Genesis 1:14
​14.  And God said, LET THERE BE LIGHTS in the firmament of the heaven to divide the day from the night; AND LET THEM BE FOR SIGNS, AND SEASONS, AND DAYS, AND YEARS 

The Sun Moon Stars was created on the on the 4th day.

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Genesis 1:15. And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.
16 And God MADE TWO GREAT LIGHTS; the greater light to rule the day, AND THE LESSER LIGHT TO RULE THE NIGHT: he made the STARS also. 17. And God set them in the firmament of the heaven to give light upon the earth, 18. And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.
19. And the evening and the morning were THE FOURTH DAY.

​These Scripture lets us understand a couple of things, (1st) The Weekly Sabbath is not dictated by the New Moon or else we would have been told to count seven days from the creation of it. (2nd) the Sun, Moon and Stars are synced to the Seasons.  

Genesis 8:22. While the earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.

The Most High is the Author of Time

Although Esau; (The So Called White) Changeth times and Laws he can't change what The Most High ordained how the elements of the heaven work and man can't influence them. Daniel 2:20. Daniel answered and said, Blessed be the name of God for ever and ever: for wisdom and might are his: 21. And he changeth the times and the seasons: he removeth kings, and setteth up kings: he giveth wisdom unto the wise, and knowledge to them that know understanding: 

Job 38:30. The waters are hid as with a stone, and the face of the deep is frozen. meaning its set. 31. Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion? 32. Canst thou bring forth Mazzaroth in his season? or canst thou guide Arcturus with his sons? 33. Knowest thou the ordinances of heaven? canst thou set the dominion thereof in the earth? 

No, The seasons are in place so by the changing of one these principles will cause error in the  

How To Calculate: The High Holy Days

The seasons are set in place, So by the changing of one these principles will cause error in the the timing of the High Holy Days. Which in Israel were important because of crops for offerings that took place in certain times of the year.  All Praises with have The Christ who took the physical sacrifices and transcended them to spiritual sacrifices. 1 Peter 2:5. Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ. However that does not mean we don't keep the High Holy Days but we celebrate them in the faith of Christ 

1 Corinthians 5:8. Therefore it is our duty to rehearse the righteous acts given to our forefathers. Ecclesiasticus Chapter 33: 7. Why doth one day excel another, when as all the light of every day in the year is of the sun? By the knowledge of the Lord they were distinguished: and he altered seasons and feasts. Some of them hath he made high days, and hallowed them, and some of them hath he made ordinary days. 

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Counting by the New Moon 

Genesis 1:17. And God set them in the firmament of the heaven to give light upon the earth,
18 And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.
19 And the evening and the morning WERE THE FOURTH DAY.
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The New Moon is Celebrated from Even to Even 
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1 Samuel 20:24-27 King James Version (KJV) 24 So David hid himself in the field: AND WHEN THE NEW MOON WAS COME, the king sat him down to eat meat. 25 And the king sat upon his seat, as at other times, even upon a seat by the wall: and Jonathan arose, and Abner sat by Saul's side, and David's place was empty.
26 Nevertheless Saul spake not any thing that day: for he thought, Something hath befallen him, he is not clean; surely he is not clean. 27 AND IT CAME TO PASS ON THE MORROW, WHICH WAS THE SECOND DAY OF THE MONTH, that David's place was empty: and Saul said unto Jonathan his son, Wherefore cometh not the son of Jesse to meat, neither yesterday, nor to day?
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The New Moon Was Kept On The First Day Of The Month

 

Psalm 81:3. Blow up the trumpet in the new moon, IN THE TIME APPOINTED, on our solemn feast day.

Moon Also Means Month

 

In What Time Did The Most High Appoint This Solemn Feast Day?
​Psalm 81:4 For this was a statute for Israel, and a law of the God of Jacob.
5 THIS HE ORDAINED IN JOSEPH for a testimony, WHEN HE WENT OUT THROUGH THE LAND OF EGYPT: WHERE I HEARD A LANGUAGE THAT I UNDERSTOOD NOT. 
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This Solemn Feast Day Was Ordained When Israel Came Out Of Egypt. Which was Passover the Middle of the Month (Not the First Day)

The word used is kece' which means Full moon. That's when it was ordained.  
Leviticus 23:5. In the fourteenth day of the first month at even is the LORD'S Passover. 6. And on the fifteenth day of the same month is the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread.​

Numbers 33:3 AND THEY DEPARTED FROM RAMESES IN THE FIRST MONTH, ON THE FIFTTEENTH DAY OF THE FIRST MONTH; on the morrow AFTER THE PASSOVER the children of ISRAEL WENT OUT with an high hand in the sight of all the Egyptians.
​Israel Departed From Egypt on The The Fifteenth Day Of The First Month.
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Ecclesiasticus Chapter 43:6 He made the moon also to serve in her Season for a declaration of times, and a sign of the world.
7 From the moon is the sign of Feasts, a light that Decreaseth in her perfection. ( Perfection means maximum brightness )
8 THE MONTH IS CALLED AFTER HER NAME, INCREASING wonderfully in her changing, being an instrument of the armies above, shining in the firmament of heaven;

 

The Moon Increases back to its perfect state then begins to Decrease and RENEW THE LIGHT to perfect brightness AGAIN  

Exodus 13:10. Thou shalt therefore keep this ordinance in his season from year to year.