View Full Version : H2O/Mako Moonpools are wrong

08-10-2015, 12:29 PM
We just discussed this in the "Happy"-thread, and I feel the need to spread awareness about it :D

Strangely enough, I never paid much attention to the detail in mermaid shows that the full moon will always wander directly overhead to shine into the moonpool.

Now, my astronomical lessons are sadly lacking, but this is simply not possible unless you are at the equator.
(Neither Mako nor the Scottish cave where Bella turned is situated at the equator.)

The moon is always in a different position every night, and apart from the equator, never overhead.
The highest it gets is during the winter solstice in the northern hemisphere, and vice versa for the southerners.

How the Moon can be shining into water in reality:

Floodlight, aka Fake:

the word "moonpool" originally describes a subterranean lake that comes up to the surface inside a cave.
It's also used for artificial subaquatic access to the water (i.e., a "pool" situated underwater in a cave, drilling station, submarine...)

08-12-2015, 12:38 PM
Hi Echidna,

There is actually a band of latitudes around the equator where the moon passes overhead.

The key comes from the inclination of the earth's axis of rotation (23.4) and the angle of the plane of the moon's orbit around the earth relative to the plane of the earth's orbit around the sun (5.1) The moon's peak height varies in a complex manner, but it can pass directly overhead over the band from 28.5N to 28.5S, with increasingly low frequency the further north or south one goes.

This means that the moon can pass directly overhead in Australia as far south as Gold Coast in Queensland (28S) but it will happen very rarely. There is no way the moon will ever pass overhead in Scotland.

FWIW, when I was living very near the equator as a kid, the moon often went straight overhead. The last time I was in India I stayed in a city at 10N of the equator, and the moon happened to go overhead too. (Yikes! This sounds so nerdy reading it back. Does anyone else track the moon? I have an app on my computer that tells you all the information about the current or future state of the moon when you click on it. http://www.smileysnetwork.com/anges/ange04.gif)

08-12-2015, 02:51 PM
Hey Aptamer!

Yes, I totally worded that wrong.
I meant near the equator.

This is what Merman Chatfish said about it in the thread I mentioned:

In order for the moon to ever be directly overhead you would need to between 22 N and 22 S latitude. At the equator you would have two times per year the moon was directly over head. At 22 only once.

If you are at 22 South, the sun and moon will be highest Jan 21/22. At my location in Iowa (Wolfram alpha is being a brat) the sun never gets higher than 77 above the horizon (Jun 21/22 since I am in the northern hemisphere).

Now lets take a look at what days Jan 22 has a full moon. Between 1900 and 2100 there are 8 times: 1913, 1924, 1970, 2008, 2027, 2046, 2065, and 2084. I don't know how long their mermaids live, but in human terms, the winter solstice and a full moon will only happen 5 time while I am alive.

He also found these amazing links, which I promptly bookmarked and played around with:

And I found out I must have been very close to an overhead moon when in Egypt one time.
I saw Far North QL is very close to the range indeed, but Gold Coast is much farther down.

At any rate, I don't get how I never wondered about the "moon passes directly overhead and over the volcano cone every month" while watching the mermaid shows.

Merman Dan
08-12-2015, 03:33 PM
Perhaps the light of the moon is reflected through a lava tube coated in a mirror-light substance?
On a side note... Blue Grotto (http://www.capri.net/en/s/la-grotta-azzurra)!!

Azurin Luna
08-12-2015, 04:11 PM
I went to a blue grotto in Curacao, it was really cool... except for the loud tourist group...
For us it was the sunlight that was reflected from the white sand at the bottom of the grotto, but I bet the moon can do the same, though less bright.