From: nguyenpd@ntmtv.UUCP (Phat Nguyen)
Subject: ANSEWER TO WHY TEHE SUN LOOKS BIG
Originator: nguyenpd@nmtvs315
Reply-To: nguyenpd@ntmtv.UUCP (Phat Nguyen)
Organization: Northern Telecom Inc, Mountain View, CA
Date: Thu, 27 Aug 1992 20:37:08 GMT

> trinh@twix.etdesg.TRW.COM (Tien Trinh) writes:
> Xin cha`o ca'c anh chi.
> 
> Co' ai bie^'t ta.i sao the sun ra^'t to khi mo.c vao` buo^?i sa'ng va`
> la.(n va`o buo^?i chie^`u. va` nho? vao` lu'c tru+a???????
> TT
>
> C.N.M.T writes:
> Ca^u tra? lo+`i cu~ng -do+n gia?n tho^i : the magnifying effect of
> moisture in the air is LESS during noon than during dawn or sunset
> thus the sun seems smaller.

> Su+. a^?m u+o+'t trong ba^`u khi' quye^?n (moisture in the air) "acts 
> just like a giant magnifier glass".  Lu'c ban tru+a, su+. a^?m u+o+'t
> -da~ tan bo+'t ne^n ba^`u khi' quye^?n ma^'t da^`n su+. pho'ng -da.i
> cu?a no' (the magnifying effect lessens when there is less moisture
> in the air) cho ne^n mi`nh nhi`n tha^'y ma(.t tro+`i co' ve? nho? ho+n
> lu'c tru+a .
>
> Lu'c ban sa'ng, ba^`u khi' quye^?n co`n la.nh ne^n nhie^`u su+. a^?m 
> u+o+'t va` lu'c chie^`u khi tra'i -da^'t quay qua^'t da^`n bo'ng ma(.t
> tro+`i, ba^`u kho^ng khi' nguo^.i da^`n (cool down) va` su+. a^?m u+o+'t
> trong ba^`u khi' quye^?n ta(ng da^`n.  Vi` the^' khi mi`nh nhi`n ma(.t 
> tro+`i lu'c ban sa'ng hay ban chie^`u, ma(.t tro+`i co' ve? to ho+n vi`
> nhie^`u moisture in the air.
>
> Yeah,
> 
>    it's because the sun is farther in the morning and in the evening than in the afternoon.
> 
> What???  When the Sun is FURTHER away in the morning and in the evening then
> it is BIGGER??  And it is SMALLER when it is CLOSER???  Do you drink too
> much coffee this morning???  :-)) ;^)) :-))


C.N.M.T is only partially right.  His answer is a good guess but it
has not quite the correct one.  It doesn't explain why the same 'hien
tuong' also occurs to the moon.  The moon always looks much bigger
when it is at the horizon than when it is at the top.  If C.N.M.T 
is right, then it will never happen to the moon because the light
reflects from the moon is not that great to heat up the 'bau khi
quyen'.   In fact, at midnight it tends to be colder and more moisture
in the air than at any other times. Here is my explanations:

This 'hien tuong' happens because our eyes have been fooled by our
inability to judge the right distance.  When the moon or the sun
is at the top, our eyes can perceive the correct distance because
we are looking at them at a straight line and we know that they
are far away and we take into account this fact.  In addition,
there is nothing that stays in our view that makes us interpret
things differently.  We can correctly judge the right distance
between the earth and the sun, so the sun and moon looks small
to us.  On the other hand, when the moon and the sun are at the
horizon, we cannot judge the right distance and we assume that
the sun and the moon are much closer to us.  So we interpret that
they must be much closer, so they look bigger.  Why does this
phenomenon occur?  Because when they are at the horizon, we can
only see at most 60 miles from where we stand.  In addition, there
are other things such as mountain, the surface of the earth, the
surface of the water, houses, trees and these things are really
really close to us in term of the distance between the earth and
the sun.  And it seems to us that the sun or the moon is just
behind these houses and trees.  So unconsciously, we assume that
the sun and the moon must be very close to us.  Because we think
that they are close, our brain interpret them as bigger.  The
magnifying effect is very very small compared to our own interpretation
of the relative distance between the earth and the moon.  So it
says to us that things are not really the way they are, it is
our own brain that tends to distort things.  In fact, some
people use this theory to fool the eyes.  I have seen some 3D
pictures using this technique even though the pictures are 2D
themselves.  For more info on this phenomenon, refer to the
researches in THE PSYCHOLOGY OF PERCEPTION.  I happened to
take this class before and I have tested out all of their
experiments including some of them that shows how to make
the moon looks small when it is at the horizon (they do this
by looking at the moon reflected from the glass holding at
45 degree angle.)  Their techniques really work, if you don't
believe it, you can check out some books on the psychology
of perception and do the experiments yourself.  So I get
the right answer, is there any 'Pho?' for me?????


Nguye^~n Doa~n Pha't
Northern Telecom
Mountain View