Summer solstice in 2011 was celebrated by many countries in the Northern Hemisphere. There, it marks the longest day of the year, the shortest night of the year, and what many consider to be the beginning of summer.

Many people took the occasion to observe the skies and welcome summer. Meanwhile, it was winter solstice for the Southern Hemisphere and the opposite conditions for them.

Come December, it will be winter solstice in the Northern Hemisphere and summer solstice in the Southern Hemisphere.

The two solstices of the year occur when the earth's tilt towards the sun reaches an extreme point. In the June solstice, the Northern Hemisphere is tilted towards the earth while the Southern Hemisphere is tilted away from the earth.

A man uses a camera on a rocky crest filled with astronomical markers during the summer solstice at the Kokino megalithic observatory June 21, 2010. The 3,800-year-old observatory was discovered in 2001 in the northwestern town of Kumanovo, 70 km 43 mile
A man uses a camera on a rocky crest filled with astronomical markers during the summer solstice at the Kokino megalithic observatory June 21, 2010. The 3,800-year-old observatory was discovered in 2001 in the northwestern town of Kumanovo, 70 km (43 miles) north from Skopje, and is ranked as the fourth oldest observatory in the world, according to NASA. Reuters
A man uses a camera on a rocky crest filled with astronomical markers during the summer solstice at the Kokino megalithic observatory June 21, 2010. The 3,800-year-old observatory was discovered in 2001 in the northwestern town of Kumanovo, 70 km 43 mile
A man uses a camera on a rocky crest filled with astronomical markers during the summer solstice at the Kokino megalithic observatory. The 3,800-year-old observatory was discovered in 2001 in the northwestern town of Kumanovo, 70 km (43 miles) north from Skopje, and is ranked as the fourth oldest observatory in the world, according to NASA. Reuters
A man celebrates the summer solstice at the Kokino megalithic observatory June 21, 2008. The 3,800-year-old observatory was discovered in 2001 in the northwestern town of Kumanovo, 70 km 43 miles north from Skopje, and is ranked as the fourth oldest obs
A man celebrates the summer solstice at the Kokino megalithic observatory June 21, 2008. The 3,800-year-old observatory was discovered in 2001 in the northwestern town of Kumanovo, 70 km (43 miles) north from Skopje, and is ranked as the fourth oldest observatory in the world, according to NASA. Reuters
Winter