Definition

1. Noun:
   • Hubble's Law: In astronomy, the principle stating that the velocity at which a distant galaxy is receding from an observer is directly proportional to its distance from that observer. This observed relationship is a key piece of evidence for the expansion of the universe.

Usage

• The term "Hubble law" is used primarily in cosmological and astronomical contexts to describe the relationship between redshift and distance.
• It is often stated with the formula: v = H₀ × d, where is the recession velocity, is the proper distance, and is the Hubble constant.

Examples

• Noun:
  • The discovery of the Hubble law provided the first observational foundation for the Big Bang theory.
  • Astronomers use the Hubble law to estimate the distances to faraway galaxies by measuring their redshifts.

Advanced Usage

• "Hubble flow": The motion of galaxies resulting from the expansion of the universe, as described by the Hubble law.
  • Galaxies embedded in the Hubble flow are receding from each other.
• "Hubble constant (H₀)": The constant of proportionality in the Hubble law, representing the rate of expansion of the universe.
  • Precisely measuring the Hubble constant is a major goal of modern cosmology.

Variants and Related Words

• Hubble's law: The most common variant, often used interchangeably with "Hubble law."
• Hubble-Lemaître law: An alternative name acknowledging the contributions of astronomer Georges Lemaître.

Synonyms

• Law of redshift: A descriptive synonym emphasizing the observed phenomenon.
• Cosmic expansion law: A broader term referencing the underlying cause of the relationship.

Related Phrases

• To obey the Hubble law: Describes galaxies whose motion conforms to the predicted relationship.
  • Most galaxies on large scales obey the Hubble law.

Noun

1. (astronomy) the generalization that the speed of recession of distant galaxies (the red shift) is proportional to their distance from the observer