India, Sept. 22 -- Fall is here, at least on the calendar, even though the weather still feels like summer in a lot of places. The autumn equinox is what scientists point to as the true start of the fall season. This year, the first day of fall lands on Monday, September 22, at 2:19 p.m. Eastern for the Northern Hemisphere as per NBC. That is when day and night line up to be almost equal across the globe, about 12 hours each. It is a shift that people have tracked for centuries as the sign that summer is ending.

For meteorologists, though, fall already started earlier. They count the seasons by temperature cycles, not by the sun's path. So for them, autumn began on September 1. That is why you may hear reports calling it fall long before...