The Myths of the Equinox

This Saturday at 6:54 pm PDT the Sun will be directly over the Equator. Geographically, the event will occur over the western Pacific Ocean, north of Papua New Guinea (≅149° east longitude.) It is the Autumnal Equinox and it is the moment that summer ends and winter begins…in the northern hemisphere. In the southern hemisphere, the equinox is the end of winter and beginning of spring.

Equinoxes are ripe with myths, but probably the most common myth is that an equinox is a date of an equal day (12 hours) and night (12 hours.) It is a myth established by those who live in the mid-latitudes because, on the day of the equinox, the day and night are approximately equal. Near the equator, the length of day and night are nearly the same year-round, so the equinox has no significance.

Equal Day/Night is About Location, Location, Location

Near the equator, day and night are almost equal the entire year; however, the closer one is to either pole, the length of the day increases to the point that there is no night on the equinox. Most locations away from the poles do have a date when day and night are approximately equal, but that rarely occurs on the equinox.

In Panama City, Panama, October 6, 2018, is the date when day and night are equal. In Reno, Nevada, USA, the date is September 25th. In New York City, NY, USA the date is September 26th. In São Paulo, Brasil it is September 17th. The date occurs near the equinox, but the exact date varies depending on location.

Finding East and West on the Equinox

What is true about the equinox? The equinox is the date that an observer can determine true east and true west from her or his location if she or he has an unobstructed view of the sunrise and sunset. Why this happens is complicated, but the point on the horizon where the Sun rises is true east and where it sets is true west.

Don’t get me started about balancing an egg. Eggs are for eating regardless of the date…and that’s about it.