For Questions That Don't Merit Their Own Thread

[darthgently]

1 hour ago, farmerben said:

How many times does the Earth rotate in one year?

I'm not sure if the answer is 364 or 366.  If you had a planet that didn't rotate at all one day would equal one year.  Venus is very interesting in this regard.

365.24, thus the leap years every 4 years dropping a day in February.  Then some leap seconds thrown in on some schedule

[tomf]

2 hours ago, farmerben said:

How many times does the Earth rotate in one year?

I'm not sure if the answer is 364 or 366.  If you had a planet that didn't rotate at all one day would equal one year.  Venus is very interesting in this regard.

It is 366.25.  The sidereal day (compared to fixed stars) is 4 minutes shorter than the mean solar day.

Your example of a non rotating planet would have a day the length of the year, but the sun would appear to be travelling in the wrong direction.

Edited January 24 by tomf
More precision

[darthgently]

56 minutes ago, tomf said:

It is 366.25.  The sidereal day (compared to fixed stars) is 4 minutes shorter than the mean solar day.

Your example of a non rotating planet would have a day the length of the year, but the sun would appear to be travelling in the wrong direction.

365.24

[farmerben]

Every day you do one rotation plus a little extra.  The extras add up to a full rotation in one year.

[darthgently]

26 minutes ago, farmerben said:

Every day you do one rotation plus a little extra.  The extras add up to a full rotation in one year.

Depends on reference frame I suppose.  Works either way

[Jacke]

On 1/24/2025 at 6:12 PM, farmerben said:

How many times does the Earth rotate in one year?

I'm not sure if the answer is 364 or 366.  If you had a planet that didn't rotate at all one day would equal one year.  Venus is very interesting in this regard.

Depends on which "day" and which "year".

https://en.wikipedia.org/wiki/Day
https://en.wikipedia.org/wiki/Year

If you mean mean solar day and Tropical year:
> The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds, using the modern definition^[13] (= 365.24219 d × 86400 s). The length of the tropical year varies a bit over thousands of years because the rate of axial precession is not constant.

[monophonic]

On 1/26/2025 at 7:07 AM, Jacke said:

Depends on which "day" and which "year".

https://en.wikipedia.org/wiki/Day
https://en.wikipedia.org/wiki/Year

If you mean mean solar day and Tropical year:
> The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds, using the modern definition^[13] (= 365.24219 d × 86400 s). The length of the tropical year varies a bit over thousands of years because the rate of axial precession is not constant.

"Day" and "rotation" are not synonymous, and use of the latter does imply sidereal day. That is where @farmerbens question becomes interesting. Indeed if the Earth did not rotate at all around its axis, we would have negative one days in a year. Negative to account for the opposite movement of the sun. If Earth was tidally locked to the Sun, so we had no day/night cycle, Earth would rotate one full rotation around its axis in a year. Add to this the 365 and a bit days we observe, and the answer is indeed one more rotations than solar days. Or 366.24219*360°=131 847,1884°.

[Fizzlebop Smith]

I have been trying to envision a Celestial composition that produces a semi-locked planet.

 

I am trying to write a work of fiction where the planet has a day / night side with a terminus at the prime meridian.

 

However... I want the Sun to move in relation to observers on the planet.

I want the sun to appear to take an elliptical path through the sky. As you go from terminus to pole .. the sun goes from low on horizon to overhead.

The issue is a tidally locked planet has not observable movements for the sun. So I would need an axial Wobble? 

This is probably a dumb question to those with knowledge of celestial mechanical, but it's driving me a little loopy. 

I can just wave hands since it's a work of fiction and atmosphere and life would not be present.. but it still drives me up the wall in those moments of boredom.

Essentially I need a planet with a variable tilt that is tied to rotation. 

Was this articulated in a way where it makes sense what I'm asking? If not just write it off as babbling of a GM wanting to record the campaign one day.

[magnemoe]

1 hour ago, Fizzlebop Smith said:

I have been trying to envision a Celestial composition that produces a semi-locked planet.

I am trying to write a work of fiction where the planet has a day / night side with a terminus at the prime meridian.

However... I want the Sun to move in relation to observers on the planet.

I want the sun to appear to take an elliptical path through the sky. As you go from terminus to pole .. the sun goes from low on horizon to overhead.

The issue is a tidally locked planet has not observable movements for the sun. So I would need an axial Wobble? 

This is probably a dumb question to those with knowledge of celestial mechanical, but it's driving me a little loopy. 

I can just wave hands since it's a work of fiction and atmosphere and life would not be present.. but it still drives me up the wall in those moments of boredom.

Essentially I need a planet with a variable tilt that is tied to rotation. 

Was this articulated in a way where it makes sense what I'm asking? If not just write it off as babbling of a GM wanting to record the campaign one day.

The moon does tilt a bit relative to earth but its 10% something, having the sun move 30 degree would probably work but I guess you need an decent elliptical orbit to start with, or having an decent sized moon, probably closer but it could be smaller.  If planet is pretty young it also helps.