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Firstly we can measure the distance to the moon by watching exactly where the moon travels through the sky against the background of the stars (parallax) from different spots on the earth's surface t. We can also do this for the distance to the planets. Sending out spacecraft now allows us to measure the size of our solar system and notably the earth's orbit very precisely (down to a few feet!)by measuring round trip transit times of signals.
You can use triangulation / parallax from two separated points on the Earth's surface. (Just like a huge rangefinder)
Stellar parallax is most often measured using annual parallax, defined as the difference in position of a star as seen from the Earth and Sun, i. e. the angle subtended at a star by the mean radius of the Earth's orbit around the Sun. The parsec (3.26 light-years) is defined as the distance for which the annual parallax is 1 arcsecond. Annual parallax is normally measured by observing the position of a star at different times of the year as the Earth moves through its orbit. Measurement of annual parallax was the first reliable way to determine the distances to the closest stars.
Re:Stellar parallax...recording a star's position at different times of year gives a longer baseline and consequently a more accurate measurement of the star's distance,i.e. taking measurements at different points in the Earth's orbit around the sun rather than different points on the Earth's surface.