The Not-So-Equal Equinox
Observing > There are four important points in earth's orbit around the sun, three of which get a lot of glory, the last of which "falls" by the wayside. They are the solstices and equinoxes.
Three of these guys get the big press. The spring equinox is a traditional "first day of spring." Several high holidays, like Passover and Easter, are embraced around this time. The summer solstice gets credit as the first day of summer and is fêted as the "longest day." And winter solstice finds itself fully immersed in tradition and ritual for as far back as we have records. Peoples throughout the northern hemisphere have made that time into a time of great celebration and/or revelry.
Then we have the forlorn, almost unnoticed fall - or autumnal - equinox. We celebrate this event on Monday, but with about as much fanfare as the coming of the new phonebook. So, in our continued attempt to occasionally focus here on the so-called "less important" things, let's take a closer look at this fall equinox.
First, though, we have to understand what on earth a solstice or equinox is. This is going to take into account two of Earth's motions: its orbit around the sun and its tilt. Ready?
You know that our planet revolves around the sun in about 365 days. Moreover, we rotate on an axis once every 24 hours. But the axis of our spin is not perpendicular to the plane of our orbit around the sun - we are tilted over with respect to it. Our spin axis doesn't give a tinker's cuss for the sun; it is lined up with the North Star, Polaris, for as long as we all shall live.
This tilt allows us in the northern hemisphere to sometimes be tilted towards the sun, sometimes away. When we are tilted towards we have the long, hotter days of summer. When tilted away we have shorter days and the weather cools. We are tilted most toward the sun on the summer solstice, most away at the winter solstice.
But it follows that sometime between the days that we are tipped towards the sun and those we are tipped away, there must be a time we are not angled over at all with respect to the sun. These are the equinoxes. We have one of those at the end of March, and one now.
On the equinox the sun will shine on earth from pole to pole. The sun will rise due east, be up for 12 hours, set due west, then be down for twelve. The "daytime," however, will not be really equal to nighttime as the name equinox implies. There are several hi-tech reasons for this inequality which take into account the specifics of true horizon, the size of the sun, and atmospheric refraction, and so on.
But the most obvious reason that daytime wins over nighttime on the equinox is because of twilight, that time before the sun rises and after it sets when the sun still lightens the skies. In Southern California the twilight brackets the "day" for about an extra hour before and after the sun is up.
But at the poles thing are not so ordinary on this day. You might remember from school that on the equinox a person standing at the equator at solar noon will see the sun directly overhead. But put yourself at a pole and you'll see the sun actually going around the horizon like a great blinding ball of light all day long. At the North Pole these are the last days to see the sun for a while as the earth now tilts away from our star causing it to slowly sink below horizon. All this puts the pole in a creepy twilight until we are tilted so far over that from November until January it is nighttime all day long there.
There are precious few holidays on the planet that celebrate this day. Maybe you can start one, one which is filled with thanks for the beautiful fact that our planet is not always lined up perpendicular to the sun. Initiate a holiday that celebrates our whole array of seasons and changing weather and varied climates and maximal living area on this planet, all effects which find their cause in the perfect tilt of our planet.
Posted by Mark Ritter at 2008.09.21 09:45 PM | Comments (0)
