astrophysics

Question 1

what is spatial resolution?

Answer 1

how far apart different parts of an object need to be in order for them to be distinguishable

Question 2

what is meant by the Rayleigh criterion?

Answer 2

two objects will just be resolved if the first minnimum of the airy disc in the diffraction pattern of one image coincides with the central maxima of the airy disc of the other

Question 3

Explain how an orbiting planet causes a Doppler shift in the spectrum of a star.

Answer 3

Planet and star orbit around common centre of mass that means the star moves towards/away from Earth as planet orbits

Causes shift in wavelength of light received from star

Question 4

State two advantages of using an astronomical telescope that has a large diameter objective lens

Answer 4

• Large diameter allows fainter objects to be viewed(as the collecting power is proportional to d2)
• Larger diameter allows better resolution (as smallest resolvable angle is proportional to 1 / d)

Question 5

state the cosmological principle

Answer 5

on a large scale the universe is homogeneous (every part is the same as every other part) and isotropic (everything looks the same in every direction)

Question 6

what is cosmological microwave background radiation?

Answer 6

It is the radiation coming from all parts of the Universe

Question 7

what is the Doppler effect?

Answer 7

the apparent change in frequency of a wave due to the relative motion of the source and observer

Question 8

what is the schwarzschild radius?

Answer 8

the radius of a black hole

Question 9

Describe the structure and operation of the CCD and discuss the advantages of using a CCD for astronomical observations

Answer 9

• The CCD is a silicon chip
• The chip is divided into picture elements
• Each picture element is associated with a potential well in the silicon
• Incident photons are focused on the CCD
• The photons cause the release of electrons within the semiconductor
• The number of electrons liberated is proportional to the intensity of the light.
• Electrons are trapped in the potential wells
• An electron pattern is built up which is identical to the image formed on the CCD
• When exposure is complete the charge is processed to form an image.

Advantages:
High quantum efficiency > 80%
Light integration – using long exposure times to capture faint images.
Device can be directly linked to computer for capture and analysis.

Question 10

what is a solar mass?

Answer 10

the mass of the sun

Question 11

State what is meant by the Hubble constant.

Answer 11

Gives the ratio of the (recessional) velocity (of galaxies) to distance from Earth

Question 12

What property of quasars led to their discovery?

Answer 12

(Strong) radio sources

Question 13

State what is meant by the Doppler effect.

Answer 13

change in (apparent) frequency [or wavelength] (1)
due to relative motion between source and observer