Why is Earth's orbital plane 0?

Question

The plane in which the orbit of a planet lies is referred to its "orbital plane". Each of the nine planets has its own orbital plane. The term "inclination" refers to the angle at which the orbital plane is tilted with respect to a plane that is the standard of reference. Notice that the inclination of the Earth's orbital plane is 0. Explain why.

Honestly I have no idea why the plane is 0. My only guess is that the plane is not tilted, which would make it 0, but that does not seem like it would be the answer.

Answer 1

Since we +_live+_ on Earth, it is only natural to assume that the orbital plane, indeed everything about the planet should be the benchmark for this solar system.
It shall remain so until some more powerful extra-planetary being says that things will be different.

Answer 2

Our plane is tilted when compared to the sun's equatorial plane.

It is just that our plane is the first one we identified (in fact, early astronomers thought it was the plane of the Sun's orbit, as it went around the fixed Earth).

So we (humans) started counting inclinations from our orbital plane and we never bothered to change it (we would not change unless we found another plane that was more useful as a measurement base).

Actually, what we now use is the "average" orbital plane of Earth over centuries. In 2007, Earth's true orbital plane is 0.0009 degrees from this average. This "wobble" has been known for some time (historic, even) and a good part of it is due to something called "lunation" over a 19 year cycle.

Answer 3

The Earth's orbital inclination is zero, and the inclination is the angle of the orbital plane to the reference standard. So it must be that the Earth's orbital plane is being taken as the reference standard.

Answer 4

Earth's orbital inclination is, by definition, zero, because the reference plane is arbitrarily defined as Earth's orbital plane. This is done because it simplifies astronomical calculations for Earth-based observers.

Answer 5

It's zero because we say it is, just as the Greenwich Meridian is 0 degrees longitude because we say it is, the freezing point of water is 0 degrees Celcius because we say it is, New Year is January 1st because we say it is, and so on. It is simply that there had to be a reference point to relate all other values to, so our orbital plane was defined as that reference.

Answer 6

Our orbital plane is 0 because we live here.
So every other planet's inclination has to be measured from here.
If we lived on any other planet then we could perhaps have different inclinations but it seems better to reference from our point of view.

Answer 7

It also depends on the epoch you refer to. If the epoch is right now, then the inclination is 0. If you use another epoch, such as J2000, than the inclination becomes non-zero by a very small amount. That is because it moves ever so slightly, due to peturbations fro other planets.

Answer 8

Zero degrees is our *referent* so that we can determine all the other planetary inclinations in a positive or negative direction above or below the plane in which we are situated.

This is like a number line or GMT, more than the equator.

Answer 9

It's not. It's just convenient to refer to our orbital plane as the zero reference.

Doug

Answer 10

Because we're from Earth. If we lived on Mars, Mars' orbital plane would be zero. If we were from Saturn, Saturn's plane would be zero.

We measure *everything* with respect to ourselves.