be fused. - Undergoes nuclear fusion and explodes in supernova.

Question 29

What is a standard candle?

Answer 29

An object of known luminosity.

Question 30

If the apparent frequency of a star is less than the true frequency of a star what happens?

Answer 30

Red shifted.

Question 30

If the apparent frequency of a star is greater than the true frequency of a star what happens?

Answer 30

Blue shifted.

Question 31

What are the units for velocity and distance in Hubble's law?

Answer 31

km/s and Mpc

Question 32

What are 3 pieces of evidence of the big bang?

Answer 32

- Expansion of the universe. - Cosmic microwave background radiation. - Relative abundance of H and He.

Question 33

What is CMB?

Answer 33

High frequency radiation released after big bang when matter and radiation 'decoupled' (universe cooled). Variations are thought to be seeds of galaxies.

Question 34

How does red shift support the big bang theory?

Answer 34

Galaxies further away are accelerating away from us. Reverse time back puts all matter and universe into one place, universe started from one infinitely dense and hot point.

Question 35

How does the relative abundance of H and He support the big bang theory?

Answer 35

H to He is 3:1. Early universe was hot enough to fuse He but cooled too quickly to fuse anything heavier.

Question 36

What is a quasar?

Answer 36

Active galactic nuclei, supermassive black hole at the centre of the galaxy.

Question 37

How is a quasar formed?

Answer 37

Gravitational pull of material is so strong that the collisions of these in the accretion disk produce extremely high amounts of radio (high energy) waves.

Question 38

How were quasars discovered?

Answer 38

High levels of high frequency radiation. Brightest celestial objects in universe, jets of radiation shoot out either side.

Question 39

What is an exoplanet?

Answer 39

A planet that orbits a star outside of our solar system.

Question 40

What are the two methods of detecting exoplanets?

Answer 40

Transit and radial velocity / doppler.

Question 41

Describe the radial velocity / doppler method of detecting an exoplanet.

Answer 41

Orbits centre of mass which makes star wobble. If wobble is aligned to our line of sight, red and blue shifts will be seen.

Question 42

Describe the transit method of detecting an exoplanet.

Answer 42

As planet moves between the observer and the star, apparent magnitude will change (dip in light curve).

Question 43

What is absolute magnitude?

Answer 43

Magnitude of a star if it was 10 parsecs from Earth.