Inside Story

The sunniest time of the year is here. Solar Summer – one of the lesser-known versions of the season – has arrived in the Northern Hemisphere.

As AccuWeather reports, there are many ways to quantify the season. Memorial Day weekend signals the start of summer for beachgoers and vacationers across the United States. Weather forecasters declare June 1 as the beginning of meteorological summer, while others wait until the June solstice to welcome the arrival of astronomical summer. So, what are the major differences between the three?

Solar Summer

May, June and July are the months when the Northern Hemisphere receives the most sunlight due to the Earth’s tilt on its axis. Because of this, the three-month period is known as solar summer.

Despite the Northern Hemisphere receiving more sunlight from May through July than any other months of the year, it is usually not the hottest three-month span. This is due to a lag between when the Northern Hemisphere receives the most amount of sunlight and when the atmosphere is at its warmest point of the year.

Astronomical Summer

According to the National Oceanic and Atmospheric Administration (NOAA), people have used observable periodic natural phenomena to mark time for thousands of years. The natural rotation of Earth around the sun forms the basis for the astronomical calendar, in which we define seasons with two solstices and two equinoxes. Earth’s tilt and the sun’s alignment over the equator determine both the solstices and equinoxes.

The equinoxes mark the times when the sun passes directly above the equator. In the Northern Hemisphere, the summer solstice falls on or around June 21, the winter solstice on or around December 22, the vernal or spring equinox on or around March 21, and the autumnal equinox on or around September 22. These seasons are reversed but begin on the same dates in the Southern Hemisphere.

Because Earth actually travels around the sun in 365.24 days, an extra day is needed every fourth year, creating what we know as Leap Year. This also causes the exact date of the solstices and equinoxes to vary. Additionally, the elliptical shape of Earth’s orbit around the sun causes the lengths of the astronomical seasons to vary between 89 and 93 days. These variations in season length and start date would make it very difficult to consistently compare climatological statistics for a particular season from one year to the next. Thus, the meteorological seasons were born.

Meteorological Summer

Meteorological summer, also known as climatological summer, is a period defined by weather patterns and temperature cycles rather than astronomical events like soltices and equinoxes.  It consistently begins on June 1st and lasts through August 31st in the Northern Hemisphere, and December 1st through February 28th (or 29th) in the Southern Hemisphere, according to FOX Weather. 

Meteorological observing and forecasting led to the creation of these seasons, and they are more closely tied to our monthly civil calendar than the astronomical seasons are. The length of the meteorological seasons is also more consistent, ranging from 90 days for winter of a non-leap year to 92 days for spring and summer. By following the civil calendar and having a fixed time frame, it becomes much easier to calculate seasonal statistics from the monthly statistics, both of which are very useful for agriculture, commerce, and a variety of other purposes.

Dog Days of Summer

The “dog days of summer” is yet another way to quantify the season and is the shortest of the bunch, starting on July 3 and ending on Aug. 11. During this 39-day period, Sirius—known as the dog star—is in the same area of the sky as the sun.

In ancient times, it was thought that the added light from Sirius (the brightest star in the night sky) added extra heat to the day. However, the star is nearly 6 trillion miles away from Earth, and its light is too dim to change the temperature on our planet.

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