Moon and Saturn

The chart said these would be due south at 3.30am on 21 March, elevated 18° above the horizon.  A quick check the previous evening showed that the gap between the tree and the neighbour’s house, viewed across the top of my shed, would just give me an unobstructed view.

I was still awake at 1am, kept getting up to see whether the clouds had cleared, and was surprised when the alarm woke me at 3.00.  I opened the west-facing bedroom window to stick my head out, and saw clear sky to the south – with the Moon exactly as predicted.

Set up the tripod, mount the new Altair Wave 115 – with the Nikon attached as if to an 805mm f/7 lens.  After years of SLR photography, I still think in terms of focal length rather than objective lens diameter.  The field of view with this combination is 1.68° x 1.12°, perfect for this shot as Saturn was just 1.2° from the Moon.

Focusing was very easy with the Bahtinov mask and the dual speed focuser, especially with the Nikon’s LiveView screen zoomed right in on Saturn.  Even though Saturn is a ringed disk rather than a point of light, the changing shape of the view through the mask was obvious.

At ISO 400, trial and error gave 1/250th of a second exposure for the Moon, and 1/30th for Saturn.  By 4am I was quickly layering these together in Photoshop…

The Moon and Saturn separated by one degree
805mm f/7 ISO 400 1/250 sec (Moon) 1/30 sec (Saturn)

…and back in bed at 4.15, just as the clouds returned.

Stitching!

I now write a regular piece for the Eddington Astronomical Society, setting out what’s going to be on view in the night sky each month. In all honesty, it will probably lean towards astrophotography!  You can see the March 2014 version here.

One of the opportunities identified as coming up in March was the view of Jupiter reaching its highest point in the sky, elevated 59° in the early evening of the 13th. This looked like a challenging photo project, with bright Moon, bright Jupiter, bright and faint stars and the inevitable Morecambe Bay glow. It would also be at its best during twilight.

Sadly the Cumbrian rain was forecast for that evening, but we enjoyed a few days of high pressure just before then, with a couple of clear nights.

On Tuesday, 11th March, I strolled up to the Mushroom on Scout Scar with no more than camera and tripod. The 18-200mm zoom is pretty wide at 18mm, but I wanted a field of view of about 150°, so I set it to 24° and took nearly forty frames in a grid pattern looking south.

Photoshop can stitch shots together to make panoramas, but it needs clear points of reference in the shots and can only run on automatic. So, if it can’t identify the overlapping shots itself, there is no option for user-intervention. It simply doesn’t work on night sky mosaics.

That’s when I found PTGui, a programme that does exactly the same, but with a much wider range of projection options and, most importantly, the facility for the user to identify the overlap points (ie the stars) manually.

Here is the result, the view south from Scout Scar, Tuesday evening13th March. The sky isn’t flat, of course, and stitching frames requires distortion according to various rules depending on the projection settings. Circular projection seems to give the best compromise on distortion, then I cropped the result to a nice tidy rectangle.

All frames ISO 1600, 10 seconds 24mm f/5.6.

Big sky! Nearly 40 frames each 10 sec ISO 1600, 24mm f/5.6, stitched in PTGui