Hot! Summer Solstice 2012

Summer officially kicks off today, with the summer solstice marking the longest day of the year on June 20, at least in the Northern Hemisphere.

This year's summer solstice takes place a day earlier than it's been for the past three years, due to the fact that 2012 is a leap year this February got an extra day, to keep our calendar year of 365 days in sync with the astronomical year, which is about 365.24 days.

In general, the exact timing of the summer solstice changes from year to year, "but there's a bigger jump when you have a leap year," explainedPictures: Summer Solstice Marked With Fire, Magic . )

Highest Sun at High Noon

The solstices are the results of Earth 's north-south axis being tilted 23.4 degrees relative to the ecliptic, the plane of our solar system. This tilt causes different amounts of sunlight to reach different regions of the planet during Earth's year-long orbit around the sun.

Today the North Pole is tipped more toward the sun than on any other day of 2012. (The opposite holds true for the Southern Hemisphere, where today is the As a result of Earth's tilt, the path of the sun across the sky rises in the lead-up to the summer solstice, then begins descending for the rest of the summer.

(See pictures of the sun's path across the sky an entire year in a single frame.)

At high noon on the summer solstice, the sun appears at its highest point in the sky its most directly overhead position in the Northern Hemisphere.

That doesn't mean the sun will be exactly overhead at noon for everyone, said Cornell University astronomer James Bell .

It depends on the viewer's latitude the sun will shine down directly overhead at noon only along the Tropic of Cancer, an imaginary line that circles the planet at about the latitude of Alaska ," Bell explained.

Solstice Is Longest Day of the Year Not Hottest

On the summer solstice, the Northern Hemisphere receives more sunlight than on any other day of the year but that doesn't mean the first day of summer is also the hottest.

(Related story: Earth's oceans and atmosphere act like heat sinks, absorbing and reradiating the sun's rays over time. Even though the planet is absorbing lots of sunlight on the summer solstice, it takes several weeks to release it. As a result, the hottest days of summer usually occur in July or August.