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The summer solstice is an event that has for centuries been helping humankind define — astronomically — when summer starts.
Occurring on either June 20th or June 21st (depending on the year), the summer solstice happens when the sun rises and sets at its northernmost point.
In terms of how long the sun is in the sky, the summer solstice is also the longest day of the year.
Why Does The Summer Solstice Occur?
OK, so now that you know the sun rises and sets at different places along the horizon, you want to understand more about why it does that.
As you might already know, our earth’s axis is at a tilt.
In fact, our earth is actually tilting at around 23.5 degrees.
Because of that, as our earth orbits around the sun, sunrises and sunsets will appear at slightly different places on our horizons each and every day. Sunrises and sunsets always track along our horizons in a steady north-to-south (or south-to-north) pattern.
Reaching The North & Going Back South
At the point, on the summer solstice, that our sun has reached its northernmost point, something happens… The sun begins to rise and set farther south each and every day.
Unless you’re carefully measuring the sunrises and sunsets with special equipment, you’ll probably not notice the day-to-day movement. But it happens.
In September, during the autumn equinox, the sun will appear to rise and set nearly due east and west respectively. (That is, of course, in the middle Northern Hemisphere latitudes where most people reading this article live).
By the winter solstice in December, the sun rises and sets at its southernmost point.
Using The Summer Solstice To Mark The Start Of Summer
While every culture and era does things slightly differently, it’s been the case for a long, long time that the summer solstice is used by many people in the Western Hemisphere as the starting point for summer.
That’s why most calendars list June 20th or June 21st as the start of summer.
In fact, astronomically, there are precise times when the summer solstice occurs. In 2010, that’ll be at 7:28 am Eastern Standard Time in the United States.
…And now you know why the weather people on the news have such a precise time for marking the start of summer every year!
I'm a weather geek from Florida who's been studying meteorology and watching weather patterns for years! I enjoy sharing little-known facts and fun stuff about the weather. I especially like sharing interesting details about weather events and conditions that can affect you… and how to prepare for Mother Nature's ever-changing weather patterns.