In the solar year, there are four significant dates:
- Northern winter solstice (December 21 or 22), when the noon Sun is directly overhead at the Tropic of Capricorn in the southern hemisphere. This means the Sun is at its lowest point in the sky from the perspective of the northern hemisphere, making for the least amount of daylight and the longest night. In the southern hemisphere, of course, this is the longest day and the shortest night, so the northern winter solstice is the southern summer solstice. This day is also known as Midwinter’s Day or Yule. The date of Christmas was originally selected for its proximity to Yule, though changes in the calendar have moved it a bit.
- Vernal (or spring) equinox (March 20 or 21) is when the noon Sun is directly overhead at the Equator. In the northern hemisphere, are lengthening at that time, while days are shortening in the southern hemisphere. The festivals of Passover and Easter are calculated from the date of the vernal equinox (with extra complications having to do with the phase of the Moon).
- Northern summer solstice (June 20 or 21), when the noon Sun is directly overhead at the Tropic of Cancer in the northern hemisphere. Also known as Midsummer’s Day, this is the longest day and shortest night in the northern hemisphere, but the shortest day and longest night in the southern hemisphere.
- Autumnal equinox (September 22 or 23), like the vernal equinox, finds the noon Sun directly overhead at the Equator.
In addition, there are four lesser-known festivals halfway between the major festivals:
- Groundhog Day (also known as Candlemas) is halfway between the winter solstice and the spring equinox. This is the significance of the “6 more weeks of winter” in the Punxsutawney Phil myth in the United States (itself derived from various European traditions): it’s approximately 6 weeks from February 2 until the vernal equinox.
- May Day (also known as Labor Day) is halfway between the spring equinox and summer solstice.
- Lammas (which I imagine many people haven’t heard of!) is halfway between the summer solstice and the autumnal equinox.
- Halloween (moved like Christmas from its original date, celebrated in Mexico as Day of the Dead) is halfway between the autumnal equinox and the winter solstice.
So Groundhog Day has drifted pretty far from its roots, but that’s OK by me. We don’t have to assign deep meanings to dates that simply are due to the natural motion of the Earth around the Sun, and I think all of us can enjoy a festival whose primary modern purpose is to look at small fuzzy animals.
(This post is a slightly edited rerun from last year.)