Thursday is the first day of spring, or the vernal equinox, in the Northern Hemisphere. During an equinox, the center of the sun is on the same plane as the equator. After the vernal equinox in March, the Northern Hemisphere tilts toward the sun until the June solstice, when the sun begins to migrate back south.

Spring brings a dramatic change to Washington’s sky this year. The bright planets that have kept us company over the long winter nights are dropping out of sight, and winter’s bright constellations give way to the more subtle stars of the season.

Spring equinox means the first official day of spring is here. Discover the science and traditions of what’s also called the vernal equinox..