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Old Jun 1 2015, 12:25 AM   #1
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Default The Size of Pern

Sorry if there's already a thread for this- or several- but I searched and couldn't find them. Anyway, ever since I started my Minecraft project, I've been wondering, how big is Pern? Could it actually exist as a real planet? And could it hold on to those two moons? Pern's bigger moon is about the size of Earth's Luna, with the smaller moon being just under that size.

Also makes me wonder if Pern ever got both its moons in eclipse at the same time... I bet that would've been cool to see.

Looking through DLG since I seem to have misplaced my copy of DragonsDawn/Chronicles of Pern, it says that Pern has a diameter of "approximately" 6500 miles. So that puts it at about a 1000 miles smaller than Venus, but still bigger than Mars by at least 2000 miles. (Thank you Google!) "The diameter of Venus is 12,092 km (only 650 km less than Earth's) and its mass is 81.5% of Earth's." (http://en.wikipedia.org/wiki/Venus)

The Northern Continent of Pern is said to be about the same size as Earth's Eurasian landmass (21.14 million sq miles (54.76 million km²)), with the Southern Continent taking up over half of the landmass of the whole planet, and the Western Continent and all those smaller islands taking up the leftover landmass. The ocean is said to be 5000 miles wide (in between the sizes of Earth's Atlantic and Pacific), and Pern has about the same gravity as Earth (according to Pernwiki: "Gravity was 0.9 (probably meaning that it was 90% of earth's gravity)")...

So how dense would that make Pern? Has anybody measured the Northern Continent in the Atlas to see if it matches up?

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Old Jun 2 2015, 04:56 AM   #2
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Default Re: The Size of Pern

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Originally Posted by CuriousFlit View Post
Sorry if there's already a thread for this- or several- but I searched and couldn't find them. Anyway, ever since I started my Minecraft project, I've been wondering, how big is Pern? Could it actually exist as a real planet? And could it hold on to those two moons? Pern's bigger moon is about the size of Earth's Luna, with the smaller moon being just under that size.

Also makes me wonder if Pern ever got both its moons in eclipse at the same time... I bet that would've been cool to see.

Looking through DLG since I seem to have misplaced my copy of DragonsDawn/Chronicles of Pern, it says that Pern has a diameter of "approximately" 6500 miles. So that puts it at about a 1000 miles smaller than Venus, but still bigger than Mars by at least 2000 miles. (Thank you Google!) "The diameter of Venus is 12,092 km (only 650 km less than Earth's) and its mass is 81.5% of Earth's." (http://en.wikipedia.org/wiki/Venus)

The Northern Continent of Pern is said to be about the same size as Earth's Eurasian landmass (21.14 million sq miles (54.76 million km²)), with the Southern Continent taking up over half of the landmass of the whole planet, and the Western Continent and all those smaller islands taking up the leftover landmass. The ocean is said to be 5000 miles wide (in between the sizes of Earth's Atlantic and Pacific), and Pern has about the same gravity as Earth (according to Pernwiki: "Gravity was 0.9 (probably meaning that it was 90% of earth's gravity)")...

So how dense would that make Pern? Has anybody measured the Northern Continent in the Atlas to see if it matches up?
Acceleration due to gravity is: g = G M / r^2

Putting the numbers in - g=0.9*9.81, G=6.67e-11, r=5.2e6 - gives a mass of 3.6e24 kg or 60% of the Earth's mass. In terms of density, Pern has a density of 60%*(6.3/5.2)^3=107% of Earth's average density.

Timor having a size comparable to our own moon is, if you'll excuse the pun, improbable lunacy! Planet formation doesn't lend itself to massive moons, but if we do let Anne get away with it, then Pern must have had some major planetary trauma in the past. That could also explain its higher density - much like Mercury, it could have a larger than expected iron core and a smaller mantle following a moon-making collision.

No comment on eclipses, except that they're very unlikely to be total.
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Old Jun 2 2015, 05:30 AM   #3
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Default Re: The Size of Pern

Kath: I thought for a moment that you had started your 2nd equation with "-g".
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Old Jun 2 2015, 06:06 PM   #4
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Default Re: The Size of Pern

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Acceleration due to gravity is: g = G M / r^2

Putting the numbers in - g=0.9*9.81, G=6.67e-11, r=5.2e6 - gives a mass of 3.6e24 kg or 60% of the Earth's mass. In terms of density, Pern has a density of 60%*(6.3/5.2)^3=107% of Earth's average density.

