<blockquote>
<p>With a first quarter Moon I notice that in the evening the Moon is lit from the east and the following morning the opposite limb west is illuminated.</p>
</blockquote>
<p>Actually, the <em>same limb</em> is illuminated.</p>
<p>If you could photograph the Moon in the evening and again in the morning and compare the two images carefully and recognize a few features, you'd be able to verify for yourself that the same geographic area of the Moon was illuminated both times.</p>
<p>What's happening is that you are using your own local horizon as a reference, and from your perspective the moon &quot;flipped over&quot; overnight.</p>
<p>Imagine holding a crescent moon paper cut-out near the west horizon, with the bottom edge bright, then slowly moving it down towards the ground and up again towards the east.</p>
<p>At all times the bright edge will be leading the motion, and will now be on the top side in the East.</p>
<p>In this ~12 hours the real 3D relationship with the Sun will change a little but not much. It's just that your view of the Moon has flipped.</p>

CC BY-SA 4.0
2023-01-15T22:53:52.730Z
2023-01-15T22:53:52.730Z
uhoh
<p>With a first quarter Moon I notice that in the evening the Moon is lit from the east and the following morning the opposite limb west is illuminated. I understand that my position has changed by 180 degrees in the 12 hours but surely that would not account for the change in appearance entirely as the suns position in relation to the Moon has not changed?</p>

CC BY-SA 4.0
2023-01-15T17:47:49.793Z
Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Community
CC BY-SA 4.0
2023-01-15T20:51:55.907Z
A first quarter moon is not visible in the morning. It doesn't rise until about midday and sets at midnight.  Please experiment with Stellarium or something similar to see how the moon is lit from your location at different times.  A third quarter half moon is lit on the other side, but that is because the moon has orbited 180 degrees around the Earth .
James K
<observational-astronomy>
Half Moon illumination evening and morning
NoelC
# Half Moon illumination evening and morning

(Asked by: username_0 on 2023-01-15)

With a first quarter Moon I notice that in the evening the Moon is lit from the east and the following morning the opposite limb west is illuminated. I understand that my position has changed by 180 degrees in the 12 hours but surely that would not account for the change in appearance entirely as the suns position in relation to the Moon has not changed?

**Tags:** observational-astronomy

> **Comments:**
> **username_1**: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.  
> **username_2**: A first quarter moon is not visible in the morning. It doesn't rise until about midday and sets at midnight.  Please experiment with Stellarium or something similar to see how the moon is lit from your location at different times.  A third quarter half moon is lit on the other side, but that is because the moon has orbited 180 degrees around the Earth .  

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## 1 answers

### Answer by username_3 on 2023-01-15. Score: 1

> With a first quarter Moon I notice that in the evening the Moon is lit from the east and the following morning the opposite limb west is illuminated.

Actually, the *same limb* is illuminated.

If you could photograph the Moon in the evening and again in the morning and compare the two images carefully and recognize a few features, you'd be able to verify for yourself that the same geographic area of the Moon was illuminated both times.

What's happening is that you are using your own local horizon as a reference, and from your perspective the moon "flipped over" overnight.

Imagine holding a crescent moon paper cut-out near the west horizon, with the bottom edge bright, then slowly moving it down towards the ground and up again towards the east.

At all times the bright edge will be leading the motion, and will now be on the top side in the East.

In this ~12 hours the real 3D relationship with the Sun will change a little but not much. It's just that your view of the Moon has flipped.


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