# Glaring astronomy mistakes in a movie or video **URL:** \ **Category:** Cafe Society\ **Tags:** movies\ **Created:** [September 5, 2026, 8:39pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849 "2026-09-05T20:39:34Z")\ **Posts on this page:** 9\ **Page:** 10
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 14, 2026, 10:01pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/181 "2026-09-14T22:01:06Z")
One from Tolkien: There’s a Dwarven festival on a certain day of the year. If, on that day of the year, the Sun and Moon can be seen together in the sky, it’s called Durin’s Day, but (as of the time of the story) nobody any more has enough lore to predict whether that’ll happen in any given year. But it takes a remarkably small amount of astronomy lore to know that, on almost every day, there will be some time when both the Sun and Moon are up. ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [September 14, 2026, 10:41pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/182 "2026-09-14T22:41:19Z")
> [@Chronos](#): > > There’s a Dwarven festival on a certain day of the year. If, on that day of the year, the Sun and Moon can be seen together in the sky, it’s called Durin’s Day, but (as of the time of the story) nobody any more has enough lore to predict whether that’ll happen in any given year. > > But it takes a remarkably small amount of astronomy lore to know that, on almost every day, there will be some time when both the Sun and Moon are up. Not quite what he was driving at, I think. Tolkien was definitely quite astronomy-conscious and took things like lunar phases seriously in his worldbuilding! Thorin identifies “the first day of the dwarves’ New Year” as “the first day of the last moon of Autumn on the threshold of Winter”. The “first day of the last moon” phrasing suggests a definite characteristic lunar phase that marks the transition from one (synodic) month to the next. “Durin’s Day” refers specifically to when “the last moon of Autumn and the sun are in the sky together”. And indeed, on the Lonely Mountain in “the last week of autumn”, Bilbo happens to see “the orange ball of the sun sinking” in the west, and “there pale and faint was a thin new moon above the rim of Earth”. Evidently the “first day” of the month according to the dwarves occurs after new moon. But what’s at issue here is a problem in **determining the first visibility of the lunar crescent** , which [throughout the history of ancient astronomy was notoriously hard to predict](https://webspace.science.uu.nl/~gent0113/islam/islam_lunvis.htm). It’s still [a challenging problem for globally accurate predictions of month transitions in the Islamic calendar, which likewise begins months at first-crescent visibility](https://www.researchgate.net/publication/329308491_Analysis_of_Observations_of_Earliest_visibility_of_the_lunar_crescent). Whether observers will actually **see** the new crescent moon before sunset at the theoretically earliest possible moment depends on a lot of factors, including the moon’s position in its orbit, the sun’s longitude, the terrestrial latitude, and of course horizon terrain and weather. If “Durin’s Day” means that the very earliest appearance of the crescent moon is physically visible while the sun is still above the horizon, that’s not a trivial theoretical prediction, and it’s not surprising or anomalous that the dwarves of this period didn’t know how to do it. ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [September 14, 2026, 10:55pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/183 "2026-09-14T22:55:42Z")
P.S. This appears to be another instance of [Tolkien borrowing themes and tropes for Middle-earth Dwarves not only from Norse legends but also from Jewish history and culture.](https://en.wikipedia.org/wiki/Dwarves_in_Middle-earth#Jewish_history) Ancient Jewish observance of Rosh Hodesh or the first day of the new month likewise depended on physical observation of the first visible lunar crescent in the west (which generally happened **after** sunset). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 14, 2026, 10:57pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/184 "2026-09-14T22:57:20Z")
That just makes it worse, though. If the first day of the New Year is defined by the first visible crescent, then the Sun and Moon will absolutely be right next to each other in the sky. ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [September 14, 2026, 11:04pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/185 "2026-09-14T23:04:08Z")
But it’s very unlikely that you will **see** both sun and crescent moon at the theoretically earliest possible moment, while the sun is still above the horizon. The sun’s a fairly bright object, remember, and it tends to be hard to see stuff near it in the sky till after it sets! However, if that particular combination of date and place happens to give you an ecliptic/lunar orbit angle with an unusually large elongation of the new crescent away from the sun’s disk, then you may be able to see both of them together. Seriously, it’s a nontrivial spherical geometry and/or period-relations problem, ancient astronomers spent a lot of time coming up with prediction models for this sort of thing. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [September 14, 2026, 11:04pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/186 "2026-09-14T23:04:54Z")
> [@Kimstu](#): > > ISTM that the singer is telling his woman about **multiple** things he loves her for: only she “can see the changes” he’s been through, she “believed in” him, she’s “as constant as the northern star”, she’s “the brightest light [**not “star”**] that shines”. I don’t think that needs to be interpreted as claiming that the North Star itself actually **is** literally the brightest star in the sky; the singer just switched the figure of speech partway through the line. Hmm, good point. I actually like that song, and the lyrics are- _"You’ve been as constant as the Northern Star_ _The brightest light that shines, It’s been you, woman"_ ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [September 14, 2026, 11:24pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/187 "2026-09-14T23:24:33Z")
Are we talking about Middle Earth, where the moon is a flower and the sun is a fruit, and they both orbit the earth, which was once flat until it was bent into a sphere? I’m not sure normal astronomy rules apply. ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [September 14, 2026, 11:38pm UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/188 "2026-09-14T23:38:28Z")
Calendrically speaking, normal terrestrial astronomy rules definitely do seem to apply in Middle-earth, although Elves seem able to supersede them at times (cf. Eärendil). E.g., [Sam figuring out that the hobbits spent an unexpectedly long time in Lorien by reckoning up the shift in lunar phases](https://esl-bits.eu/ESL.English.Learning.Audiobooks/1%20LOTR/21/text.html): > [@](#): > > Sam sat tapping the hilt of his sword as if he were counting on his fingers, and looking up at the sky. ‘It’s very strange,’ he murmured. 'The Moon’s the same in the Shire and in Wilderland, or it ought to be. But either it’s out of its running, or I’m all wrong in my reckoning. You’ll remember, Mr. Frodo, the Moon was waning as we lay on the flet up in that tree: a week from the full, I reckon. And we’d been a week on the way last night, when up pops a New Moon as thin as a nail-paring, as if we had never stayed no time in the Elvish country. > > ‘Well, I can remember three nights there for certain, and I seem to remember several more, but I would take my oath it was never a whole month. Anyone would think that time did not count in there!’ […] > > ‘[…] But so it is, Sam: in that land you lost your count. There time flowed swiftly by us, as for the Elves. The old moon passed, and a new moon waxed and waned in the world outside, while we tarried there. And yestereve a new moon came again. […]’ ---
**Author:** ![Xocomil](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xocomil/32/14927_2.png) [@Xocomil](https://boards.straightdope.com/u/Xocomil)\ **Post date:** [September 15, 2026, 4:12am UTC](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849/189 "2026-09-15T04:12:09Z")
Just the idea of a crescent moon rising after the sun sets is making my head hurt. Like you said, a crescent moon rises shortly before sunrise or sets shortly after sunset. That reminds me of when a movie shows a sunset by playing a sunrise in reverse or vice versa. In the Northern Hemisphere, the sun rises and sets moving to the right. It it’s moving left, you’re in the Southern Hemisphere. [Previous page](https://boards.straightdope.com/t/glaring-astronomy-mistakes-in-a-movie-or-video/1032849.md?page=9)