Here is a picture of the sky some minutes after sunset on 19th March 2011, looking west across the city of Norwich. Actually it is a combination of 16 pictures through the 135mm lens on the Canon 350D. I didn’t combine in the usual way by pinning the stars down, but by just placing one on top of the other and each time just choosing the lighter of the two pixels from above or below. The result, I hoped, would tend to minimise the cloud by preferentially letting the lighter sky through. Luckily the camera was very still on its tripod through this period in which I was graced with a passing interested chap who had popped home to bring his wife along, at which point a plane decided to make my picture sequence a little more interesting. I wonder whether the crew and passengers knew that they were passing so close to the planet Mercury, the upper “star” and whether it looked like a huge bright ball out of their windows. I jest of course.The 16 pictures show the even descent of Mercury and Jupiter (the lower “star”) at the angle of <37.5º caused by the earth’s rotation. Mercury is at its widest separation left or west of the sun and the plane of its orbit pokes up northward from our perspective at spring dusk making it higher for us in the northern hemisphere. Mercury at this point is the same distance as the sun. On the other hand, we are waving bye bye to Jupiter as it is way beyond the sun and so is ‘sinking rapidly into the twilight’. The twilight is getting earlier as we approach summer, and the orbit of the Earth is moving so that the sun appears to approach Jupiter, which looks as bright as Mercury, but is 6 times further away. Mercury is moving more rapidly around the sun (88 days long is its year), so it appears to move with the sun and will stick around for a few more days, until it decides to pop up in the dawn sky for those nearer the southern hemisphere. While all this is happening in a darkening sky, I can see the Orion Nebula, Sirius the Dog Star, and in the cold wind the so-called supermoon is rising behind me. The closest point of its orbit has happened to coincide with full moon as it’s swinging around us on Earth. From my perspective on this rotating spheroid, Jupiter had disappeared and been replaced with a very bright patchy grey face shining through the trees. Naked-eye astronomy is pretty inspiring sometimes.
