posted by Sara .
I know what a baseline is, but what baseline is used in astronomy? y do we need vary the length of baselines we use?
Is the baseline the diameter of the earth's orbit?
I really do not get the 2nd part.
The baseline IS the diameter of the Earth's orbit for parallax measurements. That s a way of measuring the distance of "closes" stars against a more distant star background.
There are other types of radio telescope and optical interferometric measurements in which the observations are made from telescopes that are hundreds to milliions of meters apart, simultaneously. Such measurements are capable of providing images of very high optical resolution.