Parallax - How Parallax Works, Parallax Measurements
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Astronomers must use very indirect methods to measure the distances to stars and other astronomical objects. Measuring a star's parallax is a way to find its distance. This method takes advantage of the apparent shift in position of a nearby star as it is observed from different positions as the earth orbits the Sun. Because the parallax effect depends upon the earth's motion about the Sun, it is often referred to as the heliocentric parallax.
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To understand how parallax works, hold your thumb in front of your face. Alternately open and close each eye and notice how your thumb appears to move back and forth with respect to the background wall. Now move your thumb closer to your face and notice how this effect increases as the distance between your eyes and thumb decreases. This apparent motion (you did not really move your thumb) is call…
In the sixteenth century, Copernicus proposed that the earth and planets orbited the Sun. At the time one of the arguments proposed against the Copernican view was that there should be a heliocentric parallax if the Sun was indeed the center of the solar system. At the time no such parallaxes had been observed. Copernicus countered rather simply by stating that the stars were much farther away tha…
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