wall@fortune.UUCP (Jim Wall) (02/16/84)
Well, I've thought about it. Checked several times on several different occasions. But I'm sorry, there is just no way that the moon appears larger on the horizon just because of an optical illusion. Sure, it was a good try; I mean putting the guilt on us to believe that we were taken in my a mere illusion. So as a result of embarressment, no one spoke up, and you all won the round. But the time of truth has come. I mean to say that we had a very (reads: VERY) large full moon just over the horizon today, sort of peaking out from behind a few clouds. Now I first imagined that same size in the middle of the sky (also with some clouds around) and it would have still been huge. Now, no one is saying that there was an actuall change in physical dimensions or mass of the afore mentioned lunar object. But it sure looked larger than normal, and it was not (picture the stamping of foot and tensing of face to indicate firm belief), I repeat not, just because it was near some common reference points. Oh, I lsot one of my trains of thought (I know: they must be pretty narrow gauge), I even compared the size of the moon with a dime held at arms length, and then held that very same dime up and got a relative size to some clouds that were overhead. Yes, we are talking large moon. Much larger than you see on cold winter nights when it is straight over head. Lets revise the old atmospheric magnification ideas, or perhaps the visitors from another planet, no, wichchraft, yes that's it I'm sure! -Jim
labelle@hplabsc.UUCP (WB6YZZ) (02/17/84)
agree totally, I ran a similar experiment. There must be some atmospheric affect at work.
kissell@flairvax.UUCP (Kevin D. Kissell) (02/17/84)
(Sigh)
When the moon is on the horizon, its image passes through more of the
atmosphere than when it is overhead. This *can* affect the size (and
shape) of the image slightly. The usual effect (or so an astronomer
once told me) is that the image of the moon is *smaller* on the
horizon than overhead. Next time you want to try an experiment,
instead of looking at the moon on the horizon and "imagining what it
would look like overhead", take photographs with a fixed focal-length
lens of the moon both on the horizon and overhead, preferrably on the
same night. Then measure the resulting images.
Kevin D. Kissell
uucp: {ihnp4 decvax}!decwrl!\
>flairvax!kissell
{ucbvax sdcrdcf}!hplabs!/leeway@sdcrdcf.UUCP (Lee Gold) (03/24/84)
THE MOON ILLUSION quoted from ELEMENTS OF PSYCHOLOGY by Krech & Crutchfield The smaller apparent size of the moon when seen high in the sky is related to the upward tilt of the eyes in the head when looking upward. To check this, lie on a tilted board so you look directly at the moon riding high in the sky without having to raise your eyes in your sockets. The moon will look as large as it does on the horizon. The primary source of this (disillusioning?) information is E. G. Boring, "The Moon Illusion," American Journal of Physics II, 1943, pp. 55-60. --Lee Gold