What event occurs on March 21st regarding sunlight exposure?

March 21st is typically recognized as the vernal equinox in the Northern Hemisphere. On this day, the sun is positioned directly above the equator, resulting in nearly equal day and night lengths across the globe. This event marks the transition from winter to spring, leading to an increase in sunlight and energy received by the Earth's surface as the days begin to grow longer.

Gaining insulation refers to the increasing duration and intensity of sunlight that areas in the Northern Hemisphere receive as they move into spring. This phenomenon contributes to warming temperatures, the melting of snow, and the rejuvenation of plant life as they begin to grow after the cold winter months. Therefore, March 21st is associated with the gaining of insulation as the sun's rays start to have a more direct and potent impact on the Earth, leading to these seasonal changes.