Definition

1. Noun:
   • A standard unit of measurement for distance in astronomy: The astronomical unit is a unit of length used to express distances within our solar system. It is defined as the average distance from the center of the Earth to the center of the Sun.

Usage

• The astronomical unit (abbreviated as AU or au) is primarily used to describe the distances between planets, asteroids, comets, and other objects orbiting the Sun. It provides a convenient scale for the solar system, making vast distances easier to comprehend and compare.

Examples

• Noun:
  • The average distance from the Sun to Mars is about 1.5 astronomical units.
  • Astronomers often measure the semi-major axis of an orbit in astronomical units.
  • One astronomical unit is roughly 150 million kilometers.

Advanced Usage

• "in astronomical units": Used to specify that a given distance is measured using this unit.
  • The dwarf planet Pluto orbits at an average distance of about 39.5 in astronomical units.

Variants and Related Words

• AU / au (abbreviation): The standard abbreviation for "astronomical unit."
  • Jupiter is 5.2 AU from the Sun.
• Light-year (n): A different, much larger unit of astronomical distance, representing the distance light travels in one year. It is used for interstellar distances, not within the solar system.
• Parsec (n): Another unit of distance used in astronomy, equal to about 3.26 light-years, commonly used for interstellar and galactic scales.

Synonyms

• AU: The standard abbreviation serves as a direct synonym in scientific contexts.
• Mean Earth-Sun distance: A descriptive synonym that defines the unit.

Related Phrases

• "measured in AU": Indicating the use of this specific unit for a measurement.
  • The comet's aphelion was measured in AU.

Noun

1. a unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)