3 Things to Know About the Summer Solstice
- Today is the longest day and shortest night of the year in the Northern Hemisphere.
- The solstice occurs because Earth’s tilt toward the sun reaches its maximum angle.
- The hottest days of summer usually arrive weeks later due to seasonal lag, not on the solstice itself.
Today marks the official start of summer in the Northern Hemisphere as we celebrate the summer solstice — the longest day and shortest night of the year.
The solstice occurs when Earth’s 23.5-degree tilt toward the sun reaches its maximum angle. At that moment, the sun appears at its highest point in the sky for locations north of the Tropic of Cancer, creating the most daylight of any day of the year.
The word “solstice” comes from the Latin words sol (sun) and stitium (standing still). If you’ve ever noticed that sunrise and sunset times seem to change very little around late June, that’s because the sun’s position appears to pause before slowly beginning its journey southward again.
What Happens During the Summer Solstice?
During the solstice, the sun is directly overhead at noon along the Tropic of Cancer, located at 23.5 degrees north latitude. This imaginary line circles the globe through parts of Mexico, the Bahamas, Egypt, Saudi Arabia, India and southern China.
For Wisconsin and the rest of the Northern Hemisphere, the result is the longest stretch of daylight of the year. While the exact daylight length varies by location, most of Wisconsin enjoys more than 15 hours of sunshine around the solstice.
After today, daylight hours will slowly begin to decrease. The change is subtle at first — only a few seconds per day — but it accelerates as we move toward autumn.
Why Isn’t the Longest Day the Hottest Day?
One of the most common weather questions this time of year is why the warmest days of summer don’t occur on the solstice.
The answer is something meteorologists call seasonal lag.
Even though daylight begins decreasing after the solstice, Earth continues to absorb more energy than it loses for several weeks. The land, lakes and atmosphere gradually warm throughout late June and July, allowing average temperatures to keep rising.
Across much of the Midwest, the hottest part of summer typically arrives in mid to late July, several weeks after the longest day of the year.
Think of it like preheating an oven. The heating element may be at full power, but it takes time for the oven itself to reach its highest temperature.
Seasons Are Caused by Earth’s Tilt — Not Distance From the Sun
Many people assume summer occurs because Earth is closer to the sun.
In reality, the opposite is true.
Earth actually reaches its farthest point from the sun, known as aphelion, during early July. The closest point, called perihelion, occurs in early January.
The difference in distance is relatively small and has little impact on seasonal temperatures.
Instead, Earth’s seasons are driven almost entirely by the planet’s 23.5-degree axial tilt. During summer, the Northern Hemisphere is tilted toward the sun, resulting in higher sun angles and longer daylight hours. During winter, it is tilted away from the sun, producing lower sun angles and shorter days.
What’s Next?
The next major milestone in Earth’s yearly journey around the sun will be the autumnal equinox in late September. On that day, nearly every location on Earth experiences roughly equal amounts of daylight and darkness.
Until then, summer is officially underway.
So if you’ve been waiting for the season of backyard barbecues, lake days and warm evenings, today’s solstice is nature’s way of saying summer has arrived.
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