God uses months based on a lunar calendar which begin on the first sliver of the moon after a new moon. That is what the ancient new moon was; namely, when the first crescent of the moon appears that could be seen from the Mount of Olives.
Jewish calendars base their months on the modern day new moon, so they are often a day or two off from the actual biblical first day of the month. The Jews changed their calendar around 300 ACE (AD) to when the moon is dark. If God uses His festivals as signals/signs as it says in Genesis 1:14, then it is important for us to know the true and ancient first day of Jewish months.
The word “seasons” in Genesis 1:14 is the Hebrew word “moed” and actualy refers to the moedim, the festivals of God or biblical festivals. We see many prophetic things happening on the moedim, so we should look for prophetic promises to occur on God’s feasts. God’s feasts relate to what God has done, what God is doing, and what He will do. Therefore, finding the actual first day of the biblical month is important.
Click on the Below Link to See When God's feasts are for 2020.
Jewish Months 2019-2020 | Dates
The true Jewish months according to the reappearance of the Moon. The ancient new moon is when the moon reappears.
Jewish Sabbaths | Days of Rest
Jewish Sabbaths - Day of Rest
Passover - 1st day no unnecessary work
Passover - 7th day no unnecessary work
Shavuot no unnecessary work
Rosh Hashanah no unnecessary work
Yom Kippur no unnecessary work; fasting commanded
Sukkot - 1st day no unnecessary work
Shemini Atzeret - eighth day no unnecessary work
Shabbat - 7th day of week no unnecessary work
How to Find the True First Day of the Jewish Biblical Month
Only for the Nerdy:
Here’s how to find the biblical first day of the month for any month.
1) Find a resource that can tell you when nautical twilight begins. The sun during that time is 6 to 12 degrees below the horizon. That’s when three ordinary stars are visible. During civil twilight (the sun is 0 to 6 degrees below the horizon) one can only see bright stars and planets. You may also want to look at when astronomical twilight begins and ends. Also, note when the moon sets. One of those resources that has all this information is: www.timeanddate.com.
2) Find out what day the moon is first visible in Jerusalem after the modern day new moon.
3) Check to see if it will be dark enough for the moon to be seen in Jerusalem. That would be in nautical twilight as well as astronomical twilight (the sun is 12 to 16 degrees below the horizon in astronomical twilight). Seeing three ordinary stars and the first crescent of the moon is the beginning of the Jewish/biblical day. If the moon sets before nautical twilight, the moon may be visible, but three ordinary stars will not be visible.
4) The true ancient first day of the Jewish/biblical month is when the first crescent of the moon appears in nautical twilight or after before it sets.
Click to download the table I made for 2018 - click the link.