year, day length

sozme

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Hello all, I am trying to figure out how to calculate the year and day length from the set of data I've attached. Some sci fi worldbuilding calculators I have tried seem to not be functioning properly. I was wondering if someone could give me some guidance here?
 

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Hi,

As far as I can see from what you've provided you can't. It lists these things in the table as unknown. If you knew the rotational velocity you might be able to calculate the length of the year.

Cheers, Greg.
 
I concur. As the star is somewhat more luminous than Sol it's probably a bit more massive, although this isn't certain, and as the planet is a bit closer - quite a bit, going to be warm - I would guess the year will be quite a bit shorter.

Day length? Totally irrelevant. Not to the inhabitants, but from the point of view of orbital dynamics. You can spin it just about any speed you want, axis at any inclination from the ecliptic, any number of moons, and it won't change the stability of the basic gyroscope.
 
Day length? Totally irrelevant. Not to the inhabitants, but from the point of view of orbital dynamics. You can spin it just about any speed you want, axis at any inclination from the ecliptic, any number of moons, and it won't change the stability of the basic gyroscope.

Intersting thread...as a complete buffoon at science (and others things in this life too, sadly:)) I am very curious about one aspect of your answer, chrispenycate, and have an open and uninformed question...would the rate of speed of the planet's rotation, and the inclination of the axis toward the sun, not have some effect on the types of life that would evolve, and become established, on a planet?

What I mean is, if a planet had a remarkably slow rate of rotation (from a planetary perspective of scale), the side of the orb away from the sun at any given moment would have very long periods of darkness, and colder temperatures. And if the rate of inclination is extreme, you could have parts of the world that were very cold, and parts very warm (all depending on the proximity to the sun, and its warmth). If either of these two factors varied (rotational speed, or rate of inclination) the conditions could/would be dramatically different than the examples I mentioned, and I would think would allow for different sorts of life to evolve. Does any of this make sense? And if it does, wouldn't that make a difference to the native inhabitants of the world (or off-world species who might consider colonizing a world)? Anxious to hear answers from the more scientifically inclined! :)
 
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If the rotation is very slow then you get massive storms and winds as the energy from hot and cold side try to equalise. The worst is rotation equal to a year. That might be uninhabitable.

Rotation and tilt are completely separate issues and separate from orbital period (year) which is pretty much Kepler's 3rd law,
http://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion

Year = Squareroot ( (radius cubed) * 4 * (Pi squared) / (G *(Star Mass + Planet Mass)) )
G is the universal gravitational constant
Radius is distance of planet from Sun. For elliptical orbit semi-major axis of the ellipse.

You can't have much more temperature differential than we have if there is an atmosphere as the atmosphere will redistribute the heat to the colder parts. This mostly is what makes weather. Also of course heat causing water to vaporise and form clouds.

Coriolis forces increase as rotation increases and these create overlaid structure in the weather such as Jet Streams in the upper atmosphere. I think!
 
My personal planet/star calculations that live in my 'Star system design' Excel sheet would give your planets orbit at roughly 0.7 of an Earth year, or in Sol days somewhere in the region of 257 days. The formulas I use are wot Ray said.

I also get a basic temperature centred around 18 C or 64 F - but that is just assuming a planet is a body with an albedo of 0.3 (approximately the same as the Earth). Actually that's really very warm. By the same very rough calculations that I use, the Earth's basic temperature comes in at -15 C - and it is the Greenhouse effect that gets the average temp to a habitable average of about 13-18 deg C. If we to add this Greenhouse effect to your planet that would give you an actual average temperature of 52 deg C. Which I might argue is generally pretty inhospitable for Terran-like life.

You can of course play about with the albedo to lower that temperature - an albedo of 0.5 gets you a bit cooler (basic gets you minus 10C, + Greenhouse will give you about around +20C). So then you have to have the right 'stuff' in your world - at least half pure white ice I suppose!

EDIT - oh and there's nothing stopping you going 'SHAZAM' and saying that the Greenhouse effect of the planet is way below that of Earths. For many reasons, atmospheric calculations are complicated. But even adding a little to your 18C still makes the planet pretty warm in my book...

As for day length. It's up to you as Chripenycate says. Rotational speed and axial tilt of the planet is not linked in any way with the orbital characteristics. Have whatever suits you.
 
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Here are my new variables
Ok, I calculated the orbital period (but I am not sure it is correct.

To be clear, in my story, humans only visit this world. I'm not sure that these variables are correct, again, a high school science teacher I paid came up with most of these.

Is my calculated orbital period correct? (I double checked it, so unless I had my units wrong)
Do you think that temperature range seems incorrect given the other variables just by eyeing it?

The orbital period is enormous... a planet whose year is over 300 earth years? But its supposed to orbit close to the star? I dont know seems like I might have this wrong.
 
View attachment 22192

Here are my new variables
Ok, I calculated the orbital period (but I am not sure it is correct.

To be clear, in my story, humans only visit this world. I'm not sure that these variables are correct, again, a high school science teacher I paid came up with most of these.

Is my calculated orbital period correct? (I double checked it, so unless I had my units wrong)
Do you think that temperature range seems incorrect given the other variables just by eyeing it?

The orbital period is enormous... a planet whose year is over 300 earth years? But its supposed to orbit close to the star? I dont know seems like I might have this wrong.


I get 0.45 Earth years or 165 (ish) days for a planet that close to the star. It does look like you have the units wrong. Neptune in our Solar System orbits at about 30 AU and it zips by in 164 years. To have a planet orbit a star once every 300 years I'd think you'd have to place it in orbit at about 41 AU from the star.

I also calculated the temperature and ignoring factors like the Greenhouse effect and making assumptions about the albedo of the planet...

...actually I can give you a range depending on the albedo (I make other assumptions but that's the biggest one.):

Albedo --------------Temperature (F)
0.1 ------------------130
0.2 ------------------113
0.3 ------------------94
0.4 ------------------74
0.5 ------------------50

(Edit - I put the dashes in because the forum software is removing the formatting spaces.)

Earth has an albedo that is roughly 0.3. To get a 'correct' temperature of your planet you will need to hypothesis what size of greenhouse effect you want. In my rough calculations Earth has a greenhouse effect that adds 33 degrees C or 91 degrees Farhenheit.

Thus adding that to the above, this implies to me that your planet is in serious danger of overheating - to make it habitable for Terrain life (if that is how you envisage it) then the albedo needs to be pretty high. On the other hand you might want a baking hot desert world that is a bit like an oven...
 
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Thank you... by any chance, do you have a copy of this excel sheet you use to auto calculate these variables? I've been looking for something like that.
 
Thank you... by any chance, do you have a copy of this excel sheet you use to auto calculate these variables? I've been looking for something like that.

The excel sheet I use is my own personal 'concoction' so I didn't 'design' it to be user-friendly :) i.e. I understand what's happening, but if you were to take a look at it, it probably confuse you a whole lot more!

I will try over the weekend to give it a shot at redesigning it, so that it should be much easier for someone else to use it. And also put in exactly what I did - so that you can compare and contrast with other calculations. But it depends on what's happening with me (always as ever a million and one things hanging over my head) so I might be a bit tardy!
 
Orange stars are bad news (planets have to be too close and then flares sterilise them). But if it's a lifeless steamy rock you just surveying it's OK.
 
For the original set of figures, you still have an unknown variable that makes a difference; the star's age. As an example, in about 3 billion years Sol will have around 1.1 times its present luminosity (AFAIK) because of the effects of stellar evolution.
 

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