Answer to Question #142547 in Astronomy | Astrophysics for Kai

Question

The star Wolf 359 is at a distance of 7.8 light-years from Earth. A radio signal from Wolf 359 is detected by a radio telescope on Earth.

(A) (i) State the speed of the radio waves.
(ii) Calculate the distance, in metres, from Wolf 359 to Earth.

(B) another telescope is used to observe the same star in the visible part of the spectrum.
(i) State a suitable detector of visible light that may be used in this telescope.
(ii) State either the time taken for the visible light from the star to reach Earth is less than, equal to or greater than the time taken for the radio waves from the star to reach Earth.

Answer 1

Part A

(i) The speed of the radio waves is the speed of light, or 300 000 km/s.

(ii) Calculate the distance from Wolf 359 to Earth (in metres). We know that 7.8 light years means that for something travelling at the speed of light it will take 7.8 years 365 days each. To find distance, we multiply time (7.8 years 365 days each 24 hours each 3600 seconds each) by speed.

$$d=7.8\cdot365\cdot24\cdot3600\cdot3\cdot10^8=7.38\cdot10^{16}\text{ m}$$

Part B

(i) Charge coupled devices, or CCDs.

(ii) The time is equal because both visible light and radio waves propagate at the speed of light.