Hubble constant

Definition

The Hubble constant is the rate of expansion of the universe, measured in kilometers per second per megaparsec (km/s/Mpc). It provides a relationship between the distance of galaxies and their recessional velocity due to cosmic expansion.

5 Must Know Facts For Your Next Test

1. Edwin Hubble first determined the value of the Hubble constant in 1929 by observing the redshift of distant galaxies.
2. The precise value of the Hubble constant is still under debate, with estimates ranging from about 67 to 74 km/s/Mpc.
3. The Hubble constant helps astronomers estimate the age of the universe, which is approximately 13.8 billion years old.
4. Observations from different methods, such as Cosmic Microwave Background (CMB) measurements and local distance ladder techniques, can yield different values for the Hubble constant.
5. A higher value of the Hubble constant implies a younger universe, while a lower value suggests an older universe.

Review Questions

• What does the Hubble constant measure?
• Why is there a discrepancy in the measured values of the Hubble constant?
• How does the Hubble constant help determine the age of the universe?

Related terms

Redshift:

A shift toward longer wavelengths in light from distant galaxies indicating they are moving away.

Cosmic Microwave Background (CMB): Radiation leftover from an early stage in the development of the universe, providing evidence for its origins.

Distance Ladder: A set of methods by which astronomers determine distances to celestial objects.