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[bobdrake12]

http://www.space.com...s_020903-2.html





The Moon looks bigger on the horizon because the air acts like a lens, magnifying it (excerpts)




When on the horizon, the Moon appears
huge and flat from space, too.


Almost everyone has seen the Moon, red and swollen, looming hugely as it rises over the horizon. A few hours later, when it's high in the sky, it has shrunk considerably, looking more "normal." Most people are also aware the Sun exhibits this behavior, and even constellations do, too.

It's true that the Earth's air is thicker near the horizon. When you look up, you are looking through the thinnest part of the atmosphere, and the closer you look toward the horizon, the more air you look through.

However, the air actually compresses the Moon's image, instead of magnifying it. Have you noticed that the Moon looks noticeably squashed when it's right on the horizon? That's because the varying thickness of the air near the horizon distorts the Moon's shape, making it smaller top-to-bottom.

It turns out this effect of the Moon looking larger near the horizon, called the Moon Illusion, really is an illusion. You can see this for yourself, by comparing the rising Moon's size with some household object (say, the tip of a pencil eraser held at arm's length), and then wait a few hours and do it again. You'll find the size hasn't changed appreciably.

This illusion is convincing, but it's not real.





What's going on here is that your brain is interpreting the sky as being farther away near the horizon, and closer near the zenith (directly overhead). This isn't surprising; look at the sky on a cloudy day and the clouds overhead may be a few kilometers above you, but near the horizon they might be hundreds of kilometers away. The Moon, when it's on the horizon, is interpreted by your brain as being farther away. Since it's the same apparent size as when it's high up, your brain figures it must be physically bigger. Otherwise, the distance would make it look smaller.


© 2002 SPACE.com, Inc.

[bobdrake12]

http://www.space.com...s_020903-3.html





Seasons are caused by the Earth's distance from the Sun (excerpts)


On a cold winter's evening, you can huddle near a fire for warmth. If you get too close it can burn you, and if you are too far away it can hardly warm you at all. Clearly, the amount of warmth you get from something hot depends on its distance.

And hey, the Earth's orbit is an ellipse! So sometimes it's closer to the Sun, sometimes farther away. This must be why we have seasons, right?

Wrong. If you do the math, you'll find that the Earth should only be a few degrees warmer when it is at perihelion (closest to the Sun) than when it's at aphelion (farthest from the Sun). Yet the difference between summer and winter in most locations is a lot more than just a few degrees.




The real reason for the seasons is the tilt of the Earth. Ever notice that a globe of the Earth is always tilted? That's because the Earth's spin axis (the line connecting the north and south poles) is tilted to the plane of the Earth's orbit around the Sun. The amount of the tilt is about 23.5 degrees.

In the summer, the Earth's axis is pointed toward the Sun (well, not exactly at the Sun, but in that direction). When that happens, the Sun gets higher in the sky. Its light is more concentrated, and it heats the ground more efficiently. Also, days are longer, giving it more time to heat things up. Summers are hot.

In the winter, when the Earth's axis is directed away from the Sun, the Sun is lower in the sky. The light hits the ground slanted, spreading it out. That makes it heat things a lot less efficiently. Days are also shorter, giving it less time to heat things up. Winters are cold.

That's why the opposite hemispheres have opposite seasons, too. When the Northern Hemisphere of the Earth is tipped toward the Sun, the southern one is tipped away, and vice-versa.


© 2002 SPACE.com, Inc

[chubtoad]

Balancing eggs on equinox
It doesn't matter you can balance eggs just as well on any day of the year.