How are the zodiac constellations used today? No evidence has been found for the predictive power of astrological predictions based on the zodiac, as demonstrated in this 1985 paper from the journal Nature (opens in new tab). Now, however, astrology is commonly considered a pseudoscience. In fact, the famous astronomer Johannes Kepler (opens in new tab) was considered an astrologer during his life in the 1600s, according to Time magazine (opens in new tab). They referred to "The Twins," "The Lion" and "The Crab" thousands of years ago, which are the same constellations we (and the ancient Greeks) know as Gemini, Leo and Cancer, respectively.Īstrology was once considered part of the science of astronomy. According to a 2017 paper from the journal of the American Philosophical Society (opens in new tab), many of the Greek constellations that we consider to be the Western zodiac today were adopted from Babylonian astronomers. Ancient China, Sumeria in the Middle East and Egypt each had their own star maps, for example. However, people were mapping the sky long before these names took hold. According to Encyclopedia Britannica (opens in new tab), that is thanks in part to the Almagest, an influential catalog of stars and constellations created by the ancient mathematician Claudius Ptolemy in the second century. Most of the constellations in the Northern Hemisphere's skies bear Greek and Roman names. History of the western zodiacĪ 16th century engraving of Claudius Ptolemy, mathematician and astronomer who created a geocentric model of the solar system and wrote the Almagest, one of the most influential scientific texts in history. Just 12 of those constellations make up the western zodiac. The path of the ecliptic passes through 13 of the 88 constellations officially recognized by the International Astronomical Union (opens in new tab) (IAU) since 1929. Those constellations are defined mostly by their position on the ecliptic (opens in new tab), an imaginary or projected line in the sky that marks the perceived path of the sun (as well as the rough paths of the planets and the moon, which are all more or less on the same plane) over the course of a year on Earth. Orion isn't one of the zodiac constellations, though. But from our viewpoint on Earth, they look like nearby neighbors. But the farthest star in that constellation is Alnilam, which is about 1,300 light-years away. But stars that seem to be right next to each other in a constellation may in fact be hundreds of light-years apart (opens in new tab).įor example, in the well-known constellation Orion (opens in new tab), the nearest star to us is Bellatrix, a bit more than 200 light-years from Earth. Read more: Space junk is blocking our view of the stars (opens in new tab)Īlthough we're looking at stars across vast expanses of three-dimensional space, the arrangement we see looks two-dimensional. Similar to how our sun (opens in new tab) looks like it's moving across the sky when it's really our planet rotating as it orbits the sun, constellations appear to be rotating across the sky when that movement is really due to our changing viewpoint. That appearance of star movement actually has more to do with the rotation of Earth (opens in new tab) than the movements of stars themselves. (Image credit: Till Credner) (opens in new tab)įrom Earth, stars appear to move across the sky on a regular schedule. Read more: How the constellations got their names (opens in new tab) What is a constellation?Ī visual mosaic of the 12 classic constellations in the western zodiac, photographed in the night sky, marked and outlined. The sign of Pisces, for instance, currently corresponds to the rise of the constellation of Aquarius. Today, the astrological signs differ from these constellations, bearing only a loose reference (opens in new tab) to one another. (The 13th, Ophiuchus (opens in new tab), it omitted because when the signs were first described, the stars were not in exactly the same position as they are today.) The 13 constellations in the path of the ecliptic are:Īstrologers use 12 of these constellations to roughly correspond with the signs of the zodiac to make predictions. As Earth rotates (opens in new tab), the sun, moon and planets seem to move generally along a set path through the sky, called the ecliptic (opens in new tab).
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