Published: 2012-06-20 08:30:00
Updated: 2012-06-20 08:30:40
Posted June 20, 2012
By Tony Rice, NASA Ambassador
The Northern Hemisphere will mark the summer solstice at 7:09 pm EDT Wednesday as the sun reaches the highest point in the sky, directly above the Tropic of Cancer. This is also "the longest day" because the sun rises earlier and sets later than any other day, producing the most hours of sunlight.
Wednesday will have 14 hours, 36 minutes of sunlight, 1 more minute than Tuesday. This time next week, there will be 1 less minute of sunlight. Next month we'll lose another 15 minutes. This continues until we've made another half trip around the sun at the Winter solstice on December 21 shortly after 6 a.m. That day we'll have only 9 hours 44 minutes of sunlight.
Why does the solstice happen?
The Earth's axis is tilted 23.5 degrees. During spring and summer months, that tilt is towards the sun producing longer days in the Northern Hemisphere. Wednesday, the Southern Hemisphere celebrates the Winter Solstice and its shortest days.
That tilt is the reason for Earth's seasons, not its distance from the sun. The planet is actually nearing the furthest point, or aphelion, in its elliptical orbit. This will occur on July 4.
You might expect today to consistently be the hotest of the year thanks to all that sunlight but it isn't. You might also expect the
Earth to be closest to the sun in its elliptical orbit at this, the start of summer, but surprisingly reality is exactly opposite. Earth
is actually nearing aphelion, or the farthest point, about 3 million miles farther from the sun than we'll be in December.
The solstice has been a time of celebration around the globe for much longer than we've understood any of the above.
Santa Barbara expects 100,000+ visitors for its 40+ year old celebration which features a lavish parade along with music and dance performances. In Sweden, the Summer Solstice is a national holiday marked with bonfires and parties. In England, special access is allowed to Stonehenge. Access is normally restricted to the site about 80 miles southwest of London but not today. Nearly 20,000 Druids, Pagans, astronomers, and tourists checking off on their bucket list are drawn to the site where they wait, some all night, to see the rising sun align with the Heel Stone, a pillar just outside the circle.
--Last week's question---
The correct answer to last week's question was "Alaska". Look for more questions in future blog entries.