Psalm 81:4 (or 81:3, depending on version)
ד תִּקְעוּ בַחֹדֶשׁ שׁוֹפָר; בַּכֵּסֶה, לְיוֹם חַגֵּנוּ. 4
The word "keseh, or kasah"(כֵּסֶה) means "cover, covered" or "hide, hidden". I found the word "keseh, or kasah"(כֵּסֶה) in the Tanak 154 times using E-Sword. I took the time to read it in every verse. Not once does it ever mean "Full Moon" or "fullness". Every single time this word is used, in all 154 uses, it means "cover, covered", or "hide, hidden". Consider these verses:
Gen 7:19 covered=כֵּסֶה
The mountains are completely covered, or hidden.
Gen 7:20 covered=כֵּסֶה
Gen 9:23 covered=כֵּסֶה
Noah was covered.
Gen 18:17 hide=כֵּסֶה
In this verse, כֵּסֶה is something hidden.
Gen 24:65 covered=כֵּסֶה
Rebekah covered herself with a vail. This is probably a thin cloth that completely covered the face. Not the half-vail that only covers the mouth. The same word for vail is used by Tamar to decieve Judah. This type of vail probably looked like a burka.
Gen 37:26 conceal=כֵּסֶה
To keep the murder a secret.
Gen 38:14 covered=כֵּסֶה
Same meaning as 24:65.
Gen 38:15 covered=כֵּסֶה
Same thing here too.
It always means the same thing. Covered or hidden.
This is just in Genesis. The word is used the same way all throughout the Tanak.
Lebana is the correct word for "Full Moon". So I believe Psalm 81 has nothing to do with a Full Moon.
This is how I translate it:
Blow the shofar on the New Moon. When the Moon is hidden, on the day of our Feast.
The word "hidden" is כֵּסֶה.
The verse is referring to Trumpets(Yom Teruah). But it also shows that the New Moon is hidden.
According to this Psalm, the New Moon is not a crescent. A crescent is obviously visible, while the adjective כֵּסֶה is something that can't be seen, as the verses above prove.
This is the only time in the whole Bible, out of 154 times כֵּסֶה is used, that it is mistranslated as "fullness" or "Full Moon". Why?
It appears that this verse is purposely mistranslated to try and hide this obvious reference to the New Moon being dark, instead of a visible crescent.
No where is the New Moon called a crescent in the Bible. There is a word for crescent, but it has nothing to do with a New Moon. It is used to refer to jewelry or ornaments.
The connection between Yom Teruah and the hidden New Moon is that Yom Teruah represents the second coming of Yahshua. A secret, unknown day. Joel 3:15-16 tells of the day of YHWH as a day of darkness. YHWH will roar as a lion. This is a reference to Yahshua returning, symbolized by a lion. He is the lion of the tribe of Judah. Matthew 24:29-30 also tells of a dark Moon during this time. Yahshua also said He would return secretly, as a thief in the night. So a hidden Moon represents His coming very well.
Darkness is the beginning of time in Genesis 1:2. Before light was created, there was darkness. Darkness begins the day at sunset. We don't wait for sunrise to begin Shabbat. Shabbat begins at sunset, just like every day from the very beginning of time. In the same way, the New Moon begins in darkness. The end of the Moon cycle is also it's beginning. As soon as the Moon is completely dark, it begins to grow again. This beginning of growth is the New Moon. Just as we are hidden in the womb and too small to see with the eye, so too is the New Moon. Just because we can't see it with our feeble eyes doesn't mean it isn't there. It is there, and it is growing.
The day on which the Moon becomes visible again depends on too many things. Such as the weather, a person's vision, location, altitude, and how much of the sky is visible or obstructed by mountains or other things. So 2 people in the same town can see the Moon at different days, because one has better vision or lives higher up. There is even more of a discrepancy when people in separate towns are both looking for a crescent Moon.
The biggest problem with a crescent Moon, is that it can be cloudy for many days in a row. Sometimes for most of the year. Crescent keepers get around this problem today by using internet or phones, but that isn't how they did it back in Bible times, did they?
The word "observe" in the Bible isn't something that has to be visibly observed to be kept. This is the same thing the lunar sabbath keepers say about Shabbat. They say the only way to tell when the Sabbath is, is by visibly observing the Moon. They say the true Sabbath can't be calculated. In Ex. 31:16 the KJV has "observe the Sabbath". The word "observe" is שָׁמַר, "shamar". It means to "guard", or "protect". It's not about "looking" for something, as they believe. We are to guard the Sabbath and New Moon.
I've read both sides of the debate from history books. Some say the Jews calculated it, some, or possibly just one, mentions watchtowers and fires to signal when the crescent was sighted. I think it may have been "The Jewish Book of Why".
There may be a reason for this. I think the Jews were divided over this "dark vs. crescent" debate even in Yahshua's time.
There are verses that suggest this, such as Luke 22:8, John 18:28, and John 19:14. According to these verses, Yahshua kept Passover a day before the Priests. Yahshua had already eaten it, but it seems the Priests had not. An "Enoch" calendar keeper tried to use these verses to prove that Yahshua was keeping the "Enoch" calendar. I think it's because the Priests were crescent Moon keepers, so they kept Passover a day later than Yahshua.
1 Samuel 20:5 tells us that David knew in advance when the New Moon would be. He didn't need to look for a crescent.
If you look for the crescent, please show Biblical proof for why you do so. The above verses I provided are Biblical evidence for a dark New Moon. Any writings outside the Bible are trumped by the above verses. So please do not post "evidence" from non-Biblical sources.