Astronomical dates refer to days on which a celestial event occurs, such as a meteor shower or full moon. Astrological signs, on the other hand, indicate the position of the sun on one's birthday.
Everyone has an astrological sign, such as Cancer or Scorpio. Each person's sign is based on the position of the sun on the day the person was born.
For the purposes of sun signs, the earth's revolution around the sun is divided into 12 equal sections of 30 degrees each. Over the course of the year, the earth passes through each of these sections in turn. Each day that the earth is in a particular section, the sun appears to rise through that section's constellation. This is what determines the zodiac signs. For example, between March 21 and April 19, the sun rises through the Aries section, so anyone born on these days is an Aries.
Astronomical dates are simply a way of organizing celestial events based on the calendar. Astronomical dates include the days on which things such as planetary movements, meteor showers, moon phases, space craft events and eclipses occur. Astronomical dates can span several days, a single day or, in the case of events like an eclipse, only a few hours or minutes.