Non-Optical Telescopes

Question 1

State the 2 least effected areas of the electromagnetic spectrum from ground-based observations

Answer 1

Visible light

Radio-waves

Question 2

Describe the design of a single dish radio telescope

Answer 2

It is very similar to a reflecting optical telescope. The parabolic metal surface (reflecting dish) reflects the radio-waves to an aerial without any spherical aberration. There is no need for a secondary reflector since the aerial can be placed at the focal point

Question 3

State forms of interference for radio telescopes which make the detection of extra-terrestrial objects difficult, and state ways in which they can be reduced

Answer 3

Interference: Radio transmissions, mobile phones, radar systems, global navigation satellites, satellite TV and microwave ovens
Reduction:
- building radio telescopes away from centres of population
- Linking telescopes together removes local interference and enhances the common signal from the distant source

Question 4

State and explain one way in which the cost of the reflecting dish of a radio telescope can be reduced

Answer 4

Making the reflecting dish from mesh rather than solid metal reduces the cost and weight
This is because radiowaves are relatively long, so mesh can be used as long as the mesh size is smaller than λ/20, so the radiowaves are reflected rather than diffracted through the mesh

Question 5

Give an example of an infrared detecting telescope, its position and examples of its uses

Answer 5

• UKIRT
• 4200m above sea level on Mauna Kea, Hawaii
• Finding exoplanets, observing after-effects of gamma ray bursts and observing nebulae

Question 6

Give an example of an ultraviolet detecting telescope, its position and examples of its uses

Answer 6

• GALEX
• Low Earth orbit (ht 700km)
• Star formation rate in distant galaxies, analysing quasars

Question 7

Give an example of an X-ray detecting telescope, its position and examples of its uses

Answer 7

• Chandra
• Earth obit (ht 140,000km)
• Discovering supermassive black holes, observing stellar remnants

Question 8

Give 3 reasons that many modern telescopes are put into space

Answer 8

• The absorption of the electromagnetic waves by the atmosphere
• The light pollution and other interference at ground level
• The effect the atmosphere has on the path of the light as it passes through

Question 9

State the effect of increasing the diameter of the reflecting dish

Answer 9

It would improve both the resolving power, as well as increasing the collecting power (the rate at which energy can be collected by the telescope)