When Does Summer Begin?

Most people consider the first day of summer to be the summer solstice, which rang in at 11:32 p.m. EDT on June 20 this year. This is because, astronomically, the sun was directly overhead of the Tropic of Cancer at that time.

As the Earth rotates around the Sun, at different times of the year the Sun will be situated directly overhead at midday. The day the sun is straight up at noon over the Tropic of Cancer and Capricorn (23.5 degrees N and S latitude) are the summer and winter solstices, respectively.

The Autumnal (Fall) Equinox is the day the Sun is again highest in the sky at noon over the equator as the apex progresses south. Many refer to astronomical summer on June 20th or 21st, as the first "official" day of summer.

Most meteorologists will argue that summer has been well under way by then and they have been enjoying at least three weeks -- if not longer -- of "summer" already. Meteorologists observe seasons over different time periods. Meteorological summer begins on June 1, fall begins September 1 and winter begins December 1. There are a couple of very important reasons why this is the case. The most important is for climate record-keeping. Climatologists require set time periods to calculate averages and do seasonal comparisons over the years. Astronomical dates will fall on different days depending on the year and keeping seasonal climate records based on those dates would be confusing and inaccurate.

A second reason is that weather-wise, it makes more sense around the globe. For example, much of the northern hemisphere is entrenched in summer weather by June 1 and winter weather on December 1. In fall, the heat of the summer is waning by September 1 and by March 1, spring, mild surges of air from the south are becoming a regular occurrence and the seasonal severe weather threats grows.

Image: A field of sunflowers near Vineuil in the Loire Valley, France (Wikimedia)