Start of the Summer Season

Bill’s Blog

Posted: Jun 20, 2020 / 09:15 AM EDT Updated: Jun 20, 2020 / 01:03 PM EDT

Today (Sat. 6/20) is the start of astronomical summer, called the Summer Solstice. The official time for the start of summer is 5:44 pm EDT. Today the sun is as far north as it gets during it’s yearly journey, directly overhead at solar noon over a line we call the Tropic of Cancer, which is just south of Florida.

Here’s a picture of the exact location of the Tropic of Cancer along a Federal Highway in Mexico from 2005 to 2010, the only place I know of where it is annual marked with such precision:

Pic. of Tropic of Cancer in Mexico – from Wikipedia

The Tropic of Cancer’s position is not fixed, but constantly changes because of a slight wobble in the Earth’s axial tilt, the longitudinal alignment relative to the ecliptic, which is the plane in which the Earth orbits around the Sun (see Milankovitch Cycles). The Earth’s axial tilt varies over a 41,000-year period from 22.1 to 24.5 degrees north of the Equator and currently resides at about 23.4 degrees. This wobble means that the Tropic of Cancer is currently drifting southward at a rate of almost half an arcsecond (0.468″) of latitude, or about 15 meters, per year (it was at exactly 23° 27′N in 1917 and will be at 23° 26’N in 2045). Not that you’d notice the difference in a lifetime.

Meteorological summer is the months of June, July and August, so it starts on June 1. The warmest 3 months of the year in West Michigan are June 5 to September 5.

Also, did you know that the seasons don’t have the same length – summer is the longest season in the Northern Hemisphere and winter is the longest season in the Southern Hemisphere. The earth travels around the sun at approximately 67,000 mph. That’s how fast you are moving. You don’t notice because everything else is moving at the same, relatively constant speed. The orbit takes the Earth farther away in summer, so the Earth slows down a bit. When it is closest to the sun (in the first week of January, the Earth is going slightly faster. Think about it…July and August both have 31 days, while February has only 28 (29 in a leap year). If that was reversed (the Earth closest to the sun in July), we’d be 3 degrees hotter in July and 3 degrees colder in January. I’ll vote to keep it the way it is!

Seasons – Graphic from NASA

The earth’s orbit around the sun is not a perfect circle, it’s an ellipse or oval. In the Northern Hemisphere winter, the sun is closer to the Earth than in the summer by about 3 million miles. OK, so you may ask why we get cold in the winter if we’re closer to the sun. Well, that’s because of two things…first, the low angle of the sun’s rays in winter and second, because of the shorter length of day. On the Winter Solstice, we have 9 hours and 1 minutes of daylight in Grand Rapids. On the Summer Solstice (today) we have 15 hours and 21 minutes of daylight. On the Winter Stolstice, the sun climbs to only 23 degrees above the southern horizon at solar noon. Today, the sun climbs to 70 degrees above the southern horizon at solar noon. The sun is higher in the sky today at 7 pm than it is at solar noon on the Winter Solstice in December.

Live cam this AM from Utquagvik, Alaska

This is a live camera shot this morning at Utquagvik, Alaska (aka Barrow, Alaska). This is the northernmost town in the United States, north of the Arctic Circle, where there is 24 hours of daylight today. In fact, the sun will stay above the horizon at Utquagvik until August 1. This morning, when I checked, Utquagvik was reporting a temperature of 33°, light fog and a wind chill of 24°. The average temperature here at Utquagvik this month of June has been 35.4° and they have still not reached 50°. The first 40-degree temperature of the season was on June 11. The last time they were warmer than 50 degrees was September 11. Last August the warmest temperature was 52°. They did have one “warm” day last summer on June 20. The temperature reached 73 on June 20 after an unusual climb of 40 degrees from an early morning low temperature of 32°. So, if you don’t like hot weather, Utquagvik is the place to be.