<p>The Earth rotates daily about an axis. This axis of rotation intersects the surface of the Earth at the north and south poles. Imagine a plane that is normal to the axis of rotation and lies halfway between the north and south poles. The equator is the intersection of this plane and the surface of the Earth.</p>

<p>Meridians, or lines of longitude, go from pole to pole along a great circle. The Prime Meridian is simply the meridian that we have deemed to be the zero degrees line of longitude. This was an arbitrarily choice. (The French, for example, argued that the Prime Meridian should pass through the Observatory of Paris.)</p>

<p>Imagine going from the south pole to the north pole along the Prime Meridian. The Prime Meridian ends at the north pole. Continuing in the same direction takes you along the 180th degree longitude line. This means that if the Earth was a perfect sphere, the length of the equator would be exactly twice that of the prime meridian.</p>

<p>The Earth isn't a perfect sphere. The Earth's rotation gives the Earth a slight equatorial  bulge. The equator (at sea level) is about 21 km further from the center of the Earth than is the north pole. This means the Earth's equatorial circumference (40075 km) is about 67 kilometers longer than the Earth's meridional circumference (40008 km).</p>

<p>That this is a nice round number is not a coincidence. The original definition of the meter was one ten millionth of the distance at sea level between the equator and the north pole. A prototype metre bar was created based on initial estimates of this distance. It turned out that this initial estimate was a bit off, and by then it was too late to redefine the meter to match these better measurements.</p>

CC BY-SA 3.0
2016-10-24T12:02:59.323Z
2016-10-24T12:02:59.323Z
David Hammen
<p>i just want to ask in earth what  the difference between Equator &amp; Prime Meridian &amp; also want to know is it same distance Equator &amp; Prime Meridian?</p>

<p><a href="https://i.sstatic.net/cQqUF.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cQqUF.jpg" alt="enter image description here"></a></p>

CC BY-SA 3.0
2016-10-24T09:37:54.370Z
You mean length, not distance?
gerrit
CC BY-SA 3.0
2016-10-24T10:05:33.777Z
You also ask "what the difference between Equator & Meridians".  The quickest way to understand that is to look at your diagram - the meridians all pass through ***the same points***. (The poles,) The "equators" are totally different, they are like **slices**.  The meridians are all the same length.  The "equators" are all different as you go up and down, see?
Fattie
CC BY-SA 3.0
2016-10-24T12:39:17.080Z
Look up definitions.
Carl Witthoft
CC BY-SA 3.0
2016-10-24T12:43:03.850Z
@JoeBlow, circles of constant latitude are called parallels. Only the 0th parallel is called the equator.
Mike G
CC BY-SA 3.0
2016-10-24T12:51:37.203Z
hi @MikeG - sure thing, that's why I said "equators" in quotes.  it's a pedagogic device.
Fattie
CC BY-SA 3.0
2016-10-24T16:52:24.680Z
I'm voting to close this question as off-topic because it isn't about astronomy.
HDE 226868
<earth>
Is it same distance Equator & Prime Meridian?
RANSARA009
# Is it same distance Equator & Prime Meridian?

(Asked by: username_0 on 2016-10-24)

i just want to ask in earth what the difference between Equator & Prime Meridian & also want to know is it same distance Equator & Prime Meridian?

[![enter image description here](https://i.sstatic.net/cQqUF.jpg)](https://i.sstatic.net/cQqUF.jpg)

**Tags:** earth

> **Comments:**
> **username_1**: You mean length, not distance?  
> **username_2**: You also ask "what the difference between Equator & Meridians".  The quickest way to understand that is to look at your diagram - the meridians all pass through ***the same points***. (The poles,) The "equators" are totally different, they are like **slices**.  The meridians are all the same length.  The "equators" are all different as you go up and down, see?  
> **username_3**: Look up definitions.  
> **username_4**: @JoeBlow, circles of constant latitude are called parallels. Only the 0th parallel is called the equator.  
> **username_2**: hi @username_4 - sure thing, that's why I said "equators" in quotes.  it's a pedagogic device.  
> **username_5**: I'm voting to close this question as off-topic because it isn't about astronomy.  

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## 1 answers

### Answer by username_6 on 2016-10-24. Score: 3 | Accepted answer

The Earth rotates daily about an axis. This axis of rotation intersects the surface of the Earth at the north and south poles. Imagine a plane that is normal to the axis of rotation and lies halfway between the north and south poles. The equator is the intersection of this plane and the surface of the Earth.

Meridians, or lines of longitude, go from pole to pole along a great circle. The Prime Meridian is simply the meridian that we have deemed to be the zero degrees line of longitude. This was an arbitrarily choice. (The French, for example, argued that the Prime Meridian should pass through the Observatory of Paris.)

Imagine going from the south pole to the north pole along the Prime Meridian. The Prime Meridian ends at the north pole. Continuing in the same direction takes you along the 180th degree longitude line. This means that if the Earth was a perfect sphere, the length of the equator would be exactly twice that of the prime meridian.

The Earth isn't a perfect sphere. The Earth's rotation gives the Earth a slight equatorial bulge. The equator (at sea level) is about 21 km further from the center of the Earth than is the north pole. This means the Earth's equatorial circumference (40075 km) is about 67 kilometers longer than the Earth's meridional circumference (40008 km).

That this is a nice round number is not a coincidence. The original definition of the meter was one ten millionth of the distance at sea level between the equator and the north pole. A prototype metre bar was created based on initial estimates of this distance. It turned out that this initial estimate was a bit off, and by then it was too late to redefine the meter to match these better measurements.


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