Stargazing

By Ken Campbell

Summer Solstice

The Earth is not standing straight up on its end, it is tilted by about 23 ½ degrees, and it is this tilt that causes the seasons. In the Summer the Northern hemisphere is pointed towards the Sun and in the Winter the Earth has gone half way round its orbit of the Sun and now the Southern hemisphere is pointed at the Sun.

This tilt causes winter days to be short and summer days to be long and this weekend is the longest day of them all. It is called the Summer Solstice. At exactly 2 am on Saturday morning 21st June the Earth will be tilted as much as it ever can be towards the Sun.

The Earths tilt is so pronounced that on the Solstice in countries above about 60° latitude the Sun doesn’t set at all and remains in the Sky throughout the night, giving rise to the term ‘land of the midnight Sun’. For a reference, John o’Groats, the most northerly point in mainland Britain is at a latitude of 58 ½ °. So from here there would be twilight all night long.

Map makers have conveniently placed imaginary lines around the Earth to indicate the extremes of the Earths tilt. Running around the middle of the Earth we have the Equator line. Here the Sun is directly overhead on March 21st and September 21st these dates are known as the Equinox. 23 ½ ° north of the equator is a line known as the Tropic of Cancer. It is on this line that the Sun will be directly overhead on the Solstice. And at 23 ½ ° south of the Equator is another line called the Tropic of Capricorn where the converse is true and the Sun will be directly overhead on December 21st.

The Arctic Circle is the point where the Sun never sets on the Summer Solstice and doesn’t rise on the Winter Solstice.

Here in Southern Spain we are at about 36 ° north and two hours ahead of Greenwich mean time, so if you stand outside at 2 pm on Friday or Saturday afternoon the Sun will be as high in the sky as it can get and you will have virtually no shadow as it will be almost directly beneath your feet.    

In pre-history times, the Pagan religions celebrated this day with so much vigour that it is believed that Stonehenge in southern Britain was constructed to commemorate this day. From Stonehenge the Sun will rise directly over a particular stone called the Heel Stone and its rays will travel straight into the center of the stone circle. Thousands of modern day Druids will be flocking to Stonehenge this weekend to celebrate this ancient festival.

So if you have a sudden urge to dance naked through the forest and sacrifice the odd goat, then you can always blame it on the Summer Solstice.

For more updated news on Astronomy and details of the mobile Planetarium Check out my website www.kencampbell.info   

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