# "It was a dark evening with only the feeble light of a waning crescent moon." How much basic astronomy is widely understood by those not specifically interested in the subject?
**URL:** https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200
**Category:** In My Humble Opinion
**Created:** [November 2, 2022, 8:29am UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200 "2022-11-02T08:29:28Z")
**Posts on this page:** 20
**Page:** 7
### Author:  [@K364](https://boards.straightdope.com/u/K364)
#### Post date: [November 5, 2022, 4:18pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/121 "2022-11-05T16:18:19Z")
Yes, the moon doesn’t “point” exactly at the sun. It’s an illusion and you will find explanations and it sounds like you have one.
I think it has to do with our perception of the bowl that we see as the sky. We see the moon and the sun as two objects on the same bowl - the same distance. But the sun is actually 400 times further away. If you draw the two triangles (earth-moon-sun), one with equilateral sides, and one with the true sides you can see the geometry of the illusion.
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [November 5, 2022, 4:21pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/122 "2022-11-05T16:21:44Z")
Now I’m wondering if there are novels with deliberate mistakes just for fun. Something like “although it was raining heavily, the light of the full moon helped him see”. 😛
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [November 5, 2022, 4:27pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/123 "2022-11-05T16:27:09Z")
> [@DesertDog](#):
>
> > [@TheTooth](#):
> >
> > On a related note, a friend of mine has made it almost to retirement age without knowing the order of the colors on the spectrum. That surprised me
>
> Especially since his name was Roy G. Biv.
I’ve always been pretty sceptical of “indigo”. If there’s a band between blue and violet on the spectrum it’s pretty darn narrow. I suspect someone decided it just had to be seven colors for some reason.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [November 5, 2022, 4:36pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/124 "2022-11-05T16:36:42Z")
> [@K364](#):
>
> Yes, the moon doesn’t “point” exactly at the sun. It’s an illusion and you will find explanations and it sounds like you have one.
No, it does point exactly at the Sun. It’s not an illusion at all. What’s going on with @eburacum45 's picture is that “exactly at the Sun” isn’t the direction one might think it is.
> [@Lumpy](#):
>
> I suspect someone decided it just had to be seven colors for some reason.
Yup, Newton, for mostly-mystical reasons, but also by analogy with the seven notes of the scale.
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### Author:  [@eburacum45](https://boards.straightdope.com/u/eburacum45)
#### Post date: [November 5, 2022, 5:06pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/125 "2022-11-05T17:06:46Z")
> [@Chronos](#):
>
> No, it does point exactly at the Sun. It’s not an illusion at all. What’s going on with @eburacum45 's picture is that “exactly at the Sun” isn’t the direction one might think it is.
That’s right. I try to visualise this as the Moon and the Sun as lying on a great circle in the sky, that divides the sky exactly in half. If you could orient yourself so that you were perpendicular to that circle, you could see that the Moon is pointing directly at the Sun. But this circle is tilted with respect to the horizon, so that the Moon looks like it is pointing ‘upwards’ and the Sun is invisible below the horizon.
Indeed, the centre of the illuminated portion of the Moon and the Sun are joined by an invisible chord that also crosses the sky at a weird angle, but with enough mental gymnastics you can visualise it. This almost scared me the first time I saw it - it looks like a glitch in the Matrix.
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### Author:  [@Max\_S](https://boards.straightdope.com/u/Max_S)
#### Post date: [November 5, 2022, 5:16pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/126 "2022-11-05T17:16:37Z")
> [@Spectre\_of\_Pithecanthropus](#):
>
> I forget in which book it was in, but there is a passage where the characters have to go outside just after dark, and it’s mentioned that there’s a waning crescent moon. This is impossible, because a waning crescent won’t rise until the night’s nearly over.
> [@gnarator](#):
>
> by waning crescent, it’s 3 or 4 in the morning before it rises.
Unless I’m mistaken, that’s not necessarily true if you live far enough from the equator (i.e. North, as you’d have to be in Antarctica if you are going South). For example in say, Reykjavik (capital of Iceland), for a few days in late July the waning crescent moon will be up 24 hours a day while the Sun sets at say 10 or 11 pm.
~Max
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### Author:  [@DesertDog](https://boards.straightdope.com/u/DesertDog)
#### Post date: [November 5, 2022, 6:54pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/127 "2022-11-05T18:54:02Z")
> [@Chronos](#):
>
> Yup, Newton, for mostly-mystical reasons, but also by analogy with the seven notes of the scale.
