Cycle of blue moons from year 0

  1. Year 0 in some systems exists and in year 0 there is a blue moon. There are also blue moons in year 3, year 8 etc. This 4,5 I have seen so far and this makes me think that it has that 4,5,3,16,17,2,9, and then repeats at 16 cycle.

    Sites including wikipedia say that a blue moon occurs every 2 to 3 years. Well they are wrong on that.
  2. jcsd
  3. The calculation on the wikipedia page is very simple. If you have 365.23 days in a year and 29.53 days beteen full moons, you have 12.368 full moons each year, so 0.368 extra full moons each year, wich is an extra full moon every 2.71 years.

    Unfortunately I don't understand the numbers you wrote at all.

    There are 2 different definitions of a blue moon around. Either the third full moon of a season with 4 full moons, or the second full moon in a month. If you use the second definition, you can get an extra blue moon in a year with no full moon at all in februari. You'll get a blue moon in januari and march. This will happen in 2029. If you use seasons, this can't happen.
  4. I used plus a site that had year 0 and looked at each year that had a blue moon which I am using the 2nd in a month that most people use. I looked at each year that had a blue moon, subtracted from the previous year with a blue moon and got this:
    3(my mistake for putting in that 4),5,3,16,17,2,9,16,17,2,9 and so it repeats at 16

    Thus the every 2-3 years that most sites say is wrong.

    Plus unless you know blue moons have this cycle from year 0 it is unpredictable when the next one will occur and even if somebody predicts "Oh a blue moon in a particular year will occur 2 years afterwards" that would mean that from year 0 every leap year would have a blue moon and not every leap year has a blue moon so that is some evidence against a 2-3 year cycle. That plus what I have seen on calendar websites that go back to 1 AD or even further to 0 AD 0 BC and years before year 0 which they put on the calendar websites with moon phases as -x AD tells me that indeed it is the cycle of numbers that I have above.
    Last edited: Apr 25, 2014
  5. You must be doing something wrong. According to, there are blue moons in

    2013, 2016, 2019,2021, 2024, 2027, 2029, 2032 (of the 3rd full moon in a season with 4 full moons type).
    That's 7 blue moons in 19 years, or one every 2.71 years.
  6. SteamKing

    SteamKing 8,373
    Staff Emeritus
    Science Advisor
    Homework Helper

  7. I am not doing the third full moon in a season with 4 moons I am doing the 2 per month which has a much more unpredictable cycle. According to some people there is a year 0.
  8. Yeah, astronomers work with a year 0. That's not the problem

    You seem to be pulling your figures for blue moons out of thin air. The exact definition isn't that important, nor the year zero. You give figures for the dates of blue moons that are
    - incomprehensible. I don't know what "that it has that 4,5,3,16,17,2,9, and then repeats at 16 cycle" means
    - seem to have no source

    while you can't say what is wrong with the simple calculation that gives 1 blue moon in 2.71 years, and that's backed up with the actual dates of blue moons on
  9. I honestly looked at the calendar on during years with a blue moon(the 2 in a month type), subtracted that from the previous year with that same thing and got 3,5,3,16,17,2,9,16,17,2,9 repeating at 16. that is the correct cycle and the 2-3 years is the wrong cycle and it is a good source is.
  10. When I go to

    I see there's a blue moon 28-jan-0001 (2 full moons in a month)
    Year 1 is the earliest year for wich the page works.

    no blue moon


    checking up to year=22 results in:

    30-jan-0017 and 31-mar-0017 extra blue moon, because no full moon in februari

    looks like once every 2 or 3 years.
  11. I had to go to a different site for the year 0 which has a blue moon in october. But if it is every 2 years from year 0 that means that year 1 would not have a blue moon and that every leap year would and that isn't true.

    I looked at the calendar which has dates for full moon, new moon, first quarter, and third quarter and it says year 1 does not have a blue moon but another site with year 0 says that year 0 does and I find with the calendar this cycle of year differences: 3,5,3,16,17,2,9,16,17,2,9 etc.
  12. Bandersnatch

    Bandersnatch 1,200
    Gold Member

    Caters, what are you talking about? The site you cited shows the blue moon at the dates willem2 listed for you. It's clearly a 2-3 year cycle. The numbers you show make no sense.
    Maybe you could show us exactly, step by step, what calculations you're doing to get them(it's anything but clear)? You said something about subtracting something from the previous year with a blue moon - what are you subtracting exactly?
  13. No it does not show a blue moon in january of year 1.

