# 6.2: Equinox and Solstice

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In particular, the angle between the Earth's axis and the Earth-Sun line changes throughout the year. Twice a year, at the spring and fall equinox (around March 21 and September 22--the exact date may vary a bit) the two directions are perpendicular.

Twice a year, the angle is as big as it can get, at the summer and winter solstices, when it reaches 23.5 degrees. In the summer solstice (around June 21) the north pole is inclined towards the Sun, in the winter solstice (around December 21) it faces away from it.

Let us look at the summer first, with the Sun on the left.

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