Summer Solstice

Happy Summer Solstice!

Summer officially arrives at 18:06 GMT (that means 6:06 PM in Merrie Olde England) . Since I’m on the West coast of the USA, it will be arriving a bit earlier in the day for me. Pacific Daylight Time is GMT – 7 hours. So 18:06 – 7:00 = 11:06.

I know that some of the readers of this blog are fairly young, so I’ll explain what is going on. Those of you who already know what the solstice is can skip over the rest of this post.

The solstice is defined in terms of the motion of the Earth around the Sun. The term ‘Summer Solstice’ is commonly used for the solstice that occurs in June. However, the more proper name is ‘Northern Solstice’. The Northern solstice corresponds to the longest day in the Northern hemisphere, and the shortest day in the Southern hemisphere. It marks the beginning of summer for us, and the beginning of winter for someone living south of the equator. It corresponds to the point at which the sun is directly over the Tropic of Cancer on your globe.

As the Earth orbits the Sun, it describes an ellipse (not a circle, but a sort of egg-shaped or oval-shaped curve). If you were to think of a flat surface laying on that ellipse, it would pass through the Sun. The Earth’s axis (the imaginary line around with the Earth turns every day) is tilted in relationship to that plane. As the Earth moves around the sun the axis keeps pointing in the same direction, just like a toy gyroscope keeps pointing in the same direction if it is sitting on your hand and you move it in a circle. So because the axis is tilted and always points in the same direction, some parts of the year it is leaning toward the sun, and other parts of the year it is leaning away from the Sun. The Northern solstice occurs when the line of the Earth’s axis passes directly over the northern pole of the Sun.

This is what gives us our seasons. As the Northern hemisphere is tilted toward the Sun, we have summer, and the Southern hemisphere has winter. As the Southern hemisphere is tilted toward the sun, the seasons are reversed.

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