Tuesday, 18 October 2016

1 lux in the moonlight

Here's the full moon reflecting off a white wall. The camera is not as good a light collector as my eye. I could even see my shadow on the ground, which would not come out in a photograph. A full Moon on a clear night gives up to 1 lux. Further to yesterday's post about the perigee Moon looking bigger, I suppose the simplest thing to do with the apparent size is to square the angle subtended at the eye to give some sort of angular area subtended. At perigee that would be 9.59 milliradians to be squared giving 92.0. At apogee it would be 8.57 milliradians squared giving 73.4. The perigee Moon should look 92.0/73.4 = 1.25 x bigger or 25% bigger. I'm getting closer to the 30% figure commonly given.