Definition

1. Noun:
   • A specific astronomical time period: A "sidereal month" is the precise time it takes for the Moon to complete one full orbit around the Earth, measured relative to the fixed background of distant stars. Its duration is approximately 27.322 days.

Usage

• The term "sidereal month" is used in astronomy and celestial mechanics to describe the Moon's orbital period from a fixed stellar reference point. It is distinct from other lunar months, such as the synodic month (the cycle of lunar phases).

Examples

• Noun:
  • A sidereal month is about 2.2 days shorter than the more familiar synodic month.
  • Astronomers calculated the satellite's orbit based on the length of the sidereal month.

Advanced Usage

• In comparative astronomy: The concept of a sidereal month is fundamental for understanding the Moon's motion in an inertial frame of reference, separate from its phases as seen from Earth.
  • The difference between the sidereal and synodic months explains why we don't have a solar eclipse every new moon.

Variants and Related Words

• Sidereal (adj): Of, relating to, or measured with respect to the distant stars (apparent as fixed points in the sky).
  • Sidereal time is based on the Earth's rotation relative to the stars, not the Sun.
• Synodic month (n): The period between successive new moons (e.g., from full moon to full moon), approximately 29.53 days. This is a related but distinct concept.

Synonyms

• Lunar sidereal period: A more descriptive synonym for "sidereal month."

Notes on Meaning

• The "sidereal month" refers specifically to an orbital period relative to fixed stars. It is a precise scientific term and is not used in everyday contexts to describe calendar months or lunar phases visible from Earth.

Noun

1. period between successive conjunctions with a star, 27.322 days