Since mankind's earliest days on Earth, the movement of the Sun across the heavens has garnered our rapt attention. We can measure the Sun's path from two different vantage points: in reference to our own position on the Earth, or in reference to its path across the backdrop of the stars. For many purposes, such as hunting, planting and harvesting and other seasonal events, observing the Sun's passage relative to ones' physical location has been of vital importance. The movement of the Sun (and the other planets) across the field of stars has been valued, on the other hand, for selecting propitious times for both mundane proceedings and spiritual rituals, for navigation, and for predicting astronomical events.
Astrologers also use both methods of reckoning. Western astrologers use the seasonal or Tropical Zodiac, where the signs are based upon the annual movement of the Sun in relationship to the Earth. The Tropical sign of Aries begins at the point in the sky where the Sun crosses the Equator going North on the first day of Spring (for the Northern Hemisphere), around March 21st. Vedic astrologers, on the other hand, use the stellar or Sidereal Zodiac, where the Sidereal sign of Aries is determined by the placement of the stars in the Zodiacal constellations of the night sky. For the 21st century, the Sun enters Sidereal Aries around April 15th.