Timor having a size comparable to our own moon is, if you'll excuse the pun, improbable lunacy! Planet formation doesn't lend itself to massive moons, but if we do let Anne get away with it, then Pern must have had some major planetary trauma in the past. That could also explain its higher density - much like Mercury, it could have a larger than expected iron core and a smaller mantle following a moon-making collision.
That sounds plausible enough when explained that way. Scientists have found weirder things out in space so far.

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No comment on eclipses, except that they're very unlikely to be total.
What makes you say that? Would having two moons make that much of a difference?
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Old Jun 3 2015, 04:45 AM   #5
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What makes you say that? Would having two moons make that much of a difference?
Timor is roughly the size of Luna, but not at the same distance. We don't know the angular size of 'Rukbat' in the sky (ask me in a couple of months when I'm less busy and I'll let you know just how impossible Pern's orbit is around a star of that spectral type and mass...) but neither moon is likely to be exactly the same size as that of Pern's sun, or even close to it. They'll also be different sizes themselves (I think we know that Belior is close enough that it *appears* bigger than Timor... again, if anyone cares, I can chuck some numbers at that question later in the summer), and while they may be resonantly locked to each other, you also have to factor in the latitude of the observer and the tilt to the plane of their orbits. Eclipses are unlikely for one moon, and adding a second really doesn't help all that much.

The fact that we have eclipses is a deeply freaky coincidence of size, placement and timing (come back in X million years and the moon will have moved too far out to give us total eclipses).
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Old Jun 4 2015, 08:15 PM   #6
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Just like the 'bad bad blow' report by the dolphins in The Dolphins of Pern it came at the equinox or the storm that Robinton and Kasia were caught in, she sailed them out the eye into a safe place. The Masterharper of Pern
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Old Jun 5 2015, 02:42 AM   #7
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Default Re: The Size of Pern

You'd think that a so-called intelligent man like Robinton would learn. First; Kasia has to save him from one storm. Sometime later; Menolly has to save him from another!
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Old Jun 5 2015, 07:37 AM   #8
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Default Re: The Size of Pern

Quote:
Originally Posted by CuriousFlit View Post
Sorry if there's already a thread for this- or several- but I searched and couldn't find them. Anyway, ever since I started my Minecraft project, I've been wondering, how big is Pern? Could it actually exist as a real planet? And could it hold on to those two moons? Pern's bigger moon is about the size of Earth's Luna, with the smaller moon being just under that size.

Also makes me wonder if Pern ever got both its moons in eclipse at the same time... I bet that would've been cool to see.

Looking through DLG since I seem to have misplaced my copy of DragonsDawn/Chronicles of Pern, it says that Pern has a diameter of "approximately" 6500 miles. So that puts it at about a 1000 miles smaller than Venus, but still bigger than Mars by at least 2000 miles. (Thank you Google!) "The diameter of Venus is 12,092 km (only 650 km less than Earth's) and its mass is 81.5% of Earth's." (http://en.wikipedia.org/wiki/Venus)

The Northern Continent of Pern is said to be about the same size as Earth's Eurasian landmass (21.14 million sq miles (54.76 million km²)), with the Southern Continent taking up over half of the landmass of the whole planet, and the Western Continent and all those smaller islands taking up the leftover landmass. The ocean is said to be 5000 miles wide (in between the sizes of Earth's Atlantic and Pacific), and Pern has about the same gravity as Earth (according to Pernwiki: "Gravity was 0.9 (probably meaning that it was 90% of earth's gravity)")...

