What physical quantity does the light-year (LY) measure, despite its naming convention?
Answer
Distance traveled by light in one Earth year through a vacuum
The light-year (LY) is a unit used to quantify cosmic separation, specifically measuring the linear distance that light traverses over the course of one full Earth year while traveling through a vacuum. Although the term contains 'year,' it explicitly quantifies distance, not time. Given the incredible speed of light—about 299,792,458 meters per second—a single light-year represents an enormous distance, approximating 9.46 trillion kilometers, making it necessary for describing interstellar gulfs where the Astronomical Unit becomes too small.
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