And a lot of other mystical sevens, including the planets – including the moon as a planet but excluding anything past Saturn, having not been discovered yet.
For the record, I’ve not been able to distinguish indigo in sun spectra.
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### Author:  [@DPRK](https://boards.straightdope.com/u/DPRK)
#### Post date: [November 5, 2022, 7:12pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/128 "2022-11-05T19:12:37Z")
Look at e.g. the flag of Algeria and you will approach some absurdities:
> **[File:Flag of Algeria.svg](https://en.wikipedia.org/wiki/File:Flag_of_Algeria.svg)**
>
> Original file (SVG file, nominally 900 × 600 pixels, file size: 311 bytes)
> In order to be hosted on Commons, all works must be in the public domain in the United States as well as in their source country. The copyright of all Algerian photographs and works of applied art published prior to 1948 had expired in Algeria on the date of restoration (April 19, 1998) pursuant to the provisions of Article 60 of the defunct Ordinance No. 97-10 of 6 March 1997 which was in effect at the time. Such works ...
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### Author:  [@mordecaiB](https://boards.straightdope.com/u/mordecaiB)
#### Post date: [November 5, 2022, 8:14pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/129 "2022-11-05T20:14:46Z")
> [@Jas09](#):
>
> The Sherlock Holmes quote about not knowing that the earth revolves around the sun is appropriate here:
>
> > [@](#):
> >
> > “What the deuce is it to me?” he interrupted impatiently; "you say that we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or to my work.”
I like this one [better](https://www.sunnyskyz.com/funny-jokes/20/Sherlock-Holmes-and-Dr-Watson-Go-Camping).
> Sherlock Holmes and Dr. Watson decide to go on a camping trip. After dinner and a bottle of wine, they lay down for the night, and go to sleep.
>
> Some hours later, Holmes awoke and nudged his faithful friend.
>
> “Watson, look up at the sky and tell me what you see.”
>
> Watson replied, “I see millions of stars.”
>
> “What does that tell you?”
>
> Watson pondered for a minute.
>
> “Astronomically, it tells me that there are millions of galaxies and potentially billions of planets.”
> “Astrologically, I observe that Saturn is in Leo.”
> “Horologically, I deduce that the time is approximately a quarter past three.”
> “Theologically, I can see that God is all powerful and that we are small and insignificant.”
> “Meteorologically, I suspect that we will have a beautiful day tomorrow.”
> “What does it tell you, Holmes?”
>
> Holmes was silent for a minute, then spoke: “Watson, you idiot. Someone has stolen our tent!”
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### Author:  [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)
#### Post date: [November 5, 2022, 8:20pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/130 "2022-11-05T20:20:20Z")
Agreed. I’d be very surprised if 1% of the population knew that and wouldn’t be shocked if it was much much less well known.
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### Author:  [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)
#### Post date: [November 5, 2022, 8:39pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/131 "2022-11-05T20:39:50Z")
Until I got glasses at age 10, I thought the moon was just a blurry light in the sky. It seemed to get brighter and dimmer, but I certainly couldn’t make out phases.
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### Author:  [@DPRK](https://boards.straightdope.com/u/DPRK)
#### Post date: [November 5, 2022, 11:16pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/132 "2022-11-05T23:16:09Z")
> [@commasense](#):
>
> the moon rises some time after sunset, but then sets before sunrise. I started wondering about this the last time I read the book, a few years ago, and although I’m still 90% sure it’s impossible, I was wondering whether there might not be some times of year and some places, perhaps in higher lattitudes, where it could happen.
I don’t think it is too hard to arrange. As a first attempt, flipping through the almanac, take a point on the Prime Meridian 62 degrees north, and go to June 14, 2022. Looks like the sun sets at 21:50, the moon barely rises around 23:19 and then sets around 1:45 before the sun rises at 2:11.
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### Author:  [@Max\_S](https://boards.straightdope.com/u/Max_S)
#### Post date: [November 6, 2022, 3:04am UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/133 "2022-11-06T03:04:25Z")
> [@DPRK](#):
>
> Look at e.g. the flag of Algeria and you will approach some absurdities
I assumed they were Toy Story fans.
~Max
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### Author:  [@commasense](https://boards.straightdope.com/u/commasense)
#### Post date: [November 6, 2022, 5:32am UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/134 "2022-11-06T05:32:23Z")
Okay, so it can and does happen in some parts of the world. My second thoughts were justified. Thanks.
