Fall is officially underway with the autumnal equinox happening last night. This equinox occurred at approximately 9:30 p.m. last night and marks the days getting shorter in the Northern Hemisphere. Due to the Earth’s tilted axis the two hemispheres trade seasons throughout the year. The equinox marks one of the two days of the year when day and night are closest to equal in length. The vernal equinox occurs in March.