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Is this a realistic conastronomy?

Posted: Sun 26 Nov 2017, 22:20
by Illuminus
(The reason I'm not posting this in the Conworld section is because I'm a beginner and worried this is unrealistic, but if you want to move this, by all means go ahead.)

Kímera is 4% larger than Earth, although its density is almost equivalent. Its water-to-land ratio is about 55:45. The average temperature on Kímera is 70 degrees fahrenheit. The average temperature near the equator is 90 degrees; the poles, -70. It varies on location and season, however.
The sun is called Alda, with surface temperature at an average of 6,490 kelvin degrees. It is an F-type, main sequence star. Kímera is in the habitable zone of Alda, at nearly 100 million miles away from the sun.
Kímera has three moons called Tovanil, Andor, and Vîtus, in order from furthest to closest from Kímera. It is the only planet orbiting Alda.

[->] Vîtus has a radius of 811 miles and is 201,036 miles from Kímera, and takes 34 Earth days to orbit Kímera
[->] Andor has a radius of 856 miles and is 219,154 miles from Kímera, and takes 36 Earth days to orbit Kímera
[->] Tovanil has a radius of 990 miles and is 224,209 miles from Kímera, and takes 37 Earth days to orbit Kímera

It takes Kímera 386 Earth days to orbit Alda.

I'm mostly concerned about the moons. Are they too close to each other? Too far away? Is the year too long in regards to the planet and sun's size and distance from each other? Really just wondering if anything raises an eyebrow.

Re: Is this a realistic conastronomy?

Posted: Sun 26 Nov 2017, 23:03
by Pabappa
The year length has varied within the history of Earth itself, so a value just slightly different than ours is surely ok.

Temperatures are in Fahrenheit I assume? That seems reasonable, given the higher amount of land.... But for the *average* temperatures to be that far apart I think you'll need a large landmass at both poles.

Re: Is this a realistic conastronomy?

Posted: Sun 26 Nov 2017, 23:16
by Illuminus
Pabappa wrote:
Sun 26 Nov 2017, 23:03
you'll need a large landmass at both poles.
Yeah, fortunately I have made a map of the world yet--so will do! By large do you mean Antarctica sized or bigger, like Africa?
Pabappa wrote:
Sun 26 Nov 2017, 23:03
Temperatures are in Fahrenheit I assume?
Yep, that's probably worthy of noting somewhere.

Re: Is this a realistic conastronomy?

Posted: Mon 27 Nov 2017, 00:52
by sangi39
I tend to use "Creating an Earthlike Planet" by Geoff Eddy (which annoyingly can take a bit of tracking down online but IIRC it's been circling the internet here and there for years now despite the original page going down), but he suggests using Kepler's Third Law, (T^2)=(R^3) where T is the orbital period and R is the orbital distance, but in relation to Earth. For the units you've given, this would give your planet an orbital period of 407.517 (Earth) days (how long a day is on your planet will obviously change the number of Kímeran days the year lasts).

However, he also suggests that habitable planets orbiting F-type main sequence stars (although he only provides data for F0 and F5 main sequence stars) should orbit at between 1.51AU and 3.45AU depending on the mass (and thus the temperature) of the star, which give orbital periods of between 592 Earth days and 1793 Earth days. Kímera orbits at just 1.07Au which would be fine for a habitable planet orbiting a G-type main sequence star like our Sun but is a little too close for an F-type one (or so says Geoff).

The three moons are probably much too close to each other. IIRC, sufficiently large bodies that are close enough too each other will fall into some sort of orbital resonance (although I could be wrong), so ratios like 1:2:4 for the orbital periods would probably be more likely than what you have at the moment (IIRC, there's a suggestion that this might tie in with Bode's Law which suggests that each subsequent orbiting body is roughly twice as far away as the previous one from the thing they're orbiting).

So, for example, if Vîtus orbits at, say, 321,869km (200,000 miles), which would give it an orbital period of about 20.5 days (if I've done the maths right). If we then double that for each subsequent moon, Andor would orbit at 510,000km for 41 days and Tovanil would orbit at 809,000km for 82 days (ish, I've more or less fudged the numbers there and assumed each moon has the same mass given their similar radii). You could bring them closer, which would shorten their orbital periods (for example, if you bring Vîtus in so it's about 144,000km away, it would appear in the sky to be the same size as our Moon, but would orbit once every 6 days or so and Andor and Tovanil would only have orbital periods of 12 and 24 days).

Re: Is this a realistic conastronomy?

Posted: Mon 27 Nov 2017, 01:43
by Illuminus
Thank you for the thorough answer, that was very helpful. Could I reduce the temperature of Alda instead of changing Kímera's distance to it--if so, would 5,890 degrees fahrenheit be reasonable? I've edited the moons accordingly, thanks for that as well! [:D]

Re: Is this a realistic conastronomy?

Posted: Mon 27 Nov 2017, 02:12
by sangi39
Illuminus wrote:
Mon 27 Nov 2017, 01:43
Thank you for the thorough answer, that was very helpful. Could I reduce the temperature of Alda instead of changing Kímera's distance to it--if so, would 5,890 degrees fahrenheit be reasonable? I've edited the moons accordingly, thanks for that as well! [:D]
I think 5,890 would work. That would make it a heavy-ish G-type main sequence star with a mass about 1.019 times that of our Sun. With an orbital period of 407.517 (Earth) days that's well within the 385.59 to 666.75 Earth day guideline suggested by Geoff Eddy [:)]

Oh wait, Fahrenheit? No, that would make it a small red dwarf. 5,890F is only 3,500-ish Kelvin.

