Ostara Sabbat rolls around as the sun enters the sign of Aries, between March 20-22, and initiates the season of spring. Ostara is the Spring Equinox, the liminal time, or the gateway time holding in the balance the ending of Winter and the birth of Spring. This is a low ebb in the flow of energy on The Wheel of the Year, and so is considered a quarter, or lesser sabbat.
Our Pantheons Way, an Arlington, Texas Pagan Blog. http://OurPantheons.Org