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AniGa
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How can I tell how long a day is on a planet?

16 Dec 2016 07:47

Hi there.

Basically, Space Engine only tells me about the orbital period, the rotation period and the solar day (Which is different from a day in general terms, right?) of a planet.

How can I tell how long a plain ol' day is on a planet?


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AG
 
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Hornblower
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How can I tell how long a day is on a planet?

16 Dec 2016 08:22

     AniGa, depends on your definition of a day. If a day to you mean 24 hours, then use the solar day. A solar day is determined (correct me if I'm wrong) by the time it takes earth to rotate once in reference to the sun. This is slightly longer or shorter (based on which way the planet is rotating) than a rotational period, which is a rotation in relation to the stars. It's different because when the earth rotates once, it would have also traveled along its orbit too, so the angle of a line from the earth to the sun would change a little to. This means that the time of each solar noon would happen at a different rate than noon for a star outside the solar system. Obviously this difference would add up, and they do. That's why constellations appear at slightly different places each day. I hope I explained this well enough.

     If you mean to find the length of the day as in sunrise to sunset, that is not constant across a planet. For example, a "day" in Antarctica would be 6 months.
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AniGa
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How can I tell how long a day is on a planet?

16 Dec 2016 09:38

What I mean is how to determine a planet's equivalent to our Earth's good old 24-hour-day.
And from what you say, it seems that the length specified under solar day IS, in fact, exactly that.
Unless, of course, I misunderstood you.


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AG
 
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How can I tell how long a day is on a planet?

16 Dec 2016 11:52

AniGa wrote:
What I mean is how to determine a planet's equivalent to our Earth's good old 24-hour-day.
And from what you say, it seems that the length specified under solar day IS, in fact, exactly that.
Unless, of course, I misunderstood you.


Greets,
AG

You may have misunderstood me. I was just saying it all depends which type of day you follow (most people follow a solar day). But yes, it does convert a planet's day into earth days if it's over 1 earth day. If it's less than one earth day, it will give the solar day in hours.
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Destructor1701
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How can I tell how long a day is on a planet?

16 Dec 2016 14:44

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It's called a Solar Day because that's how long the Sun takes to get to the same angle in the sky again after a full rotation of the Earth.
 
AniGa
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How can I tell how long a day is on a planet?

16 Dec 2016 23:05

Alright, thank you!
Just wanted to make sure that I don't misunderstand the information given to me.
Trying to look for a neat, interesting planet that would be suitable for human life as-is. :D


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AG
 
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How can I tell how long a day is on a planet?

01 Feb 2017 06:48

Sometimes the solar day could be some confusing, for example in Mercury the rotational period is 58.7 days but it's solar day is 176 days!  That's because is captured in a resonance orbit of 3:2
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How can I tell how long a day is on a planet?

26 Feb 2017 09:37

AniGa wrote:
Source of the post Alright, thank you!
Just wanted to make sure that I don't misunderstand the information given to me.
Trying to look for a neat, interesting planet that would be suitable for human life as-is.

Well good luck finding a potentially habitable planet without toxic levels of SO2 or CO2 in the air ;)
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somsoc
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How can I tell how long a day is on a planet?

27 Feb 2017 13:59

On this subject, I'm wondering if there's a way to tell what time it is locally if you're on an object's surface. For example, if the solar day is 48 hours, which hour is it currently?
 
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How can I tell how long a day is on a planet?

27 Feb 2017 14:18

Sadly I don't think there's an easy way to tell this.  You'd pretty much have to figure it out from scratch.  Like, if the solar day is 48 hours, then you can say the Sun is at its highest point in the sky at solar noon, and will rotate through 360 degrees of azimuth angle in 48 hours.  So each hour past solar noon corresponds to an extra 7.5 degrees that the Sun has moved from there.
 
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Pepethecat
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How can I tell how long a day is on a planet?

11 Mar 2017 08:17

It says Rotational Period in it's description.
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How can I tell how long a day is on a planet?

14 Mar 2017 11:29

Pepethecat wrote:
Source of the post It says Rotational Period in it's description.

Solar day is more accurate, since when a object has rotated once, it has also moved in relation to the object it orbits. Solar day accounts for that, rotational period doesn't.
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