Another Trip
Round the Sun

5 February 2014

A candle in the dark. Jon Sullivan
A candle in the dark.

We often measure our lives in terms of the Sun. Relative to the stars, the Earth rotates once every 23 hours and 56 minutes. But we like to measure our days from noon to noon (or midnight to midnight), and that takes an extra few minutes because of the Earth’s motion around the Sun. So we measure a day as 24 hours. The motion of the Earth around the Sun also means the Sun appears to move across the sky relative to the stars. About every 365.25 days its path repeats itself.

Well, not quite. The Sun is moving relative to other stars. The solar system is orbiting the galaxy about once every 240 million years. So by the time the Earth makes a complete circuit around the Sun it hasn’t really returned to its point of origin. But because even the closest stars are light years away, their motion over a year is small, and so the Sun appears to return to its same position in the sky year after year.

And because the Sun governs the seasons, and we mark our days on the cycles of the Sun, we give a certain significance to the days when the Sun returns to the place that marked our birth. Perhaps it is a last remnant of that ancient and debunked astrology. Perhaps it is our nature as astronomers. Whatever the reason, we mark these days, and ponder their significance.

And on these days, for some strange reason, we like to put small wax pillars onto sweet baked goods and set them on fire.

Such is life on this small planet.