How many rotations does Earth make in a year?

[david_uwi]

I think the number of rotations is actually 366 in a year and the orbit takes off one day (though I could be wrong it's starting to make my head hurt). And yes I have been around a loooong time from the days of the qbasic forum on network54.

[STxAxTIC]

Yeah, ya know, I could have avoided the word "rotations" altogether and just stuck to "days" in this title of this thread... you have a point there.

The first thing that helped me wrap my head around this went something like this...

For so-called tidal lock (which thank god we don't have), there would be one long, infinite day, and the notion of "year" is undefined unless you somehow introduce more reference vectors (i.e. directions to stars, cosmic rays).

Next I imagine a different case with one day taking one year to complete. To do this, I keep the earth fixed, i.e. no rotation at all, and then translate it in an orbit around the sun. This will give the apparent view of a sunrise, sunset, etc.

So the trick *just* happened if anyone missed it. We have a case of an earth that does *not* rotate, but it experiences a single day *anyway*.

Now build from there. Suppose we "tune in" exactly one rotation of the planet as we drag it around the sun. Fine, like before, I translate it around a rough circle while twisting it once. As viewed from earth, there are now *two* days, but we only forced *one* rotation.

This off-by-one error goes all the way up to 365 +/- 1. The sign is determined by whether or not the rotation and revolution axes are in agreement.

[doppler]

For so-called tidal lock (which thank god we don't have)

Somewhat wrong.  In our part of the galaxy there is tidal lock.  It's the moon.  If the moon's rotation was not locked to earths rotation we would get to see the scared backside.  If you compare front (earth facing) to backside.  The moon is really scary.  Consider this, any hits on earth facing side had to get near earth at one time in the meteor orbit.  The backside just get hits, and is the likely target of all meteors.

[doppler]

all the other planets ......We have never yet seen Pluto complete a full "year".

So I'm a nerd...

J

Well you are behind in the times.  Pluto is no longer a planet and just a name of a dog now.  We have 8 planets, and a big icy rock.  Don't start up about Pluto is really a planet and not a rock.  Out beyond Pluto's orbit there are dozens of bigger rocks found orbiting the sun.  They are all numbered and not named.  AND not planets.

I became a BIGGER nerd than you now.
Get the nerd meter out and let's measure them.

[STxAxTIC]

Have the last word doppler, but (in the words of Joe Biden) c'mooooon man. Emphasis on "moooooon", because nobody was talking about the moon when it comes to counting days on earth. What you did is cherry pick my words, and call them "Somewhat wrong." (full quote), and then proceed to write the wrongest possible thing I can imagine on this topic, "In our part of the galaxy there is tidal lock." Just nope.

I appreciate what you add to the discussion about the moon, which happens to be in tidal lock with the earth. Excellent.

To be clear though, I was saying that if the earth had a locking relationship with the sun, life would be pretty tough, only possible near the perpetual twilight.

[OldMoses]

This off-by-one error goes all the way up to 365 +/- 1. The sign is determined by whether or not the rotation and revolution axes are in agreement.

In that case, Venus and Uranus would be (+), with all the others being (-), they being the only planets who's rotation is retrograde with respect to their orbits. Uranus is a little odd with its axial inclination being less than a degree from the ecliptic. It may not have been retrograde at some point if it has wobbled.

[doppler]

@STxAxTIC Well if the earth was locked with the sun, we would not have this conversation.  Half the planet would be roasting the other half frozen.  Only a thin band at the equator could be called normal (night/day differential part).  It wouldn't be the same.  Maybe I did go off skew a bit.  But the conversations did involve earth/venus/sun/that ninth piece of rock.  It just got a little silly there.

[TempodiBasic]

Hi Doppler
with the dark side of moon and your affirmations about it NOW we know that aliens couldn't have their secret base there!
So the moon is our lighting rod of meteors.... :-) We are so lucky

Pluto is the dog of mickye mouse, but where is the Xplanet in our solar system? https://en.wikipedia.org/wiki/Planets_beyond_Neptune#Planet_X

[doppler]

Xplanet

Ya, just had to go there didn't cha.

[johnno56]

... and don't forget about 'daylight savings'... Missed that one several times for our wall clock... (analogue... who knew, right?)

[TempodiBasic]

But if you agree we can escape frome earth and go onto Vulcano the first intramercurial planet.