![]() What sort of coordinate system can we use on our imaginary celestial sphere? An easy starting point might be u "The Prime Meridian" by chrismetcalf is licensed under CC BY-NC-SA 2.0 "File:Orion (constellation) Art.svg" by Sanu N is licensed under CC BY-SA 4.0 For example, if you want to study the Crab Nebula, it helps to know that it is in the constellation Cancer. In the modern terminology, the constellations represent 88 defined regions in the sky that are often used to help us find objects we want to study. Today, astronomers still use constellations, but define them a little differently. Often, they told stories about the characters the constellations represented. They gave the constellations various names based on mythic heroes and beasts of legend. Ancient people put stars into groupings they called constellations (Greek for “stars together”). There are no continents in the sky, but there are groups of stars that appear to belong together. But before we examine our stellar coordinate system, let’s ask ourselves, are there any short cuts we can use to help us find objects in the sky? If we were looking for New York City on a globe, we might have start at the equator or prime meridian if we know that New York is on the continent of North America. "File:Latitude and Longitude of the Earth.svg" by Djexplo is licensed under CC0 1.0įor our celestial sphere model, we need a similar set of coordinates, but one that is placed on the inside of our sphere. On the other hand, longitude is measured in terms of degrees east or west of the prime meridian, an imaginary line that passes through Greenwich, England. Latitude is measured in terms of degrees north or south of the equator. As with any coordinate system, we need to define a few points of reference from which we can measure our relative position. On Earth, we use the system of latitude and longitude to mark a position on the surface of the planet. After all, we cannot study an object if we cannot find it. ![]() "WTF?" by BillKasman is licensed under CC0 1.0 Įven though there is no real celestial sphere with stars embedded on its inner surface, the celestial is still a useful model for a coordinate system to locate stars and planets that we want to study. Objects that are really far apart can appear close together if they are along the same line of sight. Think of an optical illusion that makes two objects look close together even when they are in fact, far apart. They only appear to be close together because they happen to be in roughly the same line of sight from our vantage point. Stars that appear to be close together in the sky may in fact be hundreds or thousands of light-years away when we consider them in three dimensions. In fact, they are not all equidistant from us. Of course, today we know there is not physical celestial sphere and that the stars are much further away from us than ancient thought. They considered this celestial sphere to be a real, physical structure and all the stars were more or less the same distance from Earth. Some people saw the Firmament as a literal dome or sphere where the stars hung. Somewhere beyond Saturn, was the Firmament or Vault or Heaven where the stars resided. The Sun, the Moon, and the five known planets all revolved around the world. Being the center of all creation made Earth a special place. They saw the Earth as the center of all things. ![]() ![]() ![]() Indeed, that is how most people throughout human history thought things were. Looking up at the sky and watching the Sun, the Moon, and the stars go by, it’s easy to think that we are at the center of the universe, that everything revolves around our little world. \)Ĭelestial Sphere - Earth Stars.png by ChristianReady is licensed under CC BY-SA 4.0 ![]()
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