Google created a Doodle to celebrate the vernal equinox on March 20th. What is the vernal equinox? The first day of spring! Although meteorologists already had their first day of spring based on the temperature, March 20th is the astronomical spring in the Northern Hemisphere. The vernal equinox, also known as March or spring equinox, marks the moment the Sun crosses the celestial equator, which is the imaginary line above the Earth’s equator. At this moment, the Earth’s axis is neither tilted away nor toward the sun, which only happens on the equinox. Every other day, the Earth is tilted at an angle in relation to its orbit around the Sun.