# What speed am I ACTUALLY moving through space?

This question requires mathematical calculations that are beyond my abilities for now…

Say I live on the equator of the Earth, somewhere in say, Mexico. How fast is my body moving through space, when including the speed of the earth in it’s revolution around the sun, it’s rotation, and any other velocities that may apply? There must at least be a maximum and minimum speed…

It’s entirely relative. There is no one answer without giving the point from which an observer is measuring your speed.

The earth rotates at roughly 1000 miles per hour. The earth moves roughly 500 million miles per year, which works out to a speed of about 60000 miles per hour. So it varies between about 59000 and 61000 miles per hour, assuming that the rotational plane of the earth is the same as its orbital plane. That should be the situation that allows for the most variance.

Note that these are very rough calculations, and I’m not making any promises about their accuracy.

You can calculate your speed relative to some other object, there is no absolute speed. You can calculate each one of those numbers (rotation of the earth, earth orbit around the sun, solar system around the Milky Way, Milky Way in relation to other galaxies).

I don’t know the numbers myself.

You have to specify your speed relative to something. There is no fixed point in space against which to measure an absolute velocity.

[Monty Python]Just remember that you’re standing on a planet that’s evolving…
revolving at nine-hundred miles an hour…
[/Monty Python]

The Milky way and associated galaxies are moving with a velocity of about 600 km/sec with respect to the cosmic microwave background radiation. The speed of the earth’s rotation, it’s movement around the sun, the sun’s orbit around the galactic center are all tiny by comparison.

here is the rest of the song. I’ve heard that it is fairly accurate, and IIRC Eric Idle had contacted several astronomers when writing it.

Just for the record, it’s only velocities (rates of travel in a straight line) that cannot be absolutely determined; speeds associated with rotation can, because other forces are involved/generated in travelling along a curved path.

MT, I don’t think that’s true. If you’re in an orbitting satellite the gravitational forces that keep you moving in a curve do not manifest themselves directly to you, you would feel (nor could any measuring machine measure) a net effect or force.

One must always have an inertial frame to talk about speeds or velocities.

Take it with a pinch of salt, IANAPhysicist.

…you would NOT feel…

If I struggle with English so, you should definitely take my physics lightly.

Well yes, but wouldn’t the gravitational forces be one of the ‘other forces’ that I was talking about?

That’s a neat trick.

I don’t know, do I? As I say I’m not a physicist. But I have seen one on TV. The point I thought you were making is that one could determine ones angular velocity as a matter of principal, when in fact (that is, I believe the TV physicist said) this is not the case. Specifically, what with curved space-time and all that (see, I have the jargon), except in Newtonian mechanics, there is no difference between motion a straight line and motion in a curve.

Take another pinch of salt, this is all starting to sound badly wrong now.

the equator doesn’t go through Mexico, huh… so my geography sense is kaput, yeah, I know. Just imagine a point on the equator then, where rotational speed is the greatest.

Choose an object in space (can be an imaginary object) work out how fast it is moving relative to you. Now you are moving the same speed relative to that object, as that object is moving relative to you.
Since the object can be imaginary, then you are moving at all possible speeds, and in all possible directions. It just depends on how you define the observer of your speed. (b.t.w. speed in a given direction is what is called velocity, it’s a scalar, vector thing if you remember the math/physics).
So to get a value for speed that is interesting, you need to choose an observer that is interesting. You have a speed relative to the Earth (nicely shown on your car’s speedomitor when driving).
You have a roitational speed, due to the earths rotation (length of line of latitude at your location in miles / 24 mph)
You have a speed relative to the sun (roughly equal to the circumfrence of the earth’s orbit in mile divided by (365.25 * 24) in m.p.h.)
You have a speed relative to the centre of mass of our Galaxy.

And you have a speed relative to the universal background radiation (thought to be the remnant of the big-bang explosion).

Someone above added the earth’s rotation with its revolution around the sun, but don’t we have to subtract half of one of those figures, since half the time the world must be rotating the opposite to its revolting direction in a calculus sense, or something.
Somewhat hijack: the more interesting query than speed is the path of the earth, or even better the path of the moon throughout space. The moon neer really gets all the way around the earth in a circular or elliptic I mean orbit since the earth has moved on along, so the moon is actually making a kind of regular scribble or corkscrew type path in one plane. But since the sun is moving around the Galactic Center, the moon’s scribble path is carried along somehow and I can’t imagine it in my mind. Also the plane of our planets isn’t in that of the galaxy but is tilted 60 degrees away from it, and moreover, the local stars move up and down in a wave pattern as the galaxy twirls around, which must affect the shape of the path of the moon too. Ie., the solar system tilted sixty dergrees and several nearby stars hump up and down as they make their way with other stars around the whole galaxy. The galaxy is moving some say toward Andromeda galaxy, or the other way around, or both, some say; other time one reads in the data that in any case the entire Local Group is travelling along as part of the total expansion of the universe.
I am assuming as a fixed point from which this strange curve of the moon could be ddrawn to be above the north pole of the earth looking down. It would be a point straight up along a line connecting the south and the north poles, that is, and projected straight “north” way far out about a couple parsecs from the universal zenith or maybe at that zenith itself actually. Which the Zenith would be that point inscribed upon the dome of the universe by a line from the south to the north pole of the earth. However, I know some will not believe in the Universal Zenith (which I just thought up). One proplem would be that old bugaboo of the Precession, and now that I thihk of it, whoops, the fac that the very fact that the earth is moving makes it impossible in principle to talk about making a fixed point from a line extended from the south to the north pole and hitting on the dome of the universe. But couldn’t we then average it all? All the positions that this dot on the Dome would take coud be averaged out and then that’s the point from which we would view the path of the earth. No…that woulnd’t work either since it would be like the perpetual motion machine being impossible. Jeeves, get me a coool cloth to put on my head…

well, there’s really no such thing as a “fixed” point in space, right? Over time, two fixed points in space will change their relative location on appropriate scales, making the initial measurement meaningless, right? Nothing in space stays where it originates from (if space does indeed expand from the alpha).

So how can there be a fixed point in space?

There can’t. That’s the point. You have to define a point to measure your speed against. You have to say, “OK, let’s say that star over there is motionless. I’ll measure my speed relative to it.” It’s not motionless, of course, so your speed will change depending on what point you choose. There is no meaningful answer to your question.

Is the exact center of the universe a fixed point?