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AniGa
Observer
Topic Author
Posts: 4
Joined: 16 Dec 2016

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

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?

Greets,
AG

Hornblower
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Posts: 459
Joined: 02 Nov 2016
Location: International Space Station
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### How can I tell how long a day is on a planet?

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.
"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." - Douglas Adams

AniGa
Observer
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Joined: 16 Dec 2016

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

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

Hornblower
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Location: International Space Station
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### How can I tell how long a day is on a planet?

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.
"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." - Douglas Adams

Destructor1701
Astronaut
Posts: 47
Joined: 07 Nov 2016

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

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
Observer
Topic Author
Posts: 4
Joined: 16 Dec 2016

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

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.

Greets,
AG

Cirax
Space Tourist
Posts: 20
Joined: 30 Jan 2017
Location: PV Telescopii

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

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
My work for SE:
Textures for the solar system bodies:Click Here
Catalogs of binary stars, brown dwarfs, black holes and neutron stars (already in official SE).

Xoran
Pioneer
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Joined: 17 Jan 2017
Location: Copenhagen, Denmark

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

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
Space is too big to understand, so do not try to understand.

somsoc
Observer
Posts: 5
Joined: 10 Feb 2017

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

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?

Watsisname
Science Officer
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Location: Bellingham, WA

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

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.

Pepethecat
Observer
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Joined: 05 Feb 2017

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

It says Rotational Period in it's description.
Do not go gentle into that good night, Old age should burn and rave at the close of day; Rage,rage against the dying of the light.

Xoran
Pioneer
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Joined: 17 Jan 2017
Location: Copenhagen, Denmark

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

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.
Space is too big to understand, so do not try to understand.

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