What observations were used by Edwin Hubble to show that the universe is expanding?
- The distance to a galaxy is proportional to its luminosity.
- The distance to a galaxy is inversely proportional to its apparent size.
- The distance to a galaxy is proportional to its velocity relative to the Milky Way.
- The distance to a galaxy is proportional to its rotational velocity.
The distance to a galaxy is proportional to its velocity relative to the Milky Way.
The fact that the distance to a galaxy is proportional to its velocity relative to the Milky Way indicated to Hubble that the universe is expanding.
The correct observation used by Edwin Hubble to show that the universe is expanding is:
- The distance to a galaxy is proportional to its velocity relative to the Milky Way.
To understand how Hubble came to this conclusion, we need to look at Hubble's Law and how it relates to the expansion of the universe. Hubble's Law states that the recessional velocity of a galaxy is directly proportional to its distance from us. In simpler terms, the farther away a galaxy is, the faster it moves away from us.
To measure the velocities of galaxies, Hubble used a technique called redshift. When light from a distant object moves away from us, it gets stretched, causing a shift towards the red end of the electromagnetic spectrum. By measuring the amount of redshift in the light from galaxies, Hubble could determine their velocities.
Hubble then compared these velocities with the distances to the galaxies measured by Cepheid variable stars (stars with a regular pulsation period related to their brightness). He found a clear linear relationship where the recessional velocity increased as the distance to the galaxy increased. This confirmed the expansion of the universe, implying that all galaxies are moving away from each other.
Therefore, the observation used by Edwin Hubble to show that the universe is expanding is that the distance to a galaxy is proportional to its velocity relative to the Milky Way.