How do you measure your speed in space?

Question

I've been wondering, when in a car you measure speed on a speedometer based on the rotation of the wheels. In an airplane you measure airspeed relative to the air. But in space, where there is no road and no air (or pressure) how do you measure your speed? If it's the case where you measure it against a near object, what if there are no nearby objects?

Answer 1

Very good question. You cannot use miles per hour Earth Measurements. Speed over time = velocity just does not work when speed and time are relative variable earth things. The speed it takes light to travel is our only choose in space. Until we can warp time bend space. Science Fiction Stuff that has a way of becoming true. Need help dismantling that allien space craft I want the antigravity generator.

Answer 2

Yes, you are right. Speed or velocity is always relative to an observer. It depends on which frame of reference you are in. If you are thinking about space-ships, let me explain it to you.

How to measure speed of a space-craft on the earth.

Let's say that a space-craft was launched from the earth in the direction of Mars. The space-craft will be launched in the direction of the rotation of the earh. So, lets say its launch velocity was 1km/s. But this speed is relative to the earth, assuming the earth to be at rest. Let us suppose, that the earth itself rotates with a speed of 10 km/s. So, the true speed of the craft = 1 + 10 = 11km/s. This is how the true speed is calculated roughly.

Actually, most spaceships that we've sent into space don't measure their own speed, but we know their speed anyway because we've sent them on the exact orbit that we want, for which we could predict what their speed would be.

As you might be aware, space-explorations are planned keeping in mind the distance and position of the destination. So, you can image, how precise the above calculations must be.

Answer 3

According to Einstein's theory of relativity, all motion is relative, it just depends on what you measure it against. You may think you're sitting still, but you're travelling 1,000 mph with reference to the earth's center, 18.5 miles per second with reference to the sun, 300 miles per second with reference to our galaxy's center, and nearly the speed of light with reference to the cosmic rays hitting our atmosphere. There is no standard reference with which to measure speed.

Since the speed of light is fixed, scientists once thought they could measure speed based on the speed of light. They thought that since earth was speeding through space at least around the sun, that light would travel faster in one direction than the other. However, they discovered that light goes the same speed no matter how fast the object measuring it goes. This flies in the face of reason, but Einstein figured out that the speed of a reference object distorts space and time slightly, enough to make all speed appear relative even though the speed of light is a constant.