Does my plot point centered around eclipses make sense?

Question

My main antagonist is an infant Great One that's been imprisoned below the Moon's surface and I want its influence and physical form to have a weakness to direct sunlight which, I think, gives me a reason to make eclipses more than just a pretty event.

Here's my logic: A long-dead organization cast a 'magic' spell that created a planet-wide barrier that severely inhibits the Great One's psionic/arcane/cosmic/spiritual/whatever influence through it. The catch, is that this barrier has a city-sized, funnel-shaped 'eye' or pinhole, anchored to the ritual site from whence it was cast (Central United States), through which the Great One can periodically poke its figurative tentacle. However, direct sunlight has a harmful effect on the little abomination so it remains inside its prison which, itself, has an extremely narrow view-hole through which the {eye of the barrier} can be seen. Like a pencil-thin shaft a football field long or something. Only when this tiny opening in the prison and the 'eye' of the barrier align well enough, can it exert its will on the surface of the planet in full force. Incidentally, I think this can only happen during lunar eclipses and total solar eclipses and even then, only when they coincide with the region of the barrier's ritual.

{Partial illumination of the moon, like that seen during a lunar eclipse will not deter the Great One's influence and its view-hole (or even multiple view-holes) can be anywhere it/they need(s) to be on the moons's surface to make this idea work. As long as direct sunlight crosses the path between the view-hole(s) and the barrier's eye, the influence will be disrupted.}

{I can change the angle or topography of the funnel shape or even give it a relatively small amount of motion around the anchor site, if necessary.}

A couple things I've thought of that support this idea's validity:

1.) Yes, the Moon is tidally locked to the Earth, but I don't think this means the Moon would be at a good enough angle to align the barrier's eye and the Great One's peephole {every time it's visible in the sky}. If I understand my research, a blood moon or total solar eclipse would be the time the Earth and Moon are closest to zenith in the sky above their respective surface {which I imagine would be the only range of positions in the sky that align the view-hole(s) and the barrier's eye}.

2.) What about the full Moon? Too much direct sunlight.

3.) New moon? Depends on the angle.

EDIT: I've clarified and added details, marked with {}, to the above text in response to an answer by Dalila.

Answer 1

The key to this whole thing is, in fact, the geometry of the funnel, the 'viewing' angle that it provides. Of particular importance is how much of the Earth can be 'seen' through it at any one time.

The second most important factor is just how much sunlight is too much. Neither solar nor lunar eclipses achieve 'complete' darkness on Earth's surface or the Moon's, so unless there is leeway given for partial darkness, then there is no alignment or arrangement that will allow influence to escape.

For simplicity, I'll narrow down the geometric range options to just 'wide angle', meaning the full surface of the Earth is 'visible' through the funnel, and 'narrow angle', meaning that only a portion of the Earth's surface can be 'seen'. Just how narrow is 'narrow' can be adjusted as needed for the story.

The possible lighting limitations are solar eclipse, lunar eclipse, and new moon.

Combining the angle options with the lighting options gives six possible alignment situations:

1. wide angle + solar eclipse
2. wide angle + lunar eclipse
3. wide angle + new moon
4. narrow angle + solar eclipse
5. narrow angle + lunar eclipse
6. narrow angle + new moon

So, lets address each one:

1. For this option, the Moon's surface (the important part) will certainly be dark enough. This option also assumes that the area of totality is also dark enough. And the area of totality will certainly be visible, since the whole surface is visible. So the limiting factor will be how often the path of totality passes over the hole in the barrier. Any eclipse with a path of totality that passes over the hole will provide an opportunity for influence.

2. For this option, the whole of the Earth's surface will certainly be dark enough. This option also assumes that the whole of the lunar surface (the important part) is also dark enough. The limiting factor will be when the hole in the barrier is on the dark side of the Earth during the eclipse (about half of all of this type of eclipse, since the hole will be on the light side half of the time, and the dark side half of the time). So about half of all lunar eclipses will provide opportunity for influence. Though it will almost certainly NOT be alternating opportunities, but rather relatively long sequences of opportunities followed by relatively long sequences of eclipses with no opportunity.

3. For this option, the important part of the moon's surface will always be dark enough. A 'complete' new moon is practically never visible from a completely dark area of Earth's surface, but a very near new moon is visible from almost every area of the dark side of the Earth at some point during the night. If no leeway is given for partial illumination, even when the important areas are in near complete darkness, Then this rules out new moon completely as a possibility for influence. But it would also eliminate both types of eclipses, and lock the influence completely and permanently. To avoid that, it must be assumed that partial illumination of the surfaces is allowed, and that assumption opens the floodgate to allow influence any time even just the opening of the funnel is in darkness while the hole in the barrier is also in darkness and facing the moon. That would be many times per month, for significant durations for many of the instances. This seems significantly (prohibitively?) more than the 'once per special eclipse at special times' implied by your original question, so, to me, that seems to rule out all possibility of the "wide angle" options, in any form.

4. For this option, the moons surface is certainly dark enough. Assuming partial darkness is enough, the path of totality is also dark enough. Since the whole surface of the Earth is not 'visible', the visible area of the Earth is a limiting factor. The path of totality passing over the hole in the barrier is another limiting factor. So influence would ONLY be possible when the path of totality crosses the hole in the barrier AND the hole in the barrier is visible from the funnel AT THE SAME TIME.

5. For this option, the surface of the Earth is certainly dark enough. Assuming partial darkness is enough, the surface of the moon will also be dark enough. The hole in the barrier would need to be on the dark side of the Earth, but that will be relatively common compared to how often it's in the path of totality of a solar eclipse, so while it's a limiting factor, it's a minor one. The main limiting factor (assuming the hole in the barrier is in darkness) will be if the hole can be 'seen' from the funnel during the eclipse.

6. As with option 3, complete darkness on both important sides of the surfaces will practically never happen in these cases, so near complete will have to be allowed. Again, as with option 3, partial darkness will happen quite often, during lunar cycles, and earth day cycles. But as the completeness of the darkness increases, the probability of aligning the funnel and hole in the barrier decreases, which is exactly the opposite effect from eclipses. This alignment requirement would be so drastic that they would VERY rarely, if ever, align (I suspect they would never align) to allow influence, unless the alignment was intentionally (by the story teller, not the 'spell casters') set up to allow for influence at new moons, instead of eclipses.

(TLDR) In summary:

A wide viewing angle should be avoided, unless you want influence on a monthly bases, for days at a time. If you want eclipses to be the main thing, then New Moon's won't be. If eclipses are the thing, Lunar Eclipses are the more likely to cause influence because of how much of the important side of Earth's surface is dark during them.