question abt moon

desmond_lim87 · Post by **desmond_lim87** » Sun Aug 22, 2004 11:19 am

Hi.. experts out there.. i hav a question abt the moon.
Yesterday night (21/08/04) abt 11pm.. i saw a waning moon.. tis is a veri special moon which i nver seen b4.. tis waning moon is orange-red in colour and the size is 2 times the moon that i everyday's moon.. is it that the moon is closer to earth? but y is it orange-red colour.. tnkZ

Desmond

fizzy123 · Post by **fizzy123** » Sun Aug 22, 2004 11:35 am

I not sure but I think bcos, the water vapor in atmosphere cause different degree of diffraction.Perhaps when moon at higher altitiude less light traverse thus no orange color.

8)

ChaosKnight · Post by **ChaosKnight** » Sun Aug 22, 2004 1:32 pm

Let me guess. The moon you saw was low in the horizon right?

anat · Post by **anat** » Sun Aug 22, 2004 3:28 pm

I think what you saw is called "earthshine". The red-color light in the dark area is reflected from the earth to the moon. It is in red because the other wavelengths are dispersed by earth atmosphere. BTW, the size is the illusion when you compare to the surrounding.

shoelevy · Post by **shoelevy** » Sun Aug 22, 2004 8:24 pm

yeah
anat is correct
the enlarged size is an illusion because your brain compares it with closer stuff like buildings.

the red colour of the moon is similar to a red sunrise, when a celestial object is low, the light passes through more atmosphere and red light is dispersed hence making the object look red. its true for all objects, moon, sun, stars and even planets. earthshine or the illum part of the moon, the same concept applies

Sam Lee · Post by **Sam Lee** » Sun Aug 22, 2004 9:00 pm

If i'm not wrong, when a celestial objects is low down the horizon, the thick atmosphere tends to act like a magnifying glass (refraction of light), therefore any object, including our moon, will appears to be enlarged when its near the horizon. This also explain why we see the constellation Orion (and our Sun) larger when its near the horizon.

Regards,
Sam

Post by **Airconvent** » Mon Aug 23, 2004 12:52 am

Sam Lee wrote:If i'm not wrong, when a celestial objects is low down the horizon, the thick atmosphere tends to act like a magnifying glass (refraction of light), therefore any object, including our moon, will appears to be enlarged when its near the horizon. This also explain why we see the constellation Orion (and our Sun) larger when its near the horizon.

Regards,
Sam

If it did, I doubt it magnify that much to be significant. The moon appears larger due to it being compared with objects in the horizon such as flats, trees, etc. One way to be sure is if you see the moon at the horizon, lock on to its size and imagine the same moon now at zenith. you'll be surprised to note that the size apparently looks the same!

rich

MooEy · Post by **MooEy** » Mon Aug 23, 2004 7:24 am

perspective la, our eyes is like a wide angle lens, it distorts perspective. hold a piece of card near ur eye and look at an object far away from u, the card looks way bigger than that object. now move that card slowly away from ur eyes, it will start to look smaller and smaller.

the human is incapable of measuring size, often we just compare an object to another to tell the size. the moon is extremely far away from us, and if u use buildings or other things to compare the size, perspective will come in. if u stand closer to a building, the moon will appear smaller, but if u stand further away, the moon will appear slighty bigger.

a more accurate way of estimating the size of the moon would be extending ur arm straight, then use ur hand, see how many fingers it takes.

~MooEy~

Kamikazer · Post by **Kamikazer** » Mon Aug 23, 2004 9:11 am

i saw the moon near zenith at 3pm yesterday...
or did i see wrongly?

the moon looks larger at zenith than near the horizon as it is nearer to us at zenith and further away (by 1 earth radius) near the horizon...?

Post by **weixing** » Mon Aug 23, 2004 10:01 am

Hi,

i saw the moon near zenith at 3pm yesterday...
or did i see wrongly?

You didn't see wrongly... The moon was around zenith at 3pm yesterday.

the moon looks larger at zenith than near the horizon as it is nearer to us at zenith and further away (by 1 earth radius) near the horizon...?

I tell you what, do as Mooey mention, extending your arm straight and use your last finger (or the small finger) to cover the moon. Do the same when the moon is lower on the horizon. You should discover that the size of the moon is actually the same... your last finger will just cover the moon no matter where the moon is, Zenith or Horizon.

By the way, your last finger will cover 0.5 degree of the sky at an arm distance.

Have a nice day.