“O, swear not by the moon, the inconstant moon”

You know… ever since February started, I have had the strangest feeling that it was the wrong day.

Ever have that?

Get out your red pens.

Each day I turn another page of my copy of the Martyrologium Romanum, which is always out on a book stand. Today I received a note from a scholarly reader about a problem with the MartRom!

A google search for “Martyrologium Romanum” brings up several of your posts, and it seems as if you might use the newest edition (2004) regularly. I’d just like to alert you to a misprinting of the lunar calendar tables for February that I just noticed. I apologize if the following isn’t entirely clear, as it is tougher to explain than to see.

If you happen to read the day of the month you’d likely notice it
Monday anyways. For the 23rd, under “k” is 4, and for the 24th, “k” is 6, which means of course that something is wrong. It seems that the error traces back to the table for February 5th. [the culprit!] For this year the (ecclesiastical) new moon (“k”=1) is given as the 20th, while the correct date is the 19th.

So, for 5 februarii – 23 februarii, the table of the moon is a day off, for letter “E” on the 5th, and an additional letter (to the left) each day through the 23rd. On 24 februarii, the error is corrected and each incorrect letter is adjusted forward 2 days. O(null)n these days, wherever the number “30” is inscribed, read “1”, and adjust the following numbers though “E” accordingly. I just have the effected years bracketed in pencil to remind me to make the adjustment.

This error is unfortunately repeated exactly in the Italian

(One other obvious error I’ve found in the moon tables is that on 20 ianuarii, the table printed is totally incorrect, as it is a repeat of the 13 ianuarii table.)

I hope you find this useful and are able to pass it along if others ask about it. I was seriously perplexed until I tracked down how the February new moon was off this year! (Last year (“N”), the error didn’t have any effect, thankfully.)

It seems that the Moon is calculating, harsh mistress that she is.

BTW… it was the lunar New Year the other day for people in China and Vietnam and a few other places.

And, speaking of things lunar, don’t forget the great conjunction!  HERE

About Fr. John Zuhlsdorf

Fr. Z is the guy who runs this blog. o{]:¬)
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  1. Nicholas says:

    Speaking of Lunar New Year, our bishop has offered a transference of this past Wednesday’s and Friday’s obligation of fasting and abstinence forward in honor of the new year.

    Therefore, I say:

    Happy Tet!!!

  2. James says:

    Where might I find a copy of the Martyrologium Romanum? The 2004 edition doesn’t seem to be available in any of the usual places (Amazon, Abe Books, ebay, etc.)

  3. The Masked Chicken says:

    Versions are available, on-line. See the bottom of the following link:


    The Chicken

  4. Gregorius says:

    If it’s not too much trouble, would Father vel alii explain how to read those charts? The most common English translation (sold by Angelus Press) does not use them, and my Latin is not quite up to snuff when I tried to read the instructions in the original.

  5. Andrew says:

    The Martyrologium is a liturgical book. It is prayed: ideally chanted. It starts with the day announced in Latin (I have no idea how this is handled in the vernacular) according to the Roman custom, as for example for the 23d of Febrary: Septimo Kalendas martii. This is followed by the announcement of the Lunar day, as for example: Luna quarta. The entire sequence goes like this: Septimo Kalendas martii Luna quarta Anno Domini MMXV. Then (I think) follows the narrative depicting the given Saint.
    There are tables that guide you to the right letter under which you will find the Lunar day. The entire subject of Solar vs. Lunar Calendar is complex and a good place to start exploring it might be here:


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