I was wondering if the moon was close to full moon and whether it had any connection to Lupin's heavy sleep on the train.

  • 1
    – user68762
    Nov 17, 2017 at 9:16
  • 3
    @Morrigan the issue is that the moon calendar doesn't work for the potterverse - with it, the buckbeack's execution doesn't happen during full moon.
    – Lause
    Nov 17, 2017 at 9:18
  • 19
    @Lause No calendar works for the Potterverse. Nov 17, 2017 at 14:54
  • 5
    JKR isn't very good at maths Nov 17, 2017 at 16:28

2 Answers 2


TL; DR It was a full moon IRL, but not in the Potterverse.

The Hogwarts Express leaves London on the 1st of September every year. In 1993 -Harry's third year at Hogwarts- it was a full moon IRL, as you can see in this calendar.

Since the train arrives after dusk, Professor Lupin should have turned into a wolf in front of the kids. So the moon was in a different phase in the book's universe.

It may be that J.K. Rowling forgot to check the moon calendar, or maybe she did but couldn't rewrite the chapters in a satisfying way and decided to use an alternative moon calendar for her universe.
Otherwise she would have had to find a credible reason to postpone the train's departure date for this specific year only, or remove Lupin from it, which would have completely changed the first part of the book.

The best indications we have on this alternate calendar are Lupin's transformations periods. He took his first sick leave in early November of 1993, and had a number of those during the year. The only night we know for sure was a full moon is the 6 June 1994.

There are 278 days between the two nights and 278 = 9*29.5 + 12.5
So in-universe the first of September was probably a waxing crescent moon.

I first assumed a lunar cycle of 28 days, but it's closer to 29.5 on average.

  • 5
    @Edlothiad I think you probably misunderstood the intention of my comment - if we assume that J. K. Rowling made a mistake whilst checking the moon calendar, there is evidence suggesting a possibility she was off one year.
    – Lause
    Nov 17, 2017 at 9:38
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    Ah that makes more sense. She seems to have a habit of messing up the little things, my apologies.
    – Edlothiad
    Nov 17, 2017 at 9:44
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    @Edlothiad rather than saying she has a habit of 'messing up' the little things, I would argue that she mostly doesn't care about them, preferring a compelling story over the correctness of details. That may not be the choice all of us would make (I for one would probably craft a world in obsessive detail before writing such a story and spend ages on achieving consistency across books) but it's the one she made and it seems to have worked well enough ;)
    – Cronax
    Nov 17, 2017 at 13:45
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    @Lause "if we assume that J. K. Rowling made a mistake whilst checking the moon calendar" - I think you may be making a mistake in assuming that she checked a moon calendar at all
    – David K
    Nov 17, 2017 at 14:42
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    @LookingForAName rest assured your English is excellent, as is your answer. +1
    – BlackThorn
    Nov 17, 2017 at 16:15

When the dementors attacked, it was already dark outside, so it was not full moon.
If it was full moon (or one night earlier or later), Lupin might have slept, too, but as a wolf.

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