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Dalriada n:
Kingdom of the Scots,
home of the residents

Lunar occultation of Aldeberan

Sky at Night (SaN) magazine had a piece on this:

WHEN: 5 September, 05:30 to 07:10 BST (04:30 to 06:10 UT)
The Moon has been making close passes of the bright star Aldebaran (Alpha((1) Tauri) for a few months now, but on the morning of 5 September, the two will finally meet — kind of. While in reality Aldebaran will be around 1.4 billion times farther away, from our perspective the Moon’s edge will at least appear to pass in front of the star.

Like all stars, Aldebaran is so distant that it looks like a point source of light. The Moon has no atmosphere, so when its edge covers the star, Aldebaran will disappear instantly.

…followed by 2 whole pages on how to photograph it, which involved a complicated multi step-by-step guide and more astrophotography kit than I’ve got. So I determined to have a go anyway, with my Canon DSLR camera and my SkyWatcher Explorer 200P (Newtonian) telescope. I expected the hard part would be to include Aldeberan and the Moon while not underexposing the former or overexposing the latter.

So I set up my kit in the garden and set my bedside alarm clock for 05:00 -luckily the weather looked promising! At 05:30 I was surprised and delighted that I could discern the star and the moon in the camera’s preview window – and capture a reasonable image of both with quite a short exposure, 1/20s at ISO 100. Then I set the remote release gadget to take 1 shot every 20s and let it get on with it.

The animated gif below includes 50 images and loops continually. It’s a bit jerky as I made some adjustments but you can just about make out the star as it appears to approach the moon from the left. The mount was supposed to be tracking at the lunar rate, not the sidereal rate (which should render stars ‘stationary’) so the moon should be fairly static in the frame, while the star ‘approaches’ it.


And here’s a monochrome, stacked image of the same thing, using Gimp (GNU Image Manipulation Program) to align and stack and sharpen the same 50 images instead of creating an animated gif.stackedmoonsharpened

Finally, here’s a Cartes du Ciel screenshot of the same thing, as if from the same place at the same date/time with the same camera and telescope.cdcshot

The star was due to reappear from behind the moon’s dark edge on the right at about 07:10, but sunrise was at 06:29 so it would be quite hard to spot! I went to bed and left the camera to it – with lots of photoshop processing I can just discern the emergence but you would not be impressed.

Next stop is SaN’s don’t miss – top sight of the month (weather permitting) a triple lunar event in the morning of 28th September. It’s a Harvest Moon because its the closest full moon to the autumnal equinox, and it’s the largest full moon of the year, and it is totally eclipsed by the Earth’s shadow, a lunar eclipse.