The Moon

[George T]

Sometimes the moon looks very big when it’s low, Why?
I’ve been told that it’s because of the pollution in the atmosphere. Anyone know any better?

GMT

[Beethoven]

It is just an illusion...although it does indeed LOOK bigger it is just your brain being fooled.Objects low on the horizon look bigger and if you put your thumb out at arms-length and compare it to the moon low on the horizon (when it looks huge) and do the same later on when it is higher,you will find that it is exactly the same size in relation to your thumb...weird innit?!! Nothing to do with atmosphere though.

[Busta Level]

Hate to disagree Beet, but it is very much to do with the atmosphere!

When the sun/moon are lower on the horizon, their light has to pass through a relatively thicker portion of atmosphere to reach your eyes(due to the angle of incidence) then when they are high in the sky. This has the effect of acting rather like a lens in a magnifying glass, hence the fact that the moon appears bigger. You can also see more detail of the surface features (like looking at the moon through a weak telescope) for the same reason.

The 'pollution' in the atmosphere (which has always been around - dust, smoke etc) has the effect of making the moon/sun seem red when they are low on the horizon for the same reason. The light has to pass through (relatively) more of the atmospheric pollution, and it thus becomes more noticable.

Either way, it is a beautiful sight watching a nice sunset or moon rise!

[ 13 January 2002: Message edited by: Busta Level ]</p>

[stagger]

Hate to disagree Busta but the moon subtends about 0.5 degrees wherever it is in the sky. Have you ever tried the thumb experiment that Beethoven suggests?

It's a very famous optical illusion and pollution doesn't really have much to do with it. However, people find it hard to agree on the exact way in which the illusion works.

Have a look at this...

<a href="http://www.pnas.org/cgi/content/full/97/1/500" target="_blank">Explaining the moon illusion</a>
Kaufman L, Kaufman JH.
Proceedings of the National Academy of Sciences
Vol. 97, Issue 1, 500-505, January 4, 2000

[Beethoven]

And in fact,people have taken photos of what they thought were amazing harvest moons or wonderful sunsets (the same illusion applies to the sun) only to be disappointed that the photos are not as impressive as they thought and the moon looks the same as it always does.Possibly the reason why much more surface detail is apparent could be that the moon seems much less bright near the horizon and maybe this allows us to see more...I am not sure though.Try going to <a href="http://www.google.co.uk" target="_blank">www.google.co.uk</a> and typing in "Moon Illusion"..there is loads on the web about it and lots of other interesting illusions too.

On a similar note,does anybody remember seeing the moon a few months bach when it was reportedly at its brightest for years...nearly burned my eyes out..it was like looking at a bulb!!

[Busta Level]

I stand corrected! Amazing what you learn on the 'net. It's only taken me 30 odd years to find that one out :)

I'll try the thumb thing next time I see the full moon <img src="wink.gif" border="0">

[George T]

Nice one. Thanks a lot <img src="smile.gif" border="0">

GMT

[A Very Civil Pilot]

Also when the moon is low in the horizon, you have something to compare the size to, so it looks big compared to the skyline. At its zenith there is not alot out there, and it looks a bit lost in all that space.

[OnTheStep]

apropos, if you turn your back to the moon while it's near the horizon, bend over and look at it upside down between your legs, it will appear the same size that you're used to seeing it.

sounds rather barbie but we all know you'll be walking to your car in the parking lot some day and try it out! (under the guise of picking up a dropped pen of course)

.....and i know you're wondering, so suffice to say that it's something an astronomy prof bestowed on us many moons ago

[ShyTorque]

If you try that experiment with no trousers on - you could get a friend to make a comparison! :)

[OnTheStep]

^^^i didn't say i condone it lol

i'd just as sooner take someones' word for it