The discovery of precession is attributed to Hipparchus around BC. Ptolemy quotes from Hipparchus' now lost work entitled "On the Displacement of the Solstitial and Equinoctial Points" in the seventh book of his 2nd century astronomical text, Almagest , where he describes the phenomenon of precession and estimates its value. The principle of the vernal point acting as the first degree of the zodiac for Greek astronomers is also described in the 1st century BC astronomical text of Geminus of Rhodes.
Geminus explains that Greek astronomers of his era associate the first degrees of the zodiac signs with the two solstices and the two equinoxes, in contrast to the older Chaldean Babylonian system, which placed these points within the zodiac signs. Ptolemy also demonstrates that the principle of the tropical zodiac was well known to his predecessors within his astrological text, the Tetrabiblos , where he explains why it would be an error to associate the regularly spaced signs of the seasonally aligned zodiac with the irregular boundaries of the visible constellations:.
These events can be useful, for example, to estimate the cross-sectional dimensions of a minor planet , or check a star for a close companion. The Sun's placement upon the vernal equinox, which occurs annually around 21 March, defines the starting point for measurement, the first degree of which is historically known as the " first point of Aries ". Zodiac signs have never been used to determine the boundaries of astronomical constellations that lie in the vicinity of the zodiac, which are, and always have been, irregular in their size and shape.
The use of the zodiac as a means to determine astronomical measurement remained the main method for defining celestial positions by Western astronomers until the Renaissance, at which time preference moved to the equatorial coordinate system , which measures astronomical positions by right ascension and declination rather than the ecliptic-based definitions of celestial longitude and celestial latitude.
The word "zodiac" is also used in reference to the zodiacal cloud of dust grains that move among the planets, and the zodiacal light that originates from their scattering of sunlight.
In Unicode, the symbols of zodiac signs are encoded in block "Miscellaneous Symbols": . From Wikipedia, the free encyclopedia. This is the latest accepted revision , reviewed on 5 October For the East Asian zodiac based on the Jovian orbital cycle, see Chinese zodiac.
November 20 Zodiac Sign
For other uses, see zodiac disambiguation. Further information: Former constellations. Further information: Babylonian star catalogues and MUL. Main article: Astrological sign. Further information: Axial precession , Epoch astronomy , Sidereal and tropical astrology , Astrological age , and Ayanamsa. Astronomical symbols Chinese zodiac Circle of stars Cusp astrology Elements of the zodiac. Oxford Dictionaries.
Oxford University Press. Retrieved 19 September The Signs of the Zodiac. Wilcox, London, p.
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See also Lankford, John; Rothenberg, Marc History of Astronomy: An Encyclopedia. The Almagest. Translated and annotated by G. Toomer ; with a foreword by Owen Gingerich. The introduction of the uniform zodiac", Archive for History of Exact Sciences , 64 6 : —, doi : The Mesopotamian traditions. Astronomical Data Service.
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Page Lennart Geminos's Introduction to the Phenomena. Princeton University Press. Ptolemy's Tetrabiblos. Astrology Classics. Project Hindsight.
Retrieved 4 July Hinduism: An Alphabetical Guide. Penguin Books India. London: Board of Longitude, Patrick Grim ed. Philosophy of science and the occult. Ptolemy's Catalogue of Stars: a revision of the Almagest. Carnegie Institution of Washington, Catesby Taliaferro ed. Ptolemy refers to the constellation as Septentarius "the serpent holder". October The Observatory.
The future of person who born on 20 January will depend on your geeky personality. Do You Have Good Karma? Try The Karma Quiz Now!! You understand people and what makes them tick since you had to work harder than other children did to fit in with them.
Scorpio Personality: October 23 - November 21 | HowStuffWorks
With age, Aquarians have learned to rise above certain situations. Now, as an adult, people come to you when they want advice. You never meet a stranger. Unfortunately, it is difficult for you to form many close love relationships. Maybe it is your way of purposely maintaining an emotional distance. Alternatively, is it that you expect people to be like you, disconnected and autonomous? January 20 horoscope predicts that when you get into friendships, they want them to last. Some become like an extended family. The younger people in your life look up to you because you are open-minded about life.
You are strict when it comes to discipline, but it is only to motivate and create a productive human being. They respect that, and so do your parents. What Color Matches Your Personality? Try The Quiz Now!! According to astrology by birthday, Aquarius born today like to keep matters as simple as possible. There is a bit of rebellion in the Aquarius regarding freeing themselves from societal conditioning. Your opinion is that you only live once so live for yourself, be yourself and the rest will follow.
Test Now! Aquarius with January 20 birthday needs space.
You value your freedom. Without that, you can lose touch with what you aspire to be.
Zodiac Signs: Know All About Your Sun Signs
You will have severe goals to meet. You know how you want to live and you want to live well. You are optimistic but can be stubborn about certain things. However in , it was revealed that the stars have shifted so our zodiac signs have changed too. Astrologers around the world celebrate their love of the stars on March 20 which is considered the start of the astrological year.
Sharing both our common and diverse perspectives on how we relate to the stars is the gift of International Astrology Day. Sign in.