They are, however, affected by radio noise, i.e., radio and TV broadcasts, cellular phone transmissions, etc. One the major radio observatories in the United State is located in a radio-free zone in Greenbank, West Virginia. Fortunately, parallax was found, for without parallax, we wouldn't know which stars are nearby and which are far away. Thus, if you divide the Moon into 1800 pieces, you'll get 1 arcsecond. Through the trigonometry of the extremely skinny triangle, we can then measure a distance.
Astronomers always try to make things as easy as possible for themselves.
To make things easy, they define a new unit of distance, called the parsec. One parsec is the distance a star would have if it had a parallax angle of 1 arcsecond. Note that by defining a parcsec in this way, the relationship between the measured parallax angle and the implied distance is trivial. If a star has a parallax of 1 arcsec, its distance is 1 parcsec. And so on.