# Why do we say Earth rotates from west to east?

It is said that Earth rotates from west to east. I take this as

Earth's western hemisphere moves towards the Eastern hemisphere when seen from the frame of reference of pole star.

Now I can also say that,

Earth's Eastern hemisphere moves towards the western hemisphere when seen from the frame of reference of pole star

So can't I say then Earth rotates from east to west?

When we say Earth rotates from west to east we don't say a point on earth moves from its west to its east. We just say Earth moves from west to East. Now what is west and East for Earth? My knee-jerk is that Earth's west means the western hemisphere. Then it is not wrong to say Earth moves from East to west as the Eastern hemisphere always move towards the western hemisphere.

P.S: The question was originally asked at https://gis.stackexchange.com/q/178685/66197 The discussion in comments over there might be useful.

• Because east and west are defined by the rotation of the Earth? WRT your example sentences, it's perfectly possible to say things that aren't correct :-) Thought question: if there was a planet that didn't rotate, would it have an east or west, or FTM north or south? Jan 30 '16 at 5:34
• @jamesqf Are the north and south pole defined w.r.t. East and west--which are defined by earth's rotation? I thought that East and west are defined w.r.t. to the north pole because North pole is defined as the pole towards the pole star. Jan 30 '16 at 5:46
• Because east and west are defined by the rotation, as are north and south. If you had a planet which didn't rotate at all, there'd be no way to distinguish any directions. And no, I don't have references. It just seems obvious. Jan 31 '16 at 6:37
• The eastern and western hemispheres are nothing but arbitrary cultural descriptions. There's nothing physical that defines them. Not even the longitudes, which are arbitrarily defined as starting at Greenwich - if that was the case, part of Britain would be in the eastern hemisphere, part in the west. Feb 1 '16 at 19:23
• This is really a question for EL&U! The word "East" is derived from a term meaning "dawn" (etymonline.com/index.php?term=east) and "west" from a word meaning "evening" (etymonline.com/index.php?term=west). Apr 11 '17 at 0:44

Your confusion arise from the definition of East and West hemispheres. That's an arbitrary and confusing definition. Because East and West are relative directions. Meaning they depend on the position were they are specified.

East and West come from the proto-germanic languages, where East means dawn and West means evening. Therefore, East from any given point is roughly the direction at which the sunrise happen. And West is where the sunset happens.

That's why the east/west hemispheres definition is confusing, because if you are in the middle of the pacific, the Western hemisphere is towards the East... confusing.

So let's forget about East/West hemispheres, and consider the East/West cardinal directions. Where East is 90° to the right of North and West 90° to the left of North. These directions keep the original spirit, on which East points roughly to the sunrise, and West to the sunset. Let's also forget about clockwise and counterclockwise, because that depends on where are you looking from. If you are on top of the North pole it will look like Earth is rotating counterclockwise, but from the top of the South pole it will be clockwise.

Now, when we say that Earth rotates to the East, we mean that each point on the surface is moving to the East of that point.

The following figure taken from pulauubinstories.com will help clarifying the point:

In the figure is clear that the fact that sunrise happens to the East is because we are moving in that direction. At dawn, as we move Eastwards we enter in the sunlit side of Earth, producing the sunrise. And as we keep moving Eastwards during the day, we enter in the night side of Earth, leaving the sunshine and the sunset to the West.

Therefore, as East means "dawn" it follows (basically by definition) that Earth rotates to the East.

Imagine you can fly ignoring wind, gravitation and other forces. You are exactly on the rotation axis looking down the Earth on its North side. You'll see the Earth turning counter-clockwise. But If you look at the same but in South Hemisphere, the Earth is turning clockwise. This is just a convention and it depends on your point of view.

Nevertheless, If we look at the Earth from outside in the way that the North Pole is up and South Pole is down, you are going to see West on your left hand and East on your right hand. Always, does not matter how much you rotate. It does not depend on your point of view.

