Moon enters 'magnified' eclipse in N America

[Judi Lynn]

Sunday, June 27, 2010
Moon enters 'magnified' eclipse in N America

BBC Online

A partial lunar eclipse now under way should appear magnified to viewers in North America by an effect known as the "moon illusion".

The eclipse began at 1017 GMT, when the Moon entered the shadow of Earth, and is due to last around three hours.

Because of the timing, the eclipse is not visible from the UK or Europe.

But in many parts of the US and Canada, the eclipse should appear larger because it occurs while the Moon is so close to the horizon.

According to Nasa, low-hanging Moons look "unnaturally large when they beam through trees, buildings and other foreground objects". The reason for this is not understood

More:
http://www.thedailystar.net/newDesign/news-details.php?nid=144350

[Xithras]

1. What kind of bollocks is that?

"According to Nasa, low-hanging Moons look "unnaturally large when they beam through trees, buildings and other foreground objects". The reason for this is not understood"

Who did the Daily Star interview at NASA? The janitor?

The reason for the apparent change in size is well understood. It's an optical illusion created by the lack of visual distance cues when the sun and moon are high overhead.

[RC]

2. It it is an optical illusion, then how do cameras capture the illusion?

Actually it is the atmosphere acting as a magnifying lens. It doesn't matter if there is nothing between you and the horizon or if there are trees, buildings, etc. The apparent size is not an optical illusion. If it were trees and buildings, etc., then the effect could still be seen when the moon high overhead when looking through trees and near-by buildings. It's not.

[HiFructosePronSyrup]

3. Because cameras capture the visual clues?

http://en.wikipedia.org/wiki/Moon_illusion

Welcome to post-4th century B.C.

[RC]

4. Done this...

"Photographs of the Moon at different elevations also show that its size remains the same.

A simple way of demonstrating that the effect is an illusion is to hold a small object (say, 1/4 inch wide) at arm's length (25 inches) with one eye closed, positioning it next to the seemingly large Moon. When the Moon is higher in the sky, positioning the same object near the Moon reveals that there is no change in size."

Not true. I used a dime. I could see the moon around the dim when low, but not when the moon was higher.

[HiFructosePronSyrup]

5. Then you did it wrong.

[joshcryer]

6. I agree with HiFructosePronSyrup here. You very likely did it wrong.

While the moon does get bigger or smaller depending on perigee or apogee, it's not likely to be noticed at arms length with a dime. If you can reproduce your experiment, try using a ruler and walking out some distance between a dime taped on a window. Stand in the exact same spot (squatting or whatever to align with the moon).

No doubt it is an amazingly glorious illusion, but really the moon doesn't get magnified by the atmosphere.

Anyway, perigee-apogee:

[lazarus]

8. the method I used

was with an unfolded paperclip. I pinched the ends together to match the width of the moon at the horizon. Later, at a much higher point, the clip was still exactly the width of the moon.

[caraher]

7. Another way to burst the moon illusion...

I understand that if you look at the moon through your legs (i.e. turn your back to the moon and bend over, so you're looking back at it between your legs) that also makes it seem its normal size again.

[joshcryer]

9. Do you have pictures of yourself performing this experiment?

:D