I've read of people doing 108 Sun Salutations (Surya Namaskar A) at the time of the spring equinox. What is the significance of the number 108?
The number's significance is open to interpretation. But 108 has long been considered a sacred number in Hinduism and yoga. Traditionally, malas, or garlands of prayer beads, come as a string of 108 beads (plus one for the "guru bead," around which the other 108 beads turn like the planets around the sun). A mala is used for counting as you repeat a mantra—much like the Catholic rosary.
Renowned mathematicians of Vedic culture viewed 108 as a number of the wholeness of existence. This number also connects the Sun, Moon, and Earth: The average distance of the Sun and the Moon to Earth is 108 times their respective diameters. Such phenomena have given rise to many examples of ritual significance.
According to yogic tradition, there are 108 pithas, or sacred sites, throughout India. And there are also 108 Upanishads and 108 marma points, or sacred places of the body.
And, yes, one can offer a yoga mala of 108 Sun Salutations. Please take a moment to visit www.globalmala.org for more information on the power of 108 and joining the "mala around the earth" to be formed by the worldwide yoga community on September 21 and 22 of 2007.