Summer is ending, and fall is right around the corner. While the official start of fall is over three weeks away, Meteorological fall starts on September 1st. So, what is the difference between the two?

What is the difference between Meteorological Fall and Astronomical Fall?

Meteorological fall is based on the annual temperature cycle and the calendar.

Meteorologists and climatologists break the seasons down into groupings of three months to better reflect temperature trends. For example, Meteorological Fall includes the months of September, October and November. Breaking down the seasons into groupings of three months makes it easier to keep weather and climate records.

Astronomical fall is based on the position of the Earth in relation to the sun.

Astronomical fall begins on the vernal equinox. The vernal equinox is when the sun passes over the equator. Astronomical fall starts on Sept. 22 this year and will last until the winter solstice on Dec. 21. The start and the length of astronomical fall varies each year. According to the National Centers for Environmental Information (NCEI), astronomical seasons last between 89 and 93 days due to the elliptical shape of the Earth’s orbit around the sun.

Whether you’re talking about meteorological fall or astronomical fall, both mean that the days are getting shorter, temperatures are getting cooler and leaves will soon change colors.