Today is the Spring or Vernal Equinox with Spring officially beginning at 1:27pm EST (Eastern Standard Time). The Spring Equinox and the Fall Equinox are the two days of the year that day time and night time are of equal duration.
If you were to plot the position of the Sun relative to the backdrop of the stars (an impossible feat since the stars can't be seen in the day) on the Spring Equinox you would observe that the Sun rises is in a slightly different position every year. The Sun actually moves backward through the zodiac at a rate of about 50 seconds per year or 1 degree every 72 years. This is called the Precession of the Equinox and is due to the earth's wobble on its rotation axis.
It takes approximately 2160 years for the Equinox to precede through a sign. Currently, on the Spring Equinox the Sun rises in the constellation of Pisces at 6 degrees and 3 seconds. In about 430 years it will begin to rise in the sign of Aquarius. Prior to the year 270 B.C. it rose in the sign of Aries.
India's system of Vedic astrology has always accounted for the Precession of the Equinox throughout its long 4000+ year old history. The fact that India's astronomers were able to make this infinitesimal calculation is testimony of India's rich heritage of advanced astronomers, mathematicians, and astrologers.