Why does the sun appear to be bigger at sunrise and sunset than at midday?
Same question also applies to the moon?

informer wrote:
Why does the sun appear to be bigger at sunrise and sunset than at
midday?
Same question also applies to the moon?

Curvature of the Earth's atmosphere.
The atmosphere can bend light, like drops of water
There are other variables here as well, like the thickness of the air

The thicker the air, the more it's bent

Example:

sun on the horizon
the light from the bottom part of the sun is travelling through more
air than the top part. The air bends the light up towards the top half,
giving the sun a squashed appearance

a setting sun looks normal horizontally but becomes more vertically
challenged.

The sun can also appears different colours at sunrise and sunset, hence
the sometimes striking photographs we can get. The effect is amplified
when there's more stuff in the air. After volcanic eruptions, there can
be some very striking sunrises and sunsets

The Moon appears about two to three times larger when on the horizon
compared with overhead

In the case of the Moon Illusion no-one knows excatly.
positively it's known to be an illusion, because of the way our brains
interpret images. It's a question for psychologists rather than weather
science.

Some of the factors involved.
imagine looking at a crowded street scene. the people standing near you
appear to be larger than people further away, but we don't view the
more distant people as being much smaller in size. An effect known as
Size Constancy.

Now look up 'Ponzo Illusion' on the net - which desribes a very common
perspective effect, that can trick our brains

The shape of the sky makes the brain perceive the Moon as being farther
away on the horizon than when it's overhead.
The Ponzo Illusion demonstrates that when you have two objects of same
physical size but at different distances, the brain interprets the more
distant object as being bigger.
Our brains interpret the moon as being bigger when it's on the horizon

Also an internet search engine will give you more info

eg:
http://digbig.com/4chxg

I picked up this useful information from a book:
Bad Astronomy by Philip Plait

He's a professional astronomer

Also tackles questions such as:

Why does the sky appear blue?
Does the sun really give off a yellow colour?

"BlueLightning" wrote

Curvature of the Earth's atmosphere.
The atmosphere can bend light, like drops of water
There are other variables here as well, like the thickness of the air

The thicker the air, the more it's bent

Example:


Thanks for the info. I have been wondering about this for 20 years. I know
it wasn't really a weather question but I knew that there would be someone
here that had the answer.
Cheers!

On Fri, 24 Dec 2004 06:43:34 +0000 (UTC), "informer" wrote:

Why does the sun appear to be bigger at sunrise and sunset than at midday?
Same question also applies to the moon?


It's an optical illusion. If you actually measure the sun/moon width at sunset
or sunrise, and compare it with the measured width at midday, you will find it
is exactly the same.

Distortion of the sun and moon near the horizon is due to varying atmospheric
densities, this does not make the sun or moon look any bigger.

Martin

On 2004-12-24 08:34:20 +0000, JPG said:
On Fri, 24 Dec 2004 06:43:34 +0000 (UTC), "informer"
wrote:

Why does the sun appear to be bigger at sunrise and sunset than at midday?
Same question also applies to the moon?

It's an optical illusion. If you actually measure the sun/moon width at sunset
or sunrise, and compare it with the measured width at midday, you will find it
is exactly the same.

Distortion of the sun and moon near the horizon is due to varying atmospheric
densities, this does not make the sun or moon look any bigger.

Martin


.... although the reasons why it is an optical illusion aren't well
understood. There has been quite a debate about it in the psychological
literature. My preferred explanation is based on the fact that on the
horizon there are obviously cues that provide information about
distance; high above the horizon there are not. We think of the dome of
the sky as a flattened surface, and all the visual cues suggest that
things on the horizon at a distance must be further away then objects
at the zenith. If two objects take up the same visual angle, and one
appears to be further away, we think it must be bigger.

If you want to find out more, you could look at:

http://www.grand-illusions.com/moon.htm
http://science.nasa.gov/headlines/y2...onillusion.htm
http://facstaff.uww.edu/mccreadd/
http://www.lhup.edu/~dsimanek/3d/moonillu.htm

Some of these sites carry a health warning for psychophysical theory.

Note that not every one sees the illusion - 10% of the population are
immune to it.

Trevor
http://www.personal.dundee.ac.uk/~ta...ritweather.htm

It's an optical illusion. If you actually measure the sun/moon width at
sunset
or sunrise, and compare it with the measured width at midday, you will find
it
is exactly the same.

Distortion of the sun and moon near the horizon is due to varying atmospheric
densities, this does not make the sun or moon look any bigger.

Martin

This is all correct except for the bit about the moon being the same
size. Interestingly enough, it's actually smaller when near the horizon than
when high in the sky.
Imagine a plane through the centre of the earth at right angles to
the line joining the centres of earth and moon. Where that plane cuts the
surface of the earth the moon will be on the horizon. But if you see the moon
high in the sky you must be on that part of the earth that bulges towards the
moon, which is therefore closer to you than it was if you viewed the moon just
rising or setting. The closest you can get to the moon is when it is overhead.
The maximum value of this effect is about 1.8%. For the sun, being much
further away, the effect is negligible. In any case, all this is quite swamped
by the optical illusion we've been talking about.

Tudor Hughes, Warlingham, Surrey.

On Fri, 24 Dec 2004 06:43:34 +0000 (UTC), informer wrote:

Why does the sun appear to be bigger at sunrise and sunset than at
midday?

Google is your friend I should think but it's almost certain to be
tied in with how much atmosphere is between you and the sun.

--
Cheers
Dave. pam is missing e-mail