I hate crossword puzzles, I really hate them passionately. I think my awfull speling could be partley to blame. This does not mean I do not like puzzles.

This morning I spotted an astronomy/navigation puzzle that got me thinking. The puzzle is from Tristan Gooley, who wrote an excellent book that has loaded me up with intresting observations to take with me when out with groups on the hills. I had an idea when I first read it but had to save it to later when I could spend more time on it. So now, here it is; a lovely nerdy puzzle.

The picture is a star trail picture that can be used to find out

1 – Which hemisphere was the picture taken in?

2 – At what latitude was the location?

3 – How long was the exposure (I threw this question in myself as I was curious)?

4 – In which direction was the picture taken?

The first challenge was relatively straight forward as each line on the picture represents a star and looking at them for a while I recognised none of the constellations that we see spinning around the pole star, which points to North here in the Northern Hemisphere.

I don’t recognise any of these star patterns.

So, I assumed the image was taken in the Southern Hemisphere, with the stars spinning around the south pole.

The latitude, I confess, I did not try and figure out as it said it in further down in the puzzles webpage and unfortunately I read it and spoilt that part of the conundrum.

The exposure length was a wee bit trickier and required measuring the length from the south pole (below the horizon) and the length of the star trail. Along with some GCSE maths this gave me the angle the stars had moved through during the length of time over which the picture was taken. The answer was four degrees.

If we assume that it takes 24 hours for the stars to turn around 360° (actually it is us that is turning) then that works out to be four minute per degree, or sixteen minutes for four degrees. I would not be surprised if I was a degree or so out and I think the camera exposure could be between twelve and twenty minutes.

The exact direction that the camera was pointing took a little longer to figure out (and Stellarium).

Marking the stars….

….then removing the image…

top half from the picture/bottom half Stellarium

…left me with an image I could use with Stellarium to try and match up some patterns.

top half from the picture/bottom half Stellarium

These are not constellations I recognise, but making up some random lines between them helps to see that they are a match.

top half from the picture/bottom half Stellarium

This means the picture was taken pointing at 160°.

Nice! Far nicer that a crossword puzzle.

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