# Space Speed

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So, a car against asphalt it’s pretty easy determinining the speed.
But when someone says a spaceship, for example Voyager, travels at about 61.5 kkm/h. What speed are we comparing against? According to Google, Earth rotates at the equator at about 1.5 kkm/h. So if we said that we compare Voyager speed vs Quito speed and assuming angle of Voyager vs Quito is 90 degrees then that should be +- 1.5 kkm/h?
And Earth itself is also according to Google running around the sun at a clip of about 107 kkm/h so that would mean that at some points Voyager is doing -40 kkm/h vs Earth.

Just standing “still” in the Universe some shit would be moving really really fast compared to me so where do we flip reference points?

edit: lost a couple of ks

In: Planetary Science

Your main problem is thinking of movement of space objects in linear way. In fact it is not.

Everything in space are controlled by forces of gravity. Every object orbits something – mostly in elliptic or circle orbit. [Read about Center of Gravity ]( https://en.m.wikipedia.org/wiki/Center_of_mass#Center_of_gravity) To escape gravity of something, there is equations on [Escape Velocity](https://en.m.wikipedia.org/wiki/Escape_velocity).

That velocity is actually 3-dimensional and all summed up creates a vector of movement. Depending on velocity we figure out gravity of what object we’ve escaped and in gravity of what object we are entering now. Our vector of movement would define how we gonna orbit that new object.

So basically, Voyager escaped Sun’s gravity, but vector of movement is different from vector of movement of Earth. Also, from the perspective of black hole in the center of our galaxy – some planets are going faster than Sun (get forward of Sun) , then slower than Sun (get behind of Sun)

Also, play Kerbal Space Program, where you could realistically launch stuff into cosmos.

It’s all relative, and Voyager’s speed of 61.5k km/h is meaningless without saying what it is measured relative to.

Because Voyager 1 and 2 are on a trajectory out of our solar system, it is usually given as speed from the point of view of our sun. This is also what [Wikipedia says](https://en.wikipedia.org/wiki/New_Horizons#Speed) (although not on the page about Voyager 1):

>*Voyager 1*, traveling at 16.985 km/s (61,146 km/h; 37,994 mph) relative to the Sun

You kind of have the gist of it. All movement is relative to some frame of reference. For a probe like Voyager 1 in interplanetary space we’re measuring its speed relative to the sun.

For all but a very few man-made things, the reference is going to be what it’s orbiting about. This is most often Earth, but can be the Sun, or another planet.

But you have asked about one of the exceptions — Voyager. Since they are above the escape velocity from the Sun, aren’t in orbit around the sun. Non the less, I suspect the speed is in reference to the Sun since we tend to like to think our solar system is somehow exceptional.

Since the Voyager spacecraft now basically in interstellar space, referencing their speed to the center of our galaxy might be more appropriate:

https://astronomy.stackexchange.com/questions/53615/space-travel-relative-to-solar-systems-movement-through-space#:~:text=The%20Voyager%20spacecraft%20are%20pretty,the%20center%20of%20the%20galaxy.

It’s compared against the sun. The sun is considered the centre for all things in the solar system. It helps because everything nearby like the voyager probe *is* centred around the sun.

And yes the sun is moving relative to our galactic nucleus in a direction. But that can be considered our 0, because our entire solar system is moving at a close speed in the same direction. And so was the voyager before it took off in the rockets.

So it’s like we are all inside a train. If a ball rolls on the floor of the train, it’s easier to talk about the speed of the ball relative to the train, than talk about the speed relative to a lamp far away.

Generally speaking, we would never flip references because it would just cause confusion.