Which is the first astrological sign in the zodiac?
Aries is the first astrological sign in the zodiac, spanning the first 30 degrees of celestial longitude (0°≤ λ <30°), and originates from the constellation of the same name. Under the tropical zodiac, the Sun transits this sign from approximately March 21 to April 20 each year. This time duration is exactly the first month of the Solar Hijri calendar (Hamal/Farvardin/Wray).
According to the tropical system of astrology, the Sun enters the sign of Aries when it reaches the March equinox, which occurs on average on March 21 (by design). Because the Earth takes approximately 365.24 days to go around the Sun, the precise time of the equinox is not the same each year, and generally will occur about six hours later from one year to the next until reset by a leap year. February 29 of a leap year causes that year's vernal equinox to fall about eighteen hours earlier compared with the previous year. From 1800 to 2050 inclusive the vernal equinox date has (or will) range(d) from March 19 at 22:34 UT1 in 2048 to March 21 at 19:15 UT1 in 1903.
Under the sidereal zodiac, the sun currently transits Aries from April 15 to 14 May (approximately).