Right Angle Moon


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.

– Alan, September 23, 2012 / © 2012 Alan Dyer

 

Moon over Saskatchewan River Crossing


 

This is how the night started, on Sunday evening, September 4 — as clear a night as you could ask for in the mountains. A quarter Moon hangs over the peaks of the Continental Divide, with alpen glow, the last rays of the Sun, illuminating the mountains around Saskatchewan River Crossing, in Banff.

The North Saskatchewan River flows east out of the mountains here, after being joined by the Mistaya and Howse rivers. It was here, in the early 1800s, that David Thompson and his party of fur traders from the North West Company entered the Rockies and heading up over Howse Pass off frame to the right, to trade with the Kootenays in the interior of what is now British Columbia.

This is David Thompson country, named for one of the world’s greatest geographers and mapmakers. He mapped most of western Canada and down into the Oregon Territory. All using compasses, sextants, a Dolland refractor telescope (to observe the moons of Jupiter for telling time), and his skills as an astronomer. The Kootenays called him Koo-Koo-Sint — the man who watches the stars.

It was also here, on these open river plains, that James Hector, mapping southern Alberta with the Palliser Expedition, observed Comet Donati in September 1858.

This is a place in the Rockies with many ties to history and to astronomy.

— Alan, September 5, 2011 / Image © 2011 Alan Dyer

Moon in the Mountains


I’ve been chasing the Moon this week. I caught up with it last Thursday night, August 4, in Banff, with the waxing crescent Moon low in the southwest at dusk.

The location is the upper Vermilion Lake just outside the Banff townsite. The golden reflection of the low Moon on the water, the slope of the mountainside and its reflection, the dock and steps, and the tail lights from a vehicle on Highway 1 just up the hill (I decided to leave them in!) make for what I think is an interesting composition of converging lines.

I got set up and in position just in time to catch the scene at the magic hour of twilight, when the sky is dark enough the show deep colours and the Moon’s entire disk shows up, but before the sky gets too dark and the Moon too bright to make an interesting scene.

Even so, the contrast in such a scene is still very high. So to capture it more as your eye would have seen it I used a stack of five exposures, taken in rapid succession, each 2/3rds of an f-stop apart. I then merged the frames with Photoshop’s High Dynamic Range routine to create a scene that brings out detail in the foreground without overexposing the Moon and sky.

A technical method to capture a simple scene of serenity in the mountains.

— Alan, August 7, 2011 / Image © 2011 Alan Dyer