Giant Moon Rising

Thursday night I was driving down the road around 10pm when I suddenly saw an amazing sight. Just visible through a gap in the trees, the largest full moon I can ever recall seeing was rising into the sky. Normally you look at the Moon and it is a relatively small looking object in the sky almost the size of a ten cent coin.

(Click to Enlarge)

On Thursday night, the Moon was easily much larger than that and was orange in color. I raced home as fast as I could and took some digital pictures which I will add to the site if they come out ok. But the question is, why was the Moon so large in appearance? Had it suddenly got close to Earth without us knowing about it?

Well I probably answered the question in the last paragraph when I used the words ” …large in appearance.”…… because that was all it was ……an optical illusion.

So I decided to look into it a little more and looked at why the moon was orange. I dismissed one suggestion I saw which stated that the orange color was due to a lunar eclipse with the light reflecting off Mars. The truth is that the Moon is that color is due to the refraction of light as it passes through the thick atmosphere. This is the same effect you see when the Sun changes color when setting and is often assited by pollution in the sky or even ash from volcanic eruptions.

When I saw the giant orange moon it was still only about 17 degrees above the horizon so it made sense that the color was due to refraction. I then suddenly realised that at no time have I ever seen an orange Moon high in the sky….. only near the horizon.

(Click to Enlarge)

Now with the size of the moon we are dealing with what is know as a Moon Illusion. This is nothing more than our brains falling for an optical illusion where the moon looks larger near the horizon than it does high in the sky. This is because you have objects like trees and buildings to compare the size of the moon to. Because you know the moon is large, you suddenly see it as large. Some people believe the Moon to be double it’s normal size but on average it’s size increases by 50 to 75%.

You can try a little experiment to prove it is an optical illusion. Next time you see a giant moon, hold up a 10 cent coin next to the Moon and note the comparison in size. Then later when the Moon is higher in the sky and has apparently shrunk in size, hold the coin up next to the moon again and you will see there has been no change.

Just an illusion all that time….well except for the color.

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~ by sydneystargazers on December 4, 2009.

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