The Moon Illusion

After sleeping for most of the day, I suspect because of the antibiotics and also my body wanting to shut down after this week (woke at 10.30am, went back to sleep at 1.30pm, woke just before 8pm) I felt that I needed to get out of the house.

I had a purpose. The moonrise was beautifully timed to occur as sunset was ending and with it being almost full (97%, Waning gibbous), I knew that it would provide a spectacular view of the "Moon Illusion". Neither Corin nor James have ever seen moonrise so it proved to be a nice little educational outing!!!

5 minutes walk from home, at the back of the railway station, we have a 180 degree clear horizon view from North to South. Perfect setting.

There is much written about the moon illusion and it appears to have raised questions about why the moon appears to be so much bigger when close to the horizon than when it is viewed high in the sky. Aristotle apparently attempted to answer the question and astronomers ever since have provided theories about it. It appears that the best answer is related to how our eyes view objects - with the angle of view being low and our eyes having reference points on the horizon, our mind is tricked into believing that the moon is much bigger.

The redness that colours the moon when it is low like this (and this varies during the year) is related to the timing of the moonrise and the scattered light that remains. By the time moonrise occurred, blue/green light had already been scattered, leaving the red/yellow light of the sunset to colour the moon through reflection.

Note: The image is straight out of camera aside from a crop. Taken on tripod, zoomed to 216mm as the horizon, housing etc are at the far side of a very large area of farmland.

Science is very cool.