We are in the literal infancy of such discovery. Our ability to "see" these great distances and calculate how far away the most distant objects are rely upon our understanding of the red shift and the accuracy of the instruments we using in measuring these distances. That means by default the original expansion of the universe happened at a speed far greater than the speed of light to go from zero to 31 billion light years in size in a matter of seconds.īut could there be more galaxies beyond the 45 billion light years we know of? Yes! That should mean that we cannot see anything more than 13.8 billion light years away.Īstro-physicists have explained this with the theory that in the first few seconds of its existence, the universe expanded to about one half the size it is today. This 45 billion light years away is in all directions possible from our galaxy.īut you have to consider that we live in a universe that is approximately 13.8 billion years old and accept the fact that nothing can travel faster than the speed of light. ![]() ![]() Problematic to that is the fact that they are moving away from us and that motion is accelerating. The most distant reaches of the visible universe, the known universe, sit some 45 billion light years away. That's about #10,000# times the angular size as Pluto, meaning that we can see much more detail. NGC 1300 is a spiral galaxy #23.7 " million light years"# away, which has an angular size of #1116 " arc-seconds"#. Which is about #22# pixels across for Hubble. Comparing that with Pluto's diameter of #2372 " km"# tells us that Pluto's largest angular size is At its closest, Pluto is #4.28 " billion km"#. The closer it is to the Earth, the larger it appears. Pluto's angular size changes as it orbits the sun. To put this in perspective, the entire sky is a #360^o# field of view, or #1,296,000 " arc-seconds"#. We measure resolution in arc seconds because it tells us how much of our view of the sky an object takes up. A single arc-second is #1"/"3600#th of a degree. That means that each of these pixels is #.05 " arc-seconds"# wide. ![]() If we look at a Hubble image of Pluto from 1996, we can see these pixels.Ĭurrently, Hubble's resolution is about #.05 " arc-seconds"#. These "bins" correspond to pixels in the resulting image. These cameras use a grid of "bins" which collect and count photons. Hubble uses a special type of camera called a CCD, or charged couple device. While researching this answer, I came across this article which provides a more in depth answer to the question. #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. 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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