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Why does the moon phase vary from what it should look like?

Doccot

By Doccot
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Doccot

Doccot

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Hi everyone, just joined and know very little about astronomy, but one thing is confusing me. I have an app for the moon phases, distance from earth, illumination etc which is set to my current position, yet sometimes the view on the app and other on-line lunar phase maps seem to be out by many degrees. Last night 12/01/12 at approx 22.00hrs the shadow across the moon occupied the upper right segment of the moon and not the pictured waning Gibbons from top to bottom (sorry about the description). Does anyone know why this is? I know other people around the globe have reported similar anomilies since early last year.:icon_scratch:

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Parus major

Parus major

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Ah, the youtube "sumthings wrong with the moon" thing.

The moon is litten by the sun so the light comes from the sun so if the moon is in the sky but it's dark then the sun is below the horizon so the crescent is downwards towards the sun.

Youtube people think that because the terminator is always pictured in diagrams as being on a strict N/S line the it would show like that in the sky.

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ollypenrice

ollypenrice

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The easiest way to get things clear in your mind is to put a white ball in the middle of the kitchen table and shine a fixed torch on it. Whan you walk around the moon-ball you will see its phases. Once this is clear in your mind you'll have no trouble with the real moon.

As for tha angle at which it appears in the sky, that depends on your latitude. It will seem upside down at the south pole to anyone used to looking at it from the north pole and at the equator both pole dwellers will feel it is lying down.

Olly

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Nova

Nova

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Hi and welcome. I don't think your question was "why does the moon have phases?" But you want to know why what you seeing does not match what your app is telling you. I can only assume either you have the location wrong or the programming of the app is wrong. I don't think its the moon that's wrong :icon_scratch:

Of course I suppose it could be part of the build up to the end of the world in december perhaps?

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Doccot

Doccot

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The easiest way to get things clear in your mind is to put a white ball in the middle of the kitchen table and shine a fixed torch on it. Whan you walk around the moon-ball you will see its phases. Once this is clear in your mind you'll have no trouble with the real moon.

As for tha angle at which it appears in the sky, that depends on your latitude. It will seem upside down at the south pole to anyone used to looking at it from the north pole and at the equator both pole dwellers will feel it is lying down.

Olly

Hi there, thanks for your quick response. I understand how the moons own shadow is cast over it's own surface relative to the position of the sun. The app I have is live and set to my current location (Derby UK) and displays the exact image I should see. At 22.00hrs last night the app was displaying a north/south lunar shadow, but in fact, the moons shadow was deffinitely north easterly, but this morning at 08.00 it was back to how the app displayed it. Does the shadow move differently over the moons surface over a 10 hour period?

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Parus major

Parus major

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Hi there, thanks for your quick response. I understand how the moons own shadow is cast over it's own surface relative to the position of the sun. The app I have is live and set to my current location (Derby UK) and displays the exact image I should see. At 22.00hrs last night the app was displaying a north/south lunar shadow, but in fact, the moons shadow was deffinitely north easterly, but this morning at 08.00 it was back to how the app displayed it. Does the shadow move differently over the moons surface over a 10 hour period?

No, it doesn't.

What does happen is the shadow is on the opposite side of the moon to where the sun is so if the moon in is n the sky and the sun below the horizon, ie it's dark outside, then the light side will be facing towards the ground.

If the shadow line was "up/down" on the moon the the moon would never be out at night since the sun would need to be horazontally in line with it.

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Smug Puppy

Smug Puppy

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Hi all,

I too have just joined these forums today and am the brother of Doccot (the better looking one :icon_scratch:).

I also witnessed this 'oddity' with the moon at 22:00hrs last night and have been discussing it with my brother since then. My brother decided to join this forum to see if we could get a clear answer on this matter without all the "we're going to die/Nibiru" cr*p that comes up on youtube if you search for answers there. After all, who better to answer our questions than "Stargazers" :D

Anyway, just to clarify and be completely clear on this matter, at 22:00hrs last night (12/02/2012), according to my borther's app and numerous online moon related resources, my brother (in Derby, UK) and myself (in Burton on Trent, UK...10 miles from my brother's location) should have seen the moon like this relative to our position on Earth:

A Waning Gibbous

moon1.jpg

However, what we saw was exactly like this (excuse my crude self made shadow):

moon2.jpg

However, in the morning around 08:00hrs it was back to what it should look like (the first image of the Waning Gibbous).

So, if someone could explain this for us it would be greatly appreciated.

Cheers! :(

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Spackbackle

Spackbackle

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Hey All,

I think in short the apps are wrong!

Currently it's a waining moon, As the moon rises we should see the shadow across the moon, Similar to the second picture above, as the earth rotates and we move towards sun rise our perspective of the moon changes so that we see the shadow move into a more vertical position.

I imagine that why so many apps shows the incorrect image is that they have used the same information for the programming of the app.

Edit **** Or the App is designed to show you the phase of the moon but not what you actually see with the naked eye! But I think Doccot said his app is supposed to show you what you would see! ****

does this make sense?? :icon_scratch:

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Doccot

Doccot

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Basically, it's the sun that lights that side of the moon, if the sun is below the horizon then that's the direction of the light. Tomorrow morning about 9am if you look you'll see that the lit side faces the sun.

have a play with stellarium, free software Stellarium and you'll see.

Thank you so much, that makes perfect sense. Look forward to future chats.

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Doccot

Doccot

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Hey All,

I think in short the apps are wrong!

Currently it's a waining moon, As the moon rises we should see the shadow across the moon, Similar to the second picture above, as the earth rotates and we move towards sun rise our perspective of the moon changes so that we see the shadow move into a more vertical position.

I imagine that why so many apps shows the incorrect image is that they have used the same information for the programming of the app.

Edit **** Or the App is designed to show you the phase of the moon but not what you actually see with the naked eye! But I think Doccot said his app is supposed to show you what you would see! ****

does this make sense?? :icon_scratch:

Yes it does, thank you. I'll delete the c--p app.

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Smug Puppy

Smug Puppy

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Basically, it's the sun that lights that side of the moon, if the sun is below the horizon then that's the direction of the light. Tomorrow morning about 9am if you look you'll see that the lit side faces the sun.

have a play with stellarium, free software Stellarium and you'll see.

Thanks for the link Parus. Downloaded and installed, turned date and time back to last night and you're right! Not that you will be surprised by that :icon_scratch:

It's so much easier to visualise it with Stellarium. It is exactly what we saw and how the sunrise affects what we see makes it so much easier to comprehend. I understood what you were saying previous to this, but all I could think about was the vast distance between the sun and the moon and it shouldn't make a difference to the shadow on the moon...and it doesn't....it's the way the earth rotates that changes what we see of the lit area of the moon and angle that we see it.

Anyway, that's that cleared up. Thank you all! Now, what about Nibiru! (joking :D)

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