    I am looking at the years, every single month of them, finding 1 with a blue moon, subtracting the previous year with a blue moon and getting this almost unpredictable cycle that is not 2-3 years.

    In fact with a 2-3 year cycle only a minority would have years matching with what I am doing to get this almost unpredictable cycle. Plus if it is every 2 years from year 0 all leap years will have them and if it is every 3 years than a smaller fraction of leap years will have them and a larger fraction be in the non-leap years. That is some evidence against a 2-3 year cycle because neither of those are true(well maybe the larger fraction in non-leap years but not so simple as 3rds, 4ths, or 5ths which it would be with a 3 year cycle).
    Last edited: Apr 26, 2014
  14. Bandersnatch

    Bandersnatch 1,200
    Gold Member

  15. To get my very unpredictable cycle I start at year 0 with a blue moon. I find year 3 has one as well but the calendar if you don't look at the moon phase one but the one with the days of the week showing major moon phase dates below the calendar for that month of that year it clearly shows that there is no blue moon in january of year 1.

    How I get this 3,5,3,16,17,2,9,16,17,2,9 etc cycle is I look at the calendar with the days of the week(which is supposed to be accurate in their moon phases especially full moons), see which ones I see more than 1 full moon in a month on subtract the previous year with that same thing from the year that I am looking at and get this unpredictable cycle of years between blue moons.

    You guys are looking at the moon phase calendar and the moon phase calendar and days of week calendar are contradicting. The moon phase calendar says it is every 2-3 years but the days of the week one says that it is this cycle of differences between years starting with year 0(which I needed to go to a different site for) and year 3: 3,5,3,16,7,2,9,16,17,2,9 etc.

    Year 1 moon phase calendar:
    says there is a blue moon in that year.

    Year 1 calendar with days of the week:
    This is what I look at and says there is no blue moon during that year.
  16. Bandersnatch

    Bandersnatch 1,200
    Gold Member

    Fair enough on the year 1 point. The webpage mode you're talking about does indeed lack the first full moon in January. If you look at the moon phase mode, the first full moon in jan. doesn't have the date at all. Since a quarter should take about 7 days, and the third is on the 5th, then the previous full moon should have been in late December the previous year(with a blue moon sometime in year 0).

    However, apart from this point, all the blue moon years from both modes do match. It's a 2-3 year cycle. I could post a screenshot if you want.
  17. The difference between the two, is that the year 1 calendar is using the Julian calendar prior to September 1752, and not the Gregorian calendar. The moon-phases calendar has the full moon on 13 January 0001 and the days of the week calendar on 27 January 0001

    I can't see the calender before year 1, but the first full moon in year 1 was 27 January, so there should have been a blue moon the year before. (If you go one month back in the calendar, the full moon is about 0.9 days later in the month on average, the difference in days between the average month and the average time between full moons)

    The next blue moons are July-03, May-06, December-08, August-11, June-14, January-17, November 19, July 22 etc, so you still get about 7 in 19 years.
  18. Bandersnatch

    Bandersnatch 1,200
    Gold Member

    Seriously, I'm beginning to wonder if you're being serious.
    Both use Julian calendar, as is written below each calendar mode. It's in your links in post #14. There is no full moon on 13 Jan 0001 in any mode. That's the date of new moon.
    There IS a difference between the two modes - the moon phase calendar uses UTC(GMT), the other mode lets you choose the place w/r to which the calendar is drawn. If you choose USA, or any other not-UTC time zone, there will be discrepancies of up to one day between the dates of each quarter. This can and will lead to a shift in blue moon months or years, but only slightly, and most importantly, the period between blue moons will have remained the same 2.7 years.

    It's all written in plain text on the website. If you can't see this then I can't help you any more.

    Edit: terribly sorry. I thought I was talking to caters. Do be kind enough and disregard the jaded bits, both of you.
    The rest still stands, though.
    Last edited: Apr 27, 2014
    shows full moons for UTC, with a full moon on 28 Jan at 00:44
    shows a full moon in the US on 27 Jan (time not specified because there are several US time zones)
    28 Jan 00:44 UTC corresponds to 27 Jan 19:44 EST
    The 'first' full moon of Jan (UTC) [per] may be spurious as the third quarter moon for Jan falls on 5 Jan, but it should be *7* days after a full moon.
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