AST 104 Lecture Notes - Lecture 6: Angular Diameter, Minute And Second Of Arc, Optical Illusion
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The angular size you observe depends on the physical size of an object and on its distance from you. 1 arcminute = 1 arcmin = 1/60 degree. 1 arcsecond = 1 arcsec = 1/60 arcmin = 1/3600 degree. Turn it around and measure the distance to a star using the diameter of. Earth"s orbit and the change in angle to the star! As the earth orbits the sun, our line of sight to a star changes. For the nearest stars, there is a tiny but measurable change. Compare the star"s apparent position to the very distant stars behind. The apparent shift in the direction of an object as a result of the motion of the observer is called parallax. Parallax is an optical illusion that lets us measure distances. Think triangulation. it"s one method for surveying distances. This is actually familiar, and part of how our brains gauge distance. Try looking at a scene through one eye, then another.
