Longest Day...

Today is the longest day of the year in the Northern Hemisphere. 

The June solstice is here once again, marking the longest daylight period of the year and the start of astronomical summer in Earth’s northern hemisphere.

At 5:04 UTC (1:04 a.m. EDT) on June 21, the sun can be seen straight overhead along the Tropic of Cancer, while the North Pole reaches its maximum annual tilt toward the sun. As the planet rotates on its axis, areas within the Arctic Circle see the sun circle through the sky for 24 hours.

Of course, in the mid-latitudes of the Northern Hemisphere we don’t see the sun up for 24 hours, but there’s still plenty of daylight to enjoy. Most places in the continental U.S. see the sun above the horizon for 14 to 16 hours on the summer solstice – the exact amount depends on your latitude.

On the summer solstice, areas of the Northern Hemisphere outside the tropics see the longest daylight period of the year and the midday sun is at its highest point in the sky.
In Washington, D.C., the sun is above the horizon for 14 hours and 54 minutes, climbing 74.5º above the horizon at solar noon (1:10 p.m.). The higher your latitude, the longer you’ll see the sun above the horizon – however, this also means the sun will appear lower in the sky.

In the table of world cities below, we see that in more northern locations, the sun is up longer on the summer solstice, but shines from a lower angle at midday. Compare Washington and London, for example: The sun in London (if not masked behind clouds), is up nearly two hours longer than in Washington. However, at midday it’s only as high in the sky as Washingtonians see it in mid-April.

Why can’t we say that the sun is at its highest point in the sky everywhere north of the equator? The reason is that in the tropics (locations within 23.5º latitude of the equator), the midday sun can appear toward either the northern or southern horizon depending on the time of year . Along the equator, the noontime sun is at its highest point – zenith – on the equinoxes, while on the solstices, the sun actually takes its lowest path in the sky.

Interestingly, the June solstice sun appears higher in the sky at solar noon in cities like Washington, New York, or Minneapolis than it does on the equator. As we see in the first table above, equatorial Singapore only sees the sun rise 67.9º above the horizon on the summer solstice, while the sun in Minneapolis appears at a slightly higher 68.5º above the horizon at midday


Read More : 

http://goo.gl/OacHc