Insisting the month can't begin until the New Moon is spotted is perilously close to moon worship!
Leviticus 23: 23 ADONAI said to Moshe, 24 "Tell the people of Isra'el, 'In the seventh month, the first of the month is to be for you a day of complete rest for remembering, a holy convocation announced with blasts on the shofar. 25 Do not do any kind of ordinary work, and bring an offering made by fire to ADONAI.'"
Ancient translations of Psalm 81:3 do not have full moon mentioned in this verse. The fact remains that we are commanded to blow the shofar at the new moon but not necessarily "sight" the new moon. The Hebrew word shomer means to "guard, keep or take count of" (Genesis 26:5). It can only indirectly mean "to observe." Furthermore, if the crescent could not be sighted we still have to blow the shofar while the moon is astronomically new; that is to say, while in darkness.
Psalm 81: 3 Blow the trumpets in the new moon in the time appointed on our solemn feast day. (Lamsa Aramaic reading.)
Psalm 81: 3 Blow the trumpet at the new moon, in the glorious day of your feast. (Psalm 81:3, LXX, Lance Brenton translation)
But the fact remains nevertheless that there is not one Biblical example of sighting the crescent as a forward looking marker
of "newness". Instead, when we look at one of the main meanings of "new"
above, we find clear evidence that its state begins in darkness:
You have heard; look at all this. And you, will you not make it known? I proclaim to you new (chadash) things from this time, even hidden things which you have not known. They are created now and not long ago;
and before today you have not heard them, So that you will not say,
Behold, I knew them. (Isaiah 48:6-7 (Matara))
So here we see clearly that "new" means "hidden, unknown things". If we then see evidence of it, like a crescent sliver, then it isn't "new" anymore!
Here's another example:
Behold, the previous things have come to pass. Now I declare
new (chadash)) things. Before they spring forth I declare them to you. (Isaiah 42:9 (Matara))
Now we have two additional details: First, something is "new" before
it springs forth. Again, wouldn't a crescent then be the precise form of
"springing forth" that indicates a lack of newness? Second, it says the old
things, "have come to pass" which in Hebrew really means, "gone away".
This is why the lunar month actually ends with the conjunction, at the time that
it has literally "gone away"! For that reason Isaiah can't help believing that
the same applies to the whole cosmos:
For behold, I create new (Chadash) heavens and a new (Chadash) earth and the previous things will not be remembered or come to mind. (Isaiah 65:17 (Matara))
The reason why the former things are not remembered is again, because they are gone. Even here though Isaiah is not finished with defining "new" and
linking it across the board:
For just as the new (chadash) heavens and the new (chadash) earth which I make will endure before Me, declares YHWH, So your offspring and your name will endure. And it shall be from new moon (chodesh) to new moon (chodesh) and from sabbath to sabbath that all mankind will come to bow down before Me," says YHWH. (Isaiah 66:22-23 (Matara))
The imagery could not be clearer. When dealing with a brand new month, the new heavens and earth follow the same pattern as the "new
things", starting from before they spring forth into the physical world! At a
minimum this "strong suggestion" demands that said definition be taken into
serious consideration rather than just cast aside for some "crescent rolls"!
Finally, notice Yahweh didn't say, "The new month begins when you actually sight the new moon; He said, "The FIRST DAY of the month"....Regardless of where you're living, clocks and calendars are a huge help! We all know the 1st day of the month because we are intelligent enough to have determined it, in relation to the Moon.
Yahweh says these things are for "signs, seasons, days, and years". (Genesis 1:14). And he said the sun (larger light) and the moon (samller) light were to rule over the day and night. (Genesis 1:16-17). Notice He never said the moon determined the precise beginning of the month! It is a sign of the new month, yes, but is not and should not be elevated to a role for which it was not created.
The bottom line is: Yahweh doesn't want us bickering over these things; He simply wants us to obey the command to keep His Feasts! We'll know who was right and who was wrong about the timing of the feasts once we're out of our "earth suits." Nowhere are we told that we will not be allowed into Heaven if we failed to keep His feasts perfectly!