Precession has also had the effect of shifting the equinoxes of Earth - the two points of the year at which day and night have equal lengths - along the ecliptic. Over the last 2,500 years, the intersection of the celestial equator and the ecliptic has drifted west along the ecliptic by 36 degrees - about one-tenth of its length.Īn illustration showing Earth's wobble along its rotational axis. This means that the North Pole isn't always pointing in the same direction as the background stars of the celestial sphere, and this effect accumulates. Watching this pole over the course of 25,800 years, we would see it trace out a circle over the Earth. To picture this precession, imagine a literal pole extending out of Earth at the North Pole. Known as precession this 'wobble' has a 25,800-year cycle. The gravity of the moon and the sun, and to a lesser extent the planets, acts on Earth's equatorial bulge - caused by the planet's rotation - to shift its axis of rotation. The cause of the shifting in zodiac signs is precession, the slight 'wobble' Earth experiences as it orbits the sun. The problem was, that these ancient astrologers weren't aware of a ' wobble' in Earth's motion that would seriously disrupt their system as time progressed. The other astrological signs of the zodiac were categorized in a similar way, each grabbing its own 30-degree slice of the ecliptic. This intersection is also known as the vernal equinox and the spring equinox in the Northern Hemisphere because it is considered the first day of spring.Ģ,200 years ago this zero point occurred in Aries, hence its name the "first point of Aries." As a result, Aries the constellation occupied the first 30 degrees of the ecliptic from 30 to 60 degrees was taken by Taurus, and Gemini was positioned from 60 to 90 degrees. The zodiac was initially developed around 600 BCE and its zero point was defined as the point that the ecliptic intersected with the celestial equator - the great circle of the terrestrial equator on the celestial sphere. (Image credit: Wikimedia commons/Tauʻolunga) An illustration of the sun's motion relative to Earth throughout the year as it crosses in front of constellations representing the astrological signs of the zodiac.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |