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Dark Sky Park: Autumn Equinox

The Constellation Draco
The Constellation Draco

http://ipraudio.interlochen.org/2013-09-20%20Autumn%20Equinox%20-%20WEB.mp3

IPR: On our wall calendar it says that Sunday is the first day of Autumn. How is that so? What's happening to make that the date where we change from the Summer season to the season of Autumn?

MARY: Sunday, September 22nd is the day that the Sun appears to cross the celestial equator into the southern celestial hemisphere. This happens at exactly 4:44 p.m. our time and this is the moment when we have left the summer world of warmth and light behind and begun our sojourn through darker and colder times.

IPR: You said the Sun appears to cross the celestial equator. What do you mean by that? And what is the celestial equator?

MARY: All of these things are mechanisms created by human beings on Earth for orienting ourselves in space and these are not things that we can see or that are actually even happening - except that we do notice a change in the amount of light and in the temperature and so on.

We have to begin, then, with an imagination. So imagine yourself standing on the Earth which is suspended within a large sphere. We'll call this a "celestial sphere" and on it are all the stars. Now, we are slightly tilted and rotating within this sphere. So hold that image and then sense the center bulge of the Earth. We call this the "equator." You can project the Earth's equator out onto this celestial sphere and then you've created what is called the "celestial equator" which allows us to then speak about a northern or a southern celestial hemisphere.

Now remember, we are slightly tilted and rotating within this sphere while the larger sphere that we are within appears to remain stationary. This means the stars on the larger sphere are fixed in their places and, as we rotate, the stars appear to move, only it is we who are moving.

And here's where it begins to get tricky because, not only are we slightly tilted and rotating, we are also orbiting - so we're dealing with three different kinds of motion: tilting, rotating, and orbiting.

And into this mix we will place another celestial object - our Sun. And as we tilt and rotate we orbit the Sun at a particular rate and what appears to happen is that the Sun moves north and south of the celestial equator which is really our own equator projected onto this imaginary sphere. 

IPR: Is there another way that we can imagine this or are there stories that reveal what this point in the cycle of the year meant to earlier cultures?

MARY: An easier way to get hold of this is to imagine the cycle of the year as a breathing process. As human beings we breathe in and we breathe out: inhale and exhale. The Earth appears to do this as well but while as a human being I breathe on average 18 times a minute it takes the Earth one full year for a complete inhalation and exhalation. The exhalation comes at Summer Solstice when everything is as though "breathed out" into blossoms and the sprouting, fruiting world that reaches toward the Sun. And then the in-breath begins and the full inhalation occurs six months later at Winter Solstice when everything is pulled within; The fruits have ripened, the leaves have fallen, a blanket of snow covers the Earth which has now fully breathed into itself. 

From out-breath to in-breath we arrive at this midway point which is the Autumn Equinox and, for a moment, day and night are of equal length and then night grows longer and we have greater darkness to deal with. So here we find the cultural tales of the dragon slayer because the night and the dark are always related to these sinister creatures. And in the sky we see the tale of the Hydra, the water serpent, slip over the horizon and we see the constellation Draco overhead, wrapped around the pole star. And former cultures believed that the shooting stars we witness throughout these Fall months are like the shining sword of the dragon slayer, sending strength and courage to us through the dark.