(c) Anthony K. Grafton 2003

And the Sun Stood Still

In a recent Science Corner titled “The Length of Days” the tilt of the Earth on its axis was used to explain why our winter days are short and the summer days are long. In just a few weeks, we’ll be reaching an important seasonal milestone: the spring equinox.

The word equinox means that at this time of year, the length of daylight and dark are equal. At the equinox, the Earth is oriented so that the sun rises and sets directly over the equator. This happens again in September when we reach the autumnal equinox. As we move past the spring equinox, the daylight will last longer and longer as the tilt of the Earth points us more and more towards the sun.

Around the 21^st of June we’ll reach the summer solstice. This is the beginning of summer, and the time when the amount of daylight reaches a maximum. The word solstice means that the sun appears to stand still. In other words, the sun appears to rise in the same location for several days in a row, whereas at other times of the year, the sun rises at a different place every day. We also can recognize the winter solstice in December, when the amount of daylight reaches a minimum.

Ancient cultures viewed solstices as important events since a celestial body appeared to be changing its behavior. You can track the rising of the sun yourself with a piece of paper taped to an east-facing window. Draw a line on it tracing the horizon. Stand in the same place every morning and mark and date the place where the sun rises. At what time of the year does this location change the fastest?