Mobile phones put star secrets at risk

1 	Most of us are happy to look at stars using our eyes. Why do astronomers 		'look' at stars using instruments which receive other wavelengths?

2 	Calculate the wavelength of the telecommunication signal described in the 	passage [c = 3x10 8 ms -1 ] .

3 	Why are short wavelengths used?

4 	A satellite dish of diameter 10 m is used to relay this signal. Calculate the 		angle over which this signal will spread.

5 	The satellite is 36000 km above the Earth's surface. Over what area of the 		Earth will this signal spread?