Hi I just have a quick question here,

I wanted to say "it(the moon) shines", can I say "teastaíonn sí"? I don't see that usually and instead often see "tá sí ag teastáil" but the first one sounds much better in a poem I'm writing so I was wondering if it's acceptable

First off, that verb doesn't mean "shine". The verb you want is soilsigh. Secondly, the two verb forms you asked about have different purposes, as in English (though the second form exists in very few other European languages).

The first is for habitual action [which happens regularly, but is not necessarily happening right now]:
Soilsíonn an ghealach
The moon shiines
Soilsíonn sí
It shines

The second form is the "present progressive", for action which is underway right now:
Tá an ghealach ag soilsiú
The moon is shining
Tá sí ag soilsiú
It is shining

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

I am pretty sure what you were thinking of was "taitin" instead of "teastaigh"
The word "taitin" can mean both to shine and to please, which I assume is what you were thinking of instead lf "teastaigh" which just means to be wanted or to be lacking

You are correct that it is common to say "tá an ghrian/an ghealach ag taitneamh"
I have never heard "taitníonn sí" to mean she/it shines, but I wouldn't say it couldn't be right.

Of course "soilsiú" is correct as indicated above. But I am thinking you meant to ask about taitin/taitneamh

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ЯГОН ТОҶИК НЕСТ ИНҶО???

Yes sorry, I must have been alseep while writing my post, I meant 'taitin'.

Sorry as Cúmhaí pointed out I made a mistake. I meant "taitin" instead. Would it be acceptable to say "taitníonn sí" for "it shines"?

Yes, taitín would also work. I should have realized that was what you were going for. The grammatical situation is the same as for soilsigh, except that the verbal noun is different (see below).

Taitníonn an ghealach
The moon shiines
Taitníonn sí
It shines

The second form is the "present progressive", for action which is underway right now:
Tá an ghealach ag taitneamh
The moon is shining
Tá sí ag taitneamh
It is shining

_________________
I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

grma