Because Spring has officially arrived, this week's Topic In Depth focuses on events that occur with the arrival of the new season. Offered by the Howard Hughes Medical Institute, the first Web site (1) focuses on seasonal events like hibernation and migration, and the rhythms behind them. Next is a phenology site (2), where visitors can register to record their observations of Spring online or...

Depending on where you are, spring is either wrapping up or just around the bend. From the sounds of spring peepers peeping to birds chirping, this is definitely the season of re-birth. Check out this handful of sites that look at some of the signs of spring. The first site (1), from naturesound.com, allows you to hear the chorus of a truly spring sound: spring peepers. Next, from Education...

This Topic in Depth explores the Web's offering related to the science of the spring season. The first site -- Seasons, Equinoxes, Solstices, and Climate (1) -- is offered by Assistant Professor of Physics and Astronomy, Eric G. Blackman of the University of Rochester. Visitors can learn how the earth's axis and orbit causes the seasons and what the equinox and solstice are, as well as about...