Light-Year

Light-Year

A light-year is a unit of distance used in astronomy. It is the distance that light travels in one Julian year (365.25 days).

Definition

The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications. The unit most commonly used in professional astrophysics is the parsec, which is equivalent to approximately 3.26 light-years.

Calculation

Light travels at a speed of about 299,792 kilometers per second (186,282 miles per second). Therefore, a light-year is equal to 9.461 × 10^12 kilometers (5.879 trillion miles) or 63,241 astronomical units.

Usage

The light-year is often used in popular science books and articles because non-specialists are more familiar with the concept of "year" than with the parsec or astronomical unit.

See also

• Parsec
• Astronomical unit
• Speed of light
• Julian year

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