Distance2 - Distances-Trigonometric Parallax Unlike the...

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Distances---Trigonometric Parallax Unlike the other sciences, astronomy is entirely observational. You cannot run experiments on things. You cannot manipulate the objects to see how they work. In order to compare the objects you see from the Earth, you must first know how far away they are. Obviously, you cannot use a tape measure or send spacecraft out to the stars and measure how far they travelled. Bouncing radar off the surfaces of stars would not work because: (1) stars are glowing balls of hot gas and have no solid surface to reflect the radar beam back and (2) the radar signal would take years to just reach the nearest stars. A favorite way to measure great distances is a technique used for thousands of years: look at something from two different vantage points and determine its distance using trigonometry. The object appears to shift positions compared to the far off background when you look at it from two different vantage points. The angular shift, called the parallax, is one angle of a triangle and the
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