All this works as long as we set the North Pole up and West is always on its left. It is illustrtated in this gif.

• Earth also rotates west to east on the southern hemisphere. This is not a convention. Jan 30 '16 at 14:36
• Agree with Christoph. Alejandro's example works just as well if you're flying above the equator, no matter which way is "up" for you.
– TTT
Jan 30 '16 at 15:26
• You are right. Edited. Jan 30 '16 at 17:06
• But even by looking from above the north pole Earth's Eastern hemisphere moves towards the western hemisphere. That is Earth rotates from east to west. Jan 31 '16 at 6:19
• @user31782: Not unless you're looking on a timescale long enough to involve plate tectonics. On human timescales, the surface of the Earth is fixed. Feb 1 '16 at 19:26

The Earth rotates from west to east or counter-clockwise. You can do simple experiment. put your face towards the polar star and stretch your hands. Your head shows North (towards polar star) and your left hand points towards west, your right hand points towards east and your back head points towards South. The sun rises in the East - from the direction of your right hand and sets in the west - towards your left hand. Assume the sun is fixed in space because with respect to the Earth rotation speed the Sun's rotation is very small. Hence it is the Earth which is rotating and is the reason for sunrise and sunset. If the sun rises in the east and sets in the west, then the Earth should rotate in the opposite direction from west to east (anti-clockwise).

• Then my right hand is the East of Earth and the left hand is west of Earth. Now since the Earth is rotating counter-clock wise my right hand is rotating towards left that is Earth's East is rotating towards Earth's west. So doesn't it mean that Earth rotates from east to west. Feb 1 '16 at 5:25
• I know what you mean. Your axis of rotation determines that. According to your assumption the axis of rotation is perpendicular to longitude lines. That is why you thought it wrongly. The axis of rotation of the Earth is from North to South with a little tilt - obliquity. You can look at this example: en.wikipedia.org/wiki/Rotation#/media/… Feb 1 '16 at 17:33
• I am taking the axis of rotation just as shown in the Wikipedia image. If Earth's west is rotating towards East then at the same time Earth's East is rotating towards West. Feb 2 '16 at 3:52
• You can't rotate a rigid body in two opposite direction simultaneosly. Take an apple and rotate it. It rotates only in one direction at the same time. For Earth also there is only one direction of rotation at a time. That is from west to east. Feb 2 '16 at 5:43
• I agree that there can be only one kind of rotation--clockwise or anticlockwise. What I am saying is that, west to east doesn't specify whether it is rotating clockwise or anti-clockwise because we can reach East from west bothways, clockwise and anticlockwise. Feb 2 '16 at 6:24

You do realize, that you can only define/name your hemispheres after the directions are defined (and how they are defined) in that reference system?

The Earth from above the Northpole and it's rotation:
For some reason, we call that "East" and it's opposite direction "West":
Now we can pick some arbitrary point/line to slice the Earth into 2 hemispheres and name them according to which side of the slice is in which - previously defined - direction.
Just for fun, let's call it our "prime meridian", so everybody is clear what we are taking about.
(In the end .. it's a sphere. It has no that point to cut or that 2 hemispheres.)
Now put that together in one picture:
What is the vector named the eastern hemisphere moves?
It is East. Period.

It doesn't matter, that at some point(s) in time the eastern hemisphere takes place, where the western hemisphere was.
You cannot change the naming of the direction without rendering the whole naming convention for your hemispheres (and thus all your assumptions) null and naught.

What you are trying to do is just nonsense.

• "What is the vector named the eastern hemisphere moves?" !!? Vectors ain't curved Period. Feb 1 '16 at 12:41
• @user31782 What do you expect me to say. You cannot call the rotation "to the west", simply b/c - by definition - west means sth. different. Take it, leave it, believe us .. or don't. I'm done & don't care any longer :/ Feb 1 '16 at 13:02