21st June 2010 – Summer Solstice

Today is the Summer Solstice.

What does this mean for regular folks? Well not much… Mostly it means that today is the longest day and at midday the Sun is as high in the sky as it gets during the year. In many countries this day marks the start of summer. Happy days…

Astronomically it is the day when the Earth’s axis tilt is most inclined towards the Sun. In the northern hemisphere this happens around the 20th or 21st of June and in the southern hemisphere around the 21st or 22nd of December.

The Sun photographed at the same time of day throughout the year

In the image above (taken from APOD) the Sun is photographed at the same time of day throughout the year. The path it traces is called an analemma. Summer Solstice occurs on the day the Sun is at its highest. The figure of eight is caused because the Earth’s orbit is slightly elliptical and the Earth moves faster in its orbit when closer to the Sun. This means that in some parts of the year the Sun is further along in its path over the sky and at others it is behind.

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