September 23, 2012 – The Amazing Sky

At equinox the Sun sets due west and shines into the eyes of drivers heading west into the sunset.

This was the scene Friday night on Highway 1, heading to Banff out of Calgary. I set up beside the highway to catch the scene of the Sun going down at the end of the road. I was hoping for more smoke and haze to dim the Sun to a clearly defined disk rather than deal with a bright glow. But you shoot what the sky gives you.

This is one frame from a 315-frame time-lapse movie of the traffic madly moving down Highway 1 (a true to life recording!) and the Sun glow setting behind the Rockies.

Saturday night was a fine evening for witnessing the geometry of the night sky.

This is sunset on the evening of the autumnal equinox, September 22, 2012, with a first quarter Moon in the sky. The image illustrates the geometry of the quarter Moon’s position, which is always 90° away from the Sun, a quarter of the way around its orbit in its monthly cycle.

In this case, because the Sun (at right) was on the equinox position on the ecliptic, it was setting due west this night (something it does only on the dates of the fall or spring equinox). This put the quarter Moon (at left) 90° away, due south at sunset.

Draw a line from the Moon to your eye (the camera) and then back out to the Sun and it forms a 90° right angle. This geometry holds true for any quarter Moon, but being equinox the Sun and Moon were nicely aligned due west and south, making their right angle arrangement more obvious.

I took this shot from the grounds of the Rothney Astrophysical Observatory on the occasion of their monthly Open House.