The moon seen at 10 am. this morning.

[Segilla]

Why is it, when the sun is fully risen, that the moon on which it shines is not seen as a full circle?

[Segilla]

TKS. Is there somewhere I can see a diagram as I can't visualise this.

[New Judge]

I don’t normally like to simply provide a link when giving an answer. However, the phases of the moon are a bit complex to explain, even with our new limit of 4,000 characters. So this may help:

http://www.moonconnec...com/moon_phases.phtml

[gen2]

The moon is full when it is directly opposite the sun (180 degrees apart). The sun will be on one side of the earth, and the moon on the other. Since you cannot see through the earth, you will only see one or the other at any given time.

If you are seeing both in the sky at the same time, then the angle between them must be less than 180 degrees and thus the phase of the moon must be either before or after full.

[askyourgran]

The sky was very clear this morning, I watched some of the planes going over it looked as though they were almost going to land on the moon

[Segilla]

Thanks New Judge. I'll have to print out the page and study it carefully.

[Jonathan-Joe]

Segilla, why not experiment using a ball in a room with just one source of light?

[mibn2cweus]

Moon ) ======s=u=n=l=i=g=h=t====== ☼ Sun



You (^: looking up from

-^-^-^-~~ the Earth


Looking at the part of the Moon that is illuminated, you can deduce the general direction of the source of illumination, the Sun. But to infer from this the Sun's actual location you need to realise that in relation to the Moon, the Sun is very far away, nearly four hundred times beyond the orbit of the Moon. So when you see a crescent moon that is apparently not far removed from the Sun in the sky, remember it is being illuminated almost from behind, from far beyond the Moon's orbit. In fact, with respect to the Sun, the Moon and Earth are never separated by more than a small fraction of one degree of arc. Therefore, it is the angle of the Moon (not its apparent proximity) to the Sun as seen from Earth that largely determines the degree of illumination we observe -
180° = 100%
90° = 50%
45° = 25%
18° = 10%
or about 5% for each 9° of separation.

[Segilla]

Thanks for all your explanations.

[Old_Geezer]

I have always had problems visualising how the phrases come to be. Some kind of mental block I suppose. If it is night where I am, then the other side of the world has the sunlight, and the moon on our side should be all lit up. If it is only half lit up then the sun must be to the side of my world, and so it isn't night. Arrhhh ..... I think I found an animation once, that helped visualise it, but like a fool seemed not to have saved the link.

[wildwood]

Hang a ball from a tree with a string, eye hight. On a dark night stand 15ft in front of the ball and get someone to shine a torch from behind you (the sun) at the ball. Now get that person to stand at a right angle to the ball and shine the torch again. You will now only be able to see about half of the ball. Now get that person to walk in a circle back behind you while keeping the torch trained at the ball. You'll now notice ¾ and other phases of the ball (moon).