Redshift, Earth's orbital speed, and the speed of light

In summary, the Earth has a speed of around 30km/s as it orbits the Sun, with a change of 60km/s over the course of a year. The accuracy of redshift measurements, which measure changes in the wavelength of light, depends on the instrument used, with the best spectrometers able to detect changes as small as 1m/s. Other factors such as the Earth's rotation, orbit, and influence of the moon are also taken into account. The Solar System has an estimated speed of 230 km/s as it moves around the Milky Way, but there is no absolute speed through the universe as all motion is relative.
  • #1
iantresman
67
2
The Earth is moving around the Sun at around 30km/s, a change of 60km/s over the course of the year.
  1. Presumably, measurements of the speed of light would show a redshift up to ±30km/s? Are redshift measurements this accurate?
  2. Likewise, the speed of the Solar System around the Milky Way, is estimated to be about 230 km/s, and the Milky Way is moving at some speed through the universe. Do these need to be these factored into redshift measurements?
 
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  • #2
iantresman said:
Presumably, measurements of the speed of light would show a redshift up to ±30km/s? Are redshift measurements this accurate?
It depends on the measurement. The best spectrometers are sensitive to about 1m/s for single stars, those are used to search exoplanets.
The orbit of earth, the rotation of Earth (still several hundred meters per second) and the influence of the moon (~10m/s) are well-known, so they are always taken into account where they are relevant.

iantresman said:
Likewise, the speed of the Solar System around the Milky Way, is estimated to be about 230 km/s, and the Milky Way is moving at some speed through the universe.
There is no "speed through the universe" as all motion is relative. We have some known velocity relative to the local cosmic microwave background, this is taken into account.
 

1. What is redshift and how does it relate to the speed of light?

Redshift is a phenomenon observed in light from distant objects that appear to be moving away from Earth. This is because the light waves from these objects are stretched, causing them to appear more red. The amount of redshift can be used to calculate the object's velocity, which is directly related to the speed of light.

2. How does Earth's orbital speed affect the measurement of redshift?

Earth's orbital speed does not directly affect the measurement of redshift. However, the relative motion of Earth and the object being observed can contribute to the overall redshift measurement. This is taken into account when calculating an accurate velocity for the object.

3. What is the significance of redshift in studying the universe?

Redshift is a valuable tool for studying the expansion of the universe. It allows us to measure the distances and velocities of distant objects, providing evidence for the theory of the Big Bang and the expansion of the universe. Redshift can also be used to study the distribution of matter and the overall structure of the universe.

4. Is the speed of light always constant, even in different reference frames?

Yes, the speed of light is a universal constant and is not affected by the reference frame it is measured in. This is one of the fundamental principles of Einstein's theory of relativity.

5. How do redshift and Earth's orbital speed support the theory of general relativity?

Redshift and Earth's orbital speed both play a role in the theory of general relativity. The observed redshift of light from distant objects can be explained by the curvature of spacetime, as predicted by general relativity. Earth's orbital speed also affects the measurement of time and space, as explained by the theory.

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