The Naked Scientists

The Naked Scientists Forum

Author Topic: Why the brightness of full moon's center and edge look the same?  (Read 3025 times)

Offline jccc

  • Hero Member
  • *****
  • Posts: 990
    • View Profile
Super moon tonight, watch it for a while, awesome view in the sky, queen of the heavens. She is my g/f.

Then the question hits me. Help!



« Last Edit: 14/07/2014 02:09:23 by jccc »


 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8134
  • Thanked: 53 times
    • View Profile
The full-moon disc appears uniformly bright because it has an irregular surface: it is not billiard-ball smooth.

Mountains at the centre of the disc are viewed from above,

Mountains at the edge of the disc are seen side-on which reflect more light ...



Counteracting the fall-off in light-intensity towards the edge that would occur on a smooth sphere.
« Last Edit: 13/07/2014 11:19:24 by RD »
 

Offline jccc

  • Hero Member
  • *****
  • Posts: 990
    • View Profile
The full-moon disc appears uniformly bright because it has an irregular surface: it is not billiard-ball smooth.

Mountains at the centre of the disc are viewed from above,

Mountains at the edge of the disc are seen side-on which reflect more light ...



Counteracting the fall-off in light-intensity towards the edge that would occur on a smooth sphere.
Thanks a lot!

A basketball has more irregular surface than the moon, seems the edge looks darker under flash light?
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8134
  • Thanked: 53 times
    • View Profile
A basketball has more irregular surface than the moon, seems the edge looks darker under flash light?

Is the flash-light "sun" placed at 40,000 baseball-diameters from the baseball ?

If the  flash-light "sun" is close to the ball there will be more noticeable fall-off in brightness due to the increased distance the light has to travel to the edge , (~ the radius of the ball, which is more significant than you may think due to the Inverse square law ).

 

Offline jccc

  • Hero Member
  • *****
  • Posts: 990
    • View Profile
A basketball has more irregular surface than the moon, seems the edge looks darker under flash light?

Is the flash-light "sun" placed at 40,000 baseball-diameters from the baseball ?

If the  flash-light "sun" is close to the ball there will be more noticeable fall-off in brightness due to the increased distance the light has to travel to the edge , (~ the radius of the ball, which is more significant than you may think due to the Inverse square law ).
I double tested, you nailed it.

Thanks again!
 

Offline dlorde

  • Neilep Level Member
  • ******
  • Posts: 1441
  • Thanked: 9 times
  • ex human-biologist & software developer
    • View Profile
I double tested, you nailed it.

Excellent - someone who's prepared to test the claim - top marks!

In fact, top marks for the whole thread.
 

Offline jccc

  • Hero Member
  • *****
  • Posts: 990
    • View Profile
I double tested, you nailed it.

Excellent - someone who's prepared to test the claim - top marks!

In fact, top marks for the whole thread.

Give me a N prize please!
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Also note, there is essentially no atmosphere on the moon to interact with the reflection of light. 

When we view the moon, it is illuminated by essentially a single source of light (the sun). 

When you look at a ball or sphere in the daylight, you see the effect of the sun on one side, and ambient light on other sides, and thus see the whole side of the ball, with different light sources illuminating different parts.

Looking at the moon, the section not illuminated by the sun is very dark, and thus giving the partial lunar shapes (crescents). 

You could probably stimulate this with a basket ball and flash light in a dark room, and looking at the basket ball from different directions. 

One other issue would be the paint you choose to put on your sphere.  A glossy paint will tend to reflect more at an angle in line with the source.  Thus one would expect one area to appear brighter.  A flat paint, on the other hand, would reflect light in essentially all directions, and any point on the sphere would reflect the same amount of light to the observer. 

The moon, of course, has more of the flat omnidirectional reflection properties.
 

Offline jccc

  • Hero Member
  • *****
  • Posts: 990
    • View Profile
Appreciate for the detailng!
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums