Monday, March 27, 2017

The Evening Star Moves On!

For those of you who have been watching Venus in the evening sky, we've had a good show, but if you have looked in recent days it has disappeared! It is already sneaking into the morning sky and in another week or so should be visible to early risers coming up before the sun. But for those of us who have a telescope or for that matter, any optical aid at all, the last couple weeks Venus has been quite striking! If you have been a reader of this blog, you of course know that Venus orbits inside the Earth's orbit, so undergoes phases not unlike the Moon. It passed "Inferior Conjunction" a day or two ago on 25 March, where it passed between us and the Sun, so was "new" (using the same terminology we use for the Moon). In actuality, Venus passed the Sun from our vantage point about 8 degrees north of the Sun, so was never un-illuminated, but showed the skinniest of crescents. Behold the image at left - it was taken on 19 March. It shows about what it looked like thru a small telescope or good pair of binoculars. While a pretty view of a world the same size as the Earth, it is rather humdrum - kind of boring. Needs a little spicing up! On a field trip, I caught the crescent next to some cacti at Gates Pass, but with the darkened sky, the brilliant crescent is overexposed, and also likely a little out of focus with the cacti so near...

To the rescue comes my favorite foreground! Whenever there is something in the western sky, I generally head west of town and use the silhouette of Kitt Peak National Observatory as a nice foreground to frame the object(s). Whether for a comet and Moon, or some other close planetary conjunction, Kitt Peak has served many times to make a shot more interesting! I've actually attempted to catch Venus over Kitt Peak on the last inferior conjunction 18 months ago, but the geometry didn't work out and while I made a trip to look for it, clouds and a bright sky resulted in failure. This time, with Tom and Jennifer Polakis also taking part and calculating the setup position, we had a good chance. That is them at left, searching for the crescent even with the sun still up to verify that we were in the right spot to see it hanging over the Observatory. The silhouette of the Mountain/Observatory is always spectacular to me, and is shown at right in a 2-frame mosaic with the Canon 6D and TEC140 telescope (1,000mm focal length).

We didn't need to worry - Tom's calculations were spot on - he had worked towards it going behind the 4-meter telescope at right and sure enough, it did disappear behind the dome! That is my shot at left, with the still-slightly overexposed Venus crescent in the darkened sky.

It was interesting to note what a difference a meter or two makes in our observing position. At right is shown a single glimpse I got of the crescent appearing on the side of the 4-meter - you might have to click it to detect it to right of dome. Tom, a couple meters to the right of me, got a much bigger bite of it - his video clip of Venus setting is shown here. MAKE SURE YOU GO SEE IT!

As well as these exposures had come out, I was hoping for something a little better. A day or two later, Venus would be closer to the sun, the sky would be brighter and a shorter exposure would do better at keeping Venus properly exposed. As a result, on 21 March, I repeated the trip. Tom and Jenn couldn't join me, but advised me for positioning, advising a move to the south to get it behind the solar scopes. Unfortunately, there were no clear shots to the west where needed, so missed it going behind the south side of the Observatory. Still, the image of Venus was properly exposed. I also used a longer focal length - a 7" F/12 refractor made by Roger Ceragioli, resulting in a 2.1 meter focal length, more than double that used in the above image, and I also used the Canon XSi and its APS sensor, expecting considerable vignetting with the 6D. Interestingly, when I had first envisioned the shot 18 months ago, THIS was the shot that I saw in my mind! The colors on the Venus crescent is from atmospheric dispersion, since the Earth's air and curved surface combine to make it act like a thin prism. Seeing was also a factor as the features on the telescope, 12 miles away, and Venus, 26 million miles away, show structure and "waviness" from atmospheric turbulence...

Finally a minute or two later, Venus descended behind the water storage tanks atop the mountain. Using the profile of the mountain above, I was able to identify a couple other items seen in the photo, including 3 of the telescope domes...

I think it is amazing to capture planetary details with earthbound foreground, so would absolutely do this again. Will I try for the next inferior conjunction in October of 2018? More likely than not! What more fun can you have!?

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