Summer solstice 2011 is upon us in the Northern Hemisphere.

Scientifically speaking, the two solstices in a year are the days during which the earth's tilt towards the sun is the most extreme. For the solstice in June today, the tilt is towards in the sun in the Northern Hemisphere (summer solstice) and away from the sun in the Southern Hemisphere (winter solstice).

For the solstice in December, it's the opposite.

The science aside, most people think of summer solstice as the beginning of summer and the day of the year with the longest period of daylight.

Below are pictures of individuals celebrating and observing the summer (and winter) solstice around the world.