Most sites I've used will use metric units for mass and distance and then Kelvin for temperature rather the Celsius or Fahrenheit. You're using Kelvin and Fahrenheit in the same description.

Actually, on the note of temperature, I might have to agree with Pabappa, but only based on a cursory search, about the surface temperatures of Kímera. The North and South poles on Earth have average yearly temperatures of -18C and -52C respectively bringing the "average polar" temperature to -35C. The equatorial temperatures do tend to be around 30C which you have, but the average surface temperature on Earth is only about 15C, not the 24C you have. I'd assume, though, that you could chalk that up to where the landmasses are, albedo, greenhouse effect, cloud cover, etc. so all in all I'd say the temperatures overall probably do work at the moment, but they'd probably change once you start building the world itself or it would restrict what you can actually do (there's a YouTuber called Artifexian who coincidentally covered this exact topic earlier today).

Re: Is this a realistic conastronomy?

Posted: Mon 27 Nov 2017, 02:49
by Illuminus
sangi39 wrote:
Mon 27 Nov 2017, 02:12

Oh wait, Fahrenheit? No, that would make it a small red dwarf. 5,890F is only 3,500-ish Kelvin.
Ach, I meant to type Kelvin, sorry! [xD]
sangi39 wrote:
Mon 27 Nov 2017, 02:12

Actually, on the note of temperature, I might have to agree with Pabappa, but only based on a cursory search, about the surface temperatures of Kímera. The North and South poles on Earth have average yearly temperatures of -18C and -52C respectively bringing the "average polar" temperature to -35C. The equatorial temperatures do tend to be around 30C which you have, but the average surface temperature on Earth is only about 15C, not the 24C you have. I'd assume, though, that you could chalk that up to where the landmasses are, albedo, greenhouse effect, cloud cover, etc. so all in all I'd say the temperatures overall probably do work at the moment, but they'd probably change once you start building the world itself or it would restrict what you can actually do (there's a YouTuber called Artifexian who coincidentally covered this exact topic earlier today).
I'll adjust the temperatures a little along with those other features you mentioned, thanks!

Re: Is this a realistic conastronomy?

Posted: Wed 29 Nov 2017, 03:27
by Axiem
Keep in mind that the only way to answer "is this n-body system stable" is to actually run a simulation of the system and see what happens over millions of years.

For your various numbers and such, are you just coming up with them off the top of your head, or are you actually calculating them and making sure they're part of a coherent system?

Regarding year length, for instance, that's not just something you can say (also, note that "length of year" and "period around star" are two different things); it's very directly related to the masses of the two bodies and the distance between them. Rather, the period around the star is; the length of the year also requires knowing the rotational period of the planet.

I have a fair amount of spreadsheeting and simulation scripts for doing this (as I've Done the Math on my own conworld), I just need to stop being shy and post them.

Re: Is this a realistic conastronomy?

Posted: Thu 30 Nov 2017, 01:38
by Shemtov
I recommend watching Artefexian's videos on world building. He gets into the nitty-gritty of the math (which is why I say that my conworld is Earth, but with different continents- I'm terrible with math, though he has created spreadsheets that do the math for you and links to pre-existing sites that calculate stuff like this, when available). He also has good Intro vids for beginning conlangers.

Re: Is this a realistic conastronomy?

Posted: Thu 30 Nov 2017, 04:07
by Axiem
I don't know that Artifexian gets into the nitty-gritty of the math*; he does gloss over a decent amount. But I also love Artifexian, and it's a great introduction to how this is all linked together. It's a great place to start.


*: For instance, I don't know that he ever covers the effect the procession of a planet's axis has on year/day length. And somewhere amidst all of my math research, I ended up digging into an academic paper that worked out the projected latitudes of atmospheric cells based on rotation speed of the surface and a handful of other things; also, I tried to work through the math once upon a time to figure out the ellipticity of my planet based on its density and rotation speed. I maaaaaaay be a bit of an overachiever, though.

Re: Is this a realistic conastronomy?

Posted: Thu 30 Nov 2017, 04:43
by Ahzoh
Artifexian was how I learned about roche limits and the effects a ring would have a planet like Earth. You never really think of a ring having a huge shadow on a planet.

Re: Is this a realistic conastronomy?

Posted: Fri 01 Dec 2017, 02:16
by Illuminus
Regarding Axiem's comment:
Eh, I made the numbers based off Earth (I copped out by saying that Earth was created artificially in the future based off Kímera), but they're not entirely consistent as a whole. Fortunately I'm not so incompetent astronomy-wise to think those two terms are the same, though sometimes I confuse the two. (Hey, I haven't studied astronomy for years [:3])

Re: Is this a realistic conastronomy?

Posted: Fri 01 Dec 2017, 03:31
by Axiem
Ultimately, if you want a system to be "realistic", then you should try to make the numbers be as consistent as possible. But you can also ignore as much as you like (plenty of authors have!), and no one will think the lesser of you. Well, I won't at least ;)

Re: Is this a realistic conastronomy?

Posted: Sat 02 Dec 2017, 16:00
by Illuminus
Okay, thanks!