#p = (1"AU")/d#, or in other words, #d=(1"AU")/p#Īstronomical units are not the most convenient units to work with, though, so instead we define a parsec to be the distance to a star that shows #1# arc-second of parallax angle. The parallax of an object is its apparent shift in position when it is viewed from twodifferent vantage points.It is commonly used on Earth to measure distances. Since the star will be very far away, we can make the assumption that #tan p# is about equal to #p#. We can use #tan p# to find the distance to that star. In the image above, we can see that by cutting #alpha# in half, we get a right triangle where one leg is the distance between the sun and the other star. This is enough to get a noticeable angle, #alpha#, between the star's two apparent locations. One AU is the average distance from the Sun to the Earth. If we made two observations of the same star on opposite sides of the Earth's orbit, we would have a separation of #2# astronomical units, or AU. In astronomy, the distances to other stars is too great to measure using two objects on the Earth's surface. This is true in astronomy as well, but on a much larger scale. The closer the object is, the more it appears to move relative to the background. If you look with just one eye, then the other, the object will appear to move against the background.īecause your eyes are separated by several centimeters, each eye has a different perspective of where the object is relative to the background. One way to understand parallax is to look at a nearby object and note its position against a wall. Parallax is a method of using two points of observation to measure the distance to an object by observing how it appears to move against a background.
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