how is the Universe mapped Using radio astronomy?

Answer 1

The universe isn't completely mapped out using radio telescopes because not everything emits radio waves. If you want to learn how it's done take a look here.

Answer 2

The simple answer is that radio telescopes are pointed all over the sky, used to measure the radio flux at each point, and then the data are combined to make a map. All sky surveys at many different radio frequencies do exist and tell us a great deal about the Universe.

If you are wondering how radio telescopes work, then here is a brief description. There are two types of radio telescopes: single-dish telescopes and multi-element arrays.

Single dish telescopes consist of a large metal dish which reflects the radio waves towards a receiver. The receiver contains a small antenna, which works in exactly the same way as the antenna on your cell-phone: the waves cause electrons in the antenna to oscillate, giving an electrical signal which can be measured electronically. Single dish receivers usually contain just one resolution element, meaning that if you want to make a picture you need to point the telescope at many adjacent regions: each pointing gives one "pixel".

Multi-element arrays or Interferometers work by interfering the signals received from multiple telescopes. If you do this for a variety of separations and orientations, you can build up enough information to synthesize an image. The image's "pixels" will be determined by the maximum separation of the telescopes. This may sound confusing, and the reason is that one needs to use advanced calculus to truly appreciate how this works. If you are mathematically inclined, this process is equivalent to a Fourier Transform. For the record, the mathematics involved are quite elegant.