# Seeing a half Moon - where is the Sun?

• B
A little off subject, but a few years ago I went out fishing just as the sun was rising. Perfect morning, not a cloud in the sky. The moon at this stage, was still clearly visible and both the moon and the entire sun were sharing the same sky. Which is pretty cool but what to this day makes me question reality is the fact that the sun was directly behind me and the moon was directly infront of me and yet I could only see half the moon. How does that happen?

timmdeeg
Gold Member
A little off subject, but a few years ago I went out fishing just as the sun was rising. Perfect morning, not a cloud in the sky. The moon at this stage, was still clearly visible and both the moon and the entire sun were sharing the same sky. Which is pretty cool but what to this day makes me question reality is the fact that the sun was directly behind me and the moon was directly infront of me and yet I could only see half the moon. How does that happen?
This is really off topic and perhaps my answer will be removed.

To see the full moon requires that moon, earth and sun are almost on a straight line which happens to be at sunset. If the sun is just behind you that isn't sufficient, the angle between moon, you and sun wasn't close to 180°.

Tayler
This is really off topic and perhaps my answer will be removed.

To see the full moon requires that moon, earth and sun are almost on a straight line which happens to be at sunset. If the sun is just behind you that isn't sufficient, the angle between moon, you and sun wasn't close to 180°.
It sure looked close enough, and even if it wasn't bang on 180°, less the half the moon was showing?

I don't know. However, you mentioned fishing, so there was a big body of cool water and you also mentioned the sun rising, which means the air was being heated faster in some places.

So, there could be some refraction happening. Were you on the water? Was the moon also suffering some aberration due to refraction? Maybe the real alignment of the sun and moon wasn't as close to 180 degrees as it appeared.

davenn and Tayler
Staff Emeritus
This sounds impossible. You are in a line between the sun and the moon, and the sun is not in line with you and the moon. I don't think so.

Can you give us the date?

davenn, sophiecentaur, russ_watters and 1 other person
Drakkith
Staff Emeritus
Which is pretty cool but what to this day makes me question reality is the fact that the sun was directly behind me and the moon was directly infront of me and yet I could only see half the moon. How does that happen?
I suspect that the Moon was still pretty far above the horizon and not a perfect half-moon. We humans are very poor at judging distances, angles, and other such things with any real precision.

sophiecentaur, russ_watters and Tayler
I suspect that the Moon was still pretty far above the horizon and not a perfect half-moon. We humans are very poor at judging distances, angles, and other such things with any real precision.
Thats the only excuse I can think of. Must be the size and distance of the sun and moon from where I was viewing them that give me this sort of "illusion".

This sounds impossible. You are in a line between the sun and the moon, and the sun is not in line with you and the moon. I don't think so.

Can you give us the date?
That would be very hard to remember an exact date but if I do a bit of thinking I could get pretty close. It looked fake. Like a glitch in the matrix
I don't know. However, you mentioned fishing, so there was a big body of cool water and you also mentioned the sun rising, which means the air was being heated faster in some places.

So, there could be some refraction happening. Were you on the water? Was the moon also suffering some aberration due to refraction? Maybe the real alignment of the sun and moon wasn't as close to 180 degrees as it appeared.
Yeah, I was in the boat 3 kms out from the shore.

Do you mean like a change in colour? If so no. It just looked like it was fake. This is what actually made me so fascinated by space

russ_watters
Mentor
A little off subject, but a few years ago I went out fishing just as the sun was rising. Perfect morning, not a cloud in the sky. The moon at this stage, was still clearly visible and both the moon and the entire sun were sharing the same sky. Which is pretty cool but what to this day makes me question reality is the fact that the sun was directly behind me and the moon was directly infront of me and yet I could only see half the moon. How does that happen?
You should try to re-create this scene with two pieces of fruit and a flashlight.

The simple explanation is that the sun and moon were both higher than you think.

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You should try to re-create this scene with two pieces of fruit and a flashlight.

The simple explanation is that the sun and moon were both higher than you think.
Yeah I did that and it lights up the whole face of the object, indicating I should have seen a full moon? Maybe if I try again, but to more precise scale.

..Concerning refraction....Do you mean like a change in colour?
Not quite. I meant that light rays are bent when they pass from a region of low density to a region of high density.

Taken from Wikipedia: https://en.wikipedia.org/wiki/Refraction

Hence, different air densities could make the sun and moon appear lower than they actually were.
There are many visual distortions that are common with atmospheric refraction, for example the sun is often said to look flatter. Various things could have worked together to create something that "looked fake", as you described.

Soldiers chase after Oasis that they see of the middle in the desert, although it is usually just a refracted image of the blue sky that they are seeing on the ground.

davenn and Tayler
Not quite. I meant that light rays are bent when they pass from a region of low density to a region of high density.

View attachment 283403

Thanks for helping me understand. I can see what you mean and that could be a factor.

sophiecentaur
Gold Member
2020 Award
Refraction is another matter but, if you want to be sure that the Sun, Moon and you are in a straight line, the Moon should coincide with the shadow of your head (eye). If your shadow is not pretty close to the Moon then you weren't seeing a half moon. Contrast could be very poor in the daytime too.

Those two images are seven days apart so the accuracy with which you could assess how near the left hand (half Moon) condition will be limited. Just one day out could mean 12 degree error, or so.

Drakkith and Tayler
Notice that the dark side of the moon shouldn't be dark.

sophiecentaur
Gold Member
2020 Award
Notice that the dark side of the moon shouldn't be dark.

Perhaps your shadow should be to your left? Memory can play tricks. (Artwork, definitely a C-, I'm afraid. ) Both you and the Moon should be illuminated from the same side. I think it should be the apparent height of the shadow of your head that should be the same as the Moon's elevation. Both Sun and Moon should be low in the sky. Details of atmospheric refraction are only worth following up when you have sorted the basics.
I like @russ_watters suggestion of trying a model with a flashlight and a basket ball - a good, directional light, in a dark room.
Any time you can go out and see the Moon, you can rely on the Sun being in a line, just above the centre of the illuminated bit of the Moon. If there's a lot of Moon illuminated then the Sun will be below the horizon but what you see makes sense. In the mid evening, the Sun will be a bit further North of where it set and the Moon's appearance will verify that - get your ball and flashlight outside and do the two things in parallel. (Ignore strange comments from passers by!!)
One other thing you can do is to look at the Moon when it is at 'half moon' stage (look at a lunar calendar on line). At around 1800 local time, it should be at its highest in the sky. The Sun may or may not be visible, depending on the time of year.

Maybe I've just spent to much time overthinking it but yes ill definitely have a play around with some balls im sure that won't look strange haha

sophiecentaur
Gold Member
2020 Award
Maybe I've just spent to much time overthinking it but yes ill definitely have a play around with some balls im sure that won't look strange haha
You'll need to have a story ready!

Tayler
Drakkith
Staff Emeritus