Why does your zodiac sign change

This line rotates as the Earth orbits the sun and points to the different constellations; the dozen closest constellations to the sun are considered to be a part of the zodiac. Initially, there were 13 signs, but the Babylonians decided to leave one out, the better to reflect their month calendar. The basic premise of astrology is that your sign corresponds with the constellation the sun passes through on your date of birth.

So someone born on Aug. Scientists, in other words, did not recalculate the zodiac or add a new sign on a whim. NASA just did the math. Well, astrology, on the surface, may be based on the position of the sun relative to certain constellations — and it may be influenced by the movements of the sun, moon, planets and stars, too.

Despite this, there are many people who put great stock in what their horoscope says each morning. They carefully scan the pages of their morning newspaper, searching for their own zodiac sign, and drink in everything that the astrologer has written for them that day.

Even after the thoroughly unpredictable events of the last 12 months! As reported on 24 July Even those of us who dismiss astrology as a load of absolute nonsense know which star sign we are. Or have we? NASA — as in, yes, actual NASA — have confirmed that the sky today is completely different to how it was almost 3, years ago , when the Babylonians first invented the 12 signs of the zodiac.

However, astrologers have a word of warning to all those frantically casting the old zodiac aside. Eastern astrology sidereal reads the planets against the current view of the constellations.

Western astrology tropical sticks with the unchanging positions and accounts for the apparent shift via the great ages around 2, years in each sign. Earth actually travels through 13 signs, including Capricorn, Aries, and, yes, Ophiuchus, but some 3, years ago the Babylonians—not NASA—decided 12 was neater than 13, so excluded the 13th zodiac sign and divided the zodiac into 12 parts based on the 12 months of their calendar, according to NASA.

To make a tidy match with their month calendar, the Babylonians ignored the fact that the sun actually moves through 13 constellations, not That post was originally written in , but as the story of a shifting zodiac circulates once again, NASA has retweeted it again.

While the Tumblr post it linked too is fairly straight forward, the staid space agency gets a little spicier in its take on astronomy on its early education site. Many ancient people believed that a person's behavior, emotions, and fate were heavily influenced by the time of that person's birth i. The zodiac constellations, as envisioned by ancient astronomers, were ascribed specific patterns that resemble the shapes of animals and human beings.

The constellations of the zodiac actually form an imaginary belt in the sky that extends about eight degrees above and below the ecliptic plane as is shown. As we look at the position of the zodiac constellations at any given time of the year, the Sun is between the Earth and one of these constellations, as Figure 3 shows.

Vernal and autumnal equinoxes. We are familiar with the Earth's equator because of our knowledge of geography. If we could extend the earth's equator into space so that it could be viewed against the background of stars, we would be able to see what in astronomy is called the celestial equator. Because the Earth's axis of rotation is tilted with respect to the ecliptic by The two points in the sky where these two planes cross are called the equinoxes.

We call the vernal equinox the intersection point where the Sun, in its apparent motion against the background stars along the ecliptic, crosses the celestial equator from south to north, usually occurring around March 21 st. Similarly, we call the autumnal equinox the intersection point where the Sun, in its apparent motion against the background stars along the ecliptic, crosses the celestial equator from north to south, usually occurring around September 21 st.

The first day of Spring then corresponds to the vernal equinox and the first day of Fall corresponds to the autumnal equinox. During the time of the equinoxes, we on the Earth experience twelve hours of day and twelve hours of night.

The precession of the equinox. Figure 4 The precession of the Earth around its axis. The Earth's rotation on its axis has caused the Earth's shape to diverge from a sphere, and has caused the Earth's equatorial regions to bulge out. Because the Earth's equator is tilted with respect to the orbital plane of the Earth around the Sun, the Earth's equatorial bulge is also tilted with respect to the plane along which the Sun and Moon travel.

The Moon and the Sun exert a gravitational drag on the Earth's equatorial bulge, trying to pull the Earth's equatorial region to be aligned with the ecliptic plane. This pull, along with the rotational motion of the Earth on its axis, the revolution of the Earth around the Sun, and the revolution of the Moon about the Earth, cause the Earth to wobble about its axis of rotation, similar to the motion of a spinning top. This motion is called precession. It is the wobbling of the equatorial plane that causes the line of the intersection of the equatorial and ecliptic planes to move.