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On Lunar Peregrinations

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On Lunar Peregrinations
Post by wingfield   » Fri Apr 19, 2019 7:20 am

wingfield
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Posts: 108
Joined: Sat Apr 25, 2015 11:15 pm
Location: Melbourne, Australia

Sitting observing the Easter full moon, I was reminded of something that hit me in the process of perpetual re-reading. Something about the moon was very wrong.

Now authors are not meant to be experts on everything but sometimes bits of text jar horribly, especially to someone who has dabbled in astronomy over several decades. We know that Safehold’s moon is slightly different from that of Earth but some things remain essentially the same, particularly in terms of orbital period or the approximate plane of the orbit in relation to that of Safehold around its star.

This is not the first time I have seen something wrong. Even Tolkien got it wrong on at least one occasion in The Lord of the Rings. Here is what I noticed, on page 169 of LAMA, hardback edition:

His gunners were sufficiently well trained to assuage any worries he might have felt on that score, and the moon would be rising within the hour. Not that it would be much help; they were just past the new moon, and the waxing crescent was little more than a nail paring.

The problem is that any moon that rises during the night is waning and is past the full. A brand new moon with a very thin crescent is already in the sky at sunset and sets soon afterward. As the moon waxes, the setting time gets later in the night until at full moon, it rises roughly at sunset and sets roughly at sunrise. Then, the waning moon rises later every night until a very old moon, once again being a very thin crescent, is rising not long before the sun. At new moon, the invisible moon is relatively close to the sun and travels through the sky in close company.

I hope that this will be of assistance for future reference for any author and anyone reading text that mentions the placement of the moon!
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Re: On Lunar Peregrinations
Post by Louis R   » Fri Apr 19, 2019 10:20 pm

Louis R
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Posts: 1143
Joined: Thu Jan 01, 2015 8:25 pm

Actually, this indicates that the moon in question is in a retrograde orbit.

At least that's what I have assumed every time I've read that passage

wingfield wrote:Sitting observing the Easter full moon, I was reminded of something that hit me in the process of perpetual re-reading. Something about the moon was very wrong.

Now authors are not meant to be experts on everything but sometimes bits of text jar horribly, especially to someone who has dabbled in astronomy over several decades. We know that Safehold’s moon is slightly different from that of Earth but some things remain essentially the same, particularly in terms of orbital period or the approximate plane of the orbit in relation to that of Safehold around its star.

This is not the first time I have seen something wrong. Even Tolkien got it wrong on at least one occasion in The Lord of the Rings. Here is what I noticed, on page 169 of LAMA, hardback edition:

His gunners were sufficiently well trained to assuage any worries he might have felt on that score, and the moon would be rising within the hour. Not that it would be much help; they were just past the new moon, and the waxing crescent was little more than a nail paring.

The problem is that any moon that rises during the night is waning and is past the full. A brand new moon with a very thin crescent is already in the sky at sunset and sets soon afterward. As the moon waxes, the setting time gets later in the night until at full moon, it rises roughly at sunset and sets roughly at sunrise. Then, the waning moon rises later every night until a very old moon, once again being a very thin crescent, is rising not long before the sun. At new moon, the invisible moon is relatively close to the sun and travels through the sky in close company.

I hope that this will be of assistance for future reference for any author and anyone reading text that mentions the placement of the moon!
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Re: On Lunar Peregrinations
Post by Isilith   » Fri Apr 19, 2019 11:32 pm

Isilith
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Louis R wrote:Actually, this indicates that the moon in question is in a retrograde orbit.

At least that's what I have assumed every time I've read that passage



That could be, but I would say that is unlikely. Such orbits are inherently unstable.
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Re: On Lunar Peregrinations
Post by Robert_A_Woodward   » Sat Apr 20, 2019 12:14 am

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Posts: 223
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Isilith wrote:
Louis R wrote:Actually, this indicates that the moon in question is in a retrograde orbit.

At least that's what I have assumed every time I've read that passage



That could be, but I would say that is unlikely. Such orbits are inherently unstable.


Triton is in an retrograde orbit around Neptune and astronomers believe that it is slowly decaying (it will take over a billion years to reach the Roche limit).
----------------------------
Beowulf was bad.
(first sentence of Chapter VI of _Space Viking_ by H. Beam Piper)
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Re: On Lunar Peregrinations
Post by Undercover Fat Kid   » Sun Apr 21, 2019 6:07 am

Undercover Fat Kid
Commander

Posts: 197
Joined: Sat Oct 12, 2013 10:20 pm

I want to take a moment to say that this is literally why I have never tried my hand at writing 8-)
.
.
Death is as a feather,
Duty is as a mountain
This life is a dream
From which we all
Must wake
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Re: On Lunar Peregrinations
Post by wingfield   » Sun Apr 21, 2019 9:00 am

wingfield
Lieutenant Commander

Posts: 108
Joined: Sat Apr 25, 2015 11:15 pm
Location: Melbourne, Australia

Isilith wrote:
Louis R wrote:Actually, this indicates that the moon in question is in a retrograde orbit.

At least that's what I have assumed every time I've read that passage



That could be, but I would say that is unlikely. Such orbits are inherently unstable.

Retrograde orbits are much more plausible when something like a gas giant captures another satellite.

To return to the subject of my discussion, expecting moonrise for a brand new moon in a retrograde orbit would mean waiting until very late in the night (not long before the dawn - the sky would be growing light). The entire action that followed that night took place in full dark, with the little surprise of the illumination ordered by Hanth as the Desnairians charged.

RFC does not appear to have mentioned that the moon is in a retrograde orbit.
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Re: On Lunar Peregrinations
Post by Andriarivera   » Fri May 10, 2019 7:13 am

Andriarivera
Midshipman

Posts: 1
Joined: Fri May 10, 2019 7:07 am

I agree with wingfield, Moon is not available in the orbit.
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Re: On Lunar Peregrinations
Post by jgnfld   » Sun May 12, 2019 9:56 pm

jgnfld
Captain of the List

Posts: 454
Joined: Sat Dec 28, 2013 8:55 am

Andriarivera wrote:I agree with wingfield, Moon is not available in the orbit.



A few years back, one dreadful boy ran up to me and said, “Mr. Bradbury?”

“Yes?” I said.

“That book of yours, The Martian Chronicles?” he said.

“Yes,” I said.

“On page 92 where you have the moons of Mars rising in the east?”

“Yeah,” I said.

“Nah,” he said.

So I hit him. [attributed to Ray Bradbury himself]

:)
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Re: On Lunar Peregrinations
Post by richardinor   » Sat Jun 01, 2019 12:58 am

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Commander

Posts: 199
Joined: Sat Jul 31, 2010 12:23 am
Location: Oregon

Not something I would have noticed. I noticed no RFC comments.
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