But I don’t think TWITW was supposed to be set in the middle of the Norwegian Sea between the Faroe Islands and the coast of Norway. A quick look at a few tables for Berwick Upon Tweed, one of the northernmost towns in England, suggests that it may not happen that far south, although my search was far from exhaustive.
I suspect this was an error on Grahame’s part, based on the naive idea that the sun is up in the day and the moon is up at night, so the moon must rise and set while the sun is down. But as I said, the whole episode is fantasy, so we shouldn’t cavil at scientific inaccuracies.
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### Author:  [@wolfpup](https://boards.straightdope.com/u/wolfpup)
#### Post date: [November 6, 2022, 8:27am UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/135 "2022-11-06T08:27:01Z")
> [@pulykamell](#):
>
> Also between the tropics too, right? At certain times of year, the midday sun may be to the north of you in the northern hemisphere, for instance.
Right. At the equator, the midday sun is directly overhead only at the spring and fall equinox. In the NH summer, the equatorial sun is always in the northern half of the sky, and in the SH summer, it switches to the southern half. The northern and southern tropic lines are the furthest from the equator you can get and still get the midday sun directly overhead, which only happens at the summer solstice in the respective hemisphere.
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### Author:  [@Bootb](https://boards.straightdope.com/u/Bootb)
#### Post date: [November 6, 2022, 2:56pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/136 "2022-11-06T14:56:44Z")
> [@Lumpy](#):
>
> Now I’m wondering if there are novels with deliberate mistakes just for fun. Something like “although it was raining heavily, the light of the full moon helped him see”. 😛
What makes you think that that would be a mistake? I’ve seen rainfall while the sun was shining.
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### Author:  [@K364](https://boards.straightdope.com/u/K364)
#### Post date: [November 6, 2022, 3:28pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/137 "2022-11-06T15:28:35Z")
> [@Chronos](#):
>
> No, it does point exactly at the Sun. It’s not an illusion at all. What’s going on with @eburacum45 's picture is that “exactly at the Sun” isn’t the direction one might think it is.
Yes, I mangled my wording. I meant that we expect to see different geometry than what we are actually seeing.
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### Author:  [@Odesio](https://boards.straightdope.com/u/Odesio)
#### Post date: [November 6, 2022, 3:40pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/138 "2022-11-06T15:40:53Z")
> [@Spectre\_of\_Pithecanthropus](#):
>
> What I want to ask is this: How much general knowledge of astronomy is it fair to assume people typically have? We can safely assume everyone knows the sun rises in the east and sets in the west, and why the days are long in the summer and short in the winter, and _why_ the moon has phases even if they don’t fully think that through to understand what time of the day or night you can see a given lunar phase.
I remember one of my anthropology professors asking us when the next full moon was and nobody knew. (He asked us about a few other questions about nature that most of us couldn’t answer.) His rhetorical question after all those was, “Why don’t you know this?” And the answer was “Because it’s not important to you.”
I would completely miss that crescent moon reference. I understand which direction the sun rises, have a basic understanding of seasons, phases of the moon, how the planets move, and that we’re in a heliocentric solar system, but that’s about it.
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### Author:  [@DPRK](https://boards.straightdope.com/u/DPRK)
#### Post date: [November 6, 2022, 5:05pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/139 "2022-11-06T17:05:21Z")
> [@commasense](#):
>
> But I don’t think TWITW was supposed to be set in the middle of the Norwegian Sea between the Faroe Islands and the coast of Norway. A quick look at a few tables for Berwick Upon Tweed, one of the northernmost towns in England, suggests that it may not happen that far south, although my search was far from exhaustive.
That was only our first attempt. For a second attempt, let’s consider the year 2025, just because the moon is more “extreme”. For Berwick-Upon-Tweed let’s take N 55°46′09″ W 02°00′09″
Consider the evening of 12 May. The sun sets at 19:52 (Universal Time). The moon rises at (you should probably check this!!!) 20:25, when it is starting to get dark. It rises through the Southern sky and sets… at 3:20. But the sun is not yet up! It rises at 3:44.
There should be a number of other examples…
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### Author:  [@commasense](https://boards.straightdope.com/u/commasense)
#### Post date: [November 6, 2022, 6:45pm UTC](https://boards.straightdope.com/t/it-was-a-dark-evening-with-only-the-feeble-light-of-a-waning-crescent-moon-how-much-basic-astronomy-is-widely-understood-by-those-not-specifically-interested-in-the-subject/974200/140 "2022-11-06T18:45:18Z")
Well done!
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