So how dense would that make Pern? Has anybody measured the Northern Continent in the Atlas to see if it matches up?
The current theory on how the earth got its moon,http://en.wikipedia.org/wiki/Giant_impact_hypothesis is that early in the earths formation an object the size of mars struck the earth at a glancing angle. This put material into orbit above the Roche radius then the moon coalesced. It is possible that this happened twice or that the impact was so strong that it sent up two different streams that coalesced in two different places. This would also explain why Pern is dense if it had two impacts. Although I can not imagine how Pern still has a 24hour day with two moons dragging on it.
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Old Jun 5 2015, 07:51 AM   #9
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Pern's northern continent can not be as large as Eurasia. Think about how long it would take on foot to go from Lisbon to Seoul. That would be the same as walking from Tillek to Benden Wyer. Also I can't imagine that with all that space how only 6million people are crowded.
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Old Jun 5 2015, 12:26 PM   #10
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The current theory on how the earth got its moon,http://en.wikipedia.org/wiki/Giant_impact_hypothesis is that early in the earths formation an object the size of mars struck the earth at a glancing angle. This put material into orbit above the Roche radius then the moon coalesced. It is possible that this happened twice or that the impact was so strong that it sent up two different streams that coalesced in two different places. This would also explain why Pern is dense if it had two impacts. Although I can not imagine how Pern still has a 24hour day with two moons dragging on it.
If I remember right, Pern has a 26 hour day. Will have to look that up again though...
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Old Jun 5 2015, 12:29 PM   #11
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Pern's northern continent can not be as large as Eurasia. Think about how long it would take on foot to go from Lisbon to Seoul. That would be the same as walking from Tillek to Benden Wyer. Also I can't imagine that with all that space how only 6million people are crowded.
Considering that they can't spread out too much because of Thread and lack of growing areas for crops due to all the mountains, I think I could see what they meant.
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Old Jun 8 2015, 03:59 PM   #12
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P'ter - was the storm with Menolly also at the Equinox? If not, then the foolishness was in ever going to sea again!
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Old Jun 11 2015, 12:14 PM   #13
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Pern's northern continent can not be as large as Eurasia. Think about how long it would take on foot to go from Lisbon to Seoul. That would be the same as walking from Tillek to Benden Wyer.
Could it be as large if you counted all of the snowy wastes as well as the habitable land? Do we really know how big the wastes are?
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Old Jul 26 2015, 08:06 PM   #14
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Pern's northern continent can not be as large as Eurasia. Think about how long it would take on foot to go from Lisbon to Seoul. That would be the same as walking from Tillek to Benden Wyer. Also I can't imagine that with all that space how only 6million people are crowded.
It could quite easily be that large. Canada has a large expanse of space, but the population is concentrated along the southern edge and some areas are crowded.
With limited agricultural space and the difficulty of spreading out in the face of Threadfalls, the population will concentrate. During Intervals, it would require a concerted effort to establish a new minor hold on the edge of lands held by a major hold.

This does not, however, rule out small independent holds being scattered across the continent between the major holds. These would serve as way stations/havens for trader caravans traversing the continent. Much of the travelling would be done by sea as it would be faster.
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Old Feb 21 2016, 04:46 PM   #15
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I looked at the atlas of Pern and discovered something interesting. The size of the northern continent is only 1000 miles from Tillek to Benden and only 3 northern continents fit on the globe, or about 3000miles.This means that the size of the northern continent is the distance from New York to Chicago and that Pern is only the size of the Earths moon.
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Old Feb 21 2016, 06:31 PM   #16
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That IS interesting. O_o I have the atlas too and I never noticed that. The author who made the Pern atlas says in the book that she measured the distances by charting out Pern "time zones" and based on how long travel time was and compared that to how long travel of the same kind here on Earth would take, if I'm reading this right. She got 9 time zones across the Northern Continent, and 14 across what we've seen so far of the Southern.

But brings us right back to square one. Just how big or small IS Pern?
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Old Feb 25 2016, 04:12 AM   #17
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My headcanon's always been "Earth-sized, give or take." There are a lot of wonderful things about the Pern series, but Anne McCaffrey's math skills aren't one of them. These are the same books that give us the meter/foot dragons, and a colony going from 6,000 people to 20,000 people in 8 years.

I think it's more important to take the gist of what the story was supposed to convey and not get hung up on the hard numbers, because the numbers don't make much sense.
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Old Feb 25 2016, 05:21 AM   #18
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Default Re: The Size of Pern

I've always gone with "Parallels Earth" myself and assumed that it must be about the same, give or take a little.

As for the 2 moons ... is it possible Belior is particularly small? Or would that have eventually resulted in it crashing into Pern/Timor due to gravity stuff?
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Old Feb 25 2016, 04:04 PM   #19
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I've always been of the opinion that Pern is perhaps smaller than Earth. Perhaps half up to three quarters the size of Terra with a slower rotation to take into account the longer day.

I don't think it's ever been made clear on the size and orbital position of the two Moons, but I could be wrong.
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