A number of people seem to be convinced that the Sabbath (Hebrew: Shabbat) cycle must be based on the cycle of the moon, rather than repeating seven day weeks. The lunar Sabbath theory seems to be driven by the fact that most of the other appointed times (Hebrew: mo’edim) such as Pesach, Chag HaMatzot, Yom Teruah, Yom HaKippurim and Sukkot are all set on specific days of specific months.Lunar Sabbath proponents hold that the first day of the new month is “New Moon Day”, (a rest day but not a Sabbath), and the weekly cycle for the month begins on the second day of the month. This makes the 8th, 15th, 22nd and 29th days of the month the Sabbath rest days. This type of Sabbath cycle has the Sabbath falling on different days of our modern Julian calendar week each month. One month the Sabbaths might all begin on Tuesday while the following month they begin on Thursday.
It’s relative easy to show that this theory does not stand up to scrutiny.
It’s not all about the moon!
Lunar Sabbath proponents argue that the appointed times, including the Sabbath, are all supposed to operate on a lunar schedule, and one of the passages they like to refer to comes from Psalms 104:
He made the moon to mark the months, and the sun sets according to a regular schedule.Psalms 104:19
The NET here has taken some liberty. The hebrew behind “the months” above is actually “mo’edim” which means appointed times, and thus this verse becomes the “proof” of a lunar Sabbath cycle to those who believe in such.
However, a psalm is poetry/song, not instruction (nor in my opinion are the post-Torah Judaean writings inspired or authoritative). For actual instruction or details needed to understand something, one should look in the Torah. This description of the luminaries from Genesis 1:14 is very instructive:
God said, “Let there be lights in the expanse of the sky to separate the day from the night, and let them be signs to indicate seasons and days and years,Genesis 1:14
Genesis 1:14 is not solely about the moon. The “lights in the expanse of the sky” include the moon, our sun, and the suns of other systems (stars). Further, they are not only for indicating seasons (moedim), but also days and years. There is simply nothing about this verse that is exclusively lunar for determining seasons, days or years.
Presentation of the Mo’edim in Leviticus 23 supports the weekly shabbat cycle
When one reads through the presentation of all the appointed times in Leviticus 23, one finds that all of them except for the Sabbath and Feast of Weeks (Hebrew: Shavuot) are set on specific days of the month. The reason this is not the case for the Sabbath and Feast of Weeks? 1) The Sabbath is based on a weekly cycle and will not be on the same day each month, and 2) the Feast of Weeks is anchored to the Sabbath and also ends up on different days of the month each year!
With the lunar sabbath cycle, Sabbaths are on the same four days every month, which would likewise put Shavuot on the same day of the same month each year. If this was the case, these moedim could and would have been presented the same way as the others.
We fix dates to months even on the solar Julian calendar!
The fact that most of the mo’edim are fixed to a certain date of a certain month don’t make them unique to a lunar calendar. This is the case in our predominant Julian calendar today as well. Your birthday is the same day of the same month every year, for example, even though the Julian calendar is solar.
Six days of work followed by a day of rest
Six days work may be done, but on the seventh day there must be a Sabbath of complete rest, a holy assembly. You must not do any work; it is a Sabbath to YHWH in all the places where you live.Leviticus 23:3 NET
Lunar Sabbath proponents believe the first day of the month is a new moon day (on which no work is done) and then the six work days begin. My question is: why continue a weekly cycle for the rest of the month? If the Sabbath is determined by counting six work days after the new moon day, what possible reason is there to assume that the weekly cycle, which is not lunar at all, continues for a second, third and fourth week (plus an extra day sometimes)? It is not logical to constrain the identification of the first monthly Sabbath to the new moon, and then infer that the weekly cycle continues throughout the month from there. When you see that the lunar sabbath is impossible given the instructions for Shavuot, clearly this idea of working six days and resting the seventh represents the recurring weekly cycle.
Final proof from the details of the Feast of Weeks (Shavuot)
The details of Shavuot really put this issue to rest definitively:
You must count for yourselves seven weeks from the day after the Sabbath, from the day you bring the wave offering sheaf; they must be complete weeks. You must count fifty days – until the day after the seventh Sabbath – and then you must present a new grain offering to YHWH.Leviticus 23:15-16
It is common for english translations to render Shabbatot (Sabbaths), the plural of Shabbat as weeks. However, there is a word for weeks: Shavuot. Weeks are not actually mentioned in the above verse at all. These instructions indicate that the count to Shavuot begins on the day after the first Sabbath, and ends after counting 50 days to the day after the seventh Sabbath. This 50 day count crosses two month boundaries. With the lunar cycle injecting days into the weekly cycle (two new moon days at least and probably at least one other day given that the lunar cycle is 29-30 days each month) it is impossible for the 50 days count to begin on the day after the first sabbath and end the day after the seventh sabbath in the lunar Sabbath cycle.
Hopefully this helps clear up any confusion of this issue. The lunar Sabbath cycle is simply not supported by scripture. The biblical calendar is both lunar AND solar. The first month of the year is always in the spring. This requires an extra month to be added to the calendar some years, making the cycle of yearly moedim sometimes 12, sometimes 13 months apart. That is not strictly lunar, but lunar/solar.
I do suspect that the lunar and solar cycles were aligned originally. See this article for more details.