Every now and then I'll be in the right place at the right time to see the moon rising just above the horizon. Sometimes it appears to be absolutely, incredibly, amazingly, ginormously huge. Similarly, sometimes when the sun is setting, it appears to be much bigger than usual (as a kid I used to worry that it was poised to explode).
Of course, neither the moon nor the sun actually changes size. In the case of the moon, for example, if you hold your hand out at arm's length, you can compare it to the size of your fingernail when it's low on the horizon and later when it's high in the sky. If you perform this simple experiment, you'll observe that the moon is the same relative size in both cases (don't try this with the sun because its too bright and you don't want to damage your eyes).
Well, I just saw a Fantastic Picture at PhysOrg.com showing a time-lapse sequence of the moon rising over Seattle. In this image, you can see that – as far as the camera is concerned – the moon appears to be the same size no matter what its location on the sky.
The interesting thing is that no one knows why the moon appears bigger to the human eye when it's close to the horizon. There are lots of theories – such as the fact that we subconsciously compare it to objects like trees whose size we know – but no one knows for sure.
Questions? Comments? Feel free to email me – Clive "Max" Maxfield – at firstname.lastname@example.org). And, of course, if you haven't already done so, don't forget to Sign Up for our weekly Programmable Logic DesignLine Newsletter.