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A light year (ly) is a unit of measurement commonly used in astronomy to express distances between stars, galaxies, and other celestial objects. Despite its name, a light year is not a measure of time, but of distance—specifically, how far light travels in one Earth year.
Light travels at a speed of approximately 299,792 kilometers per second (km/s) in a vacuum.
In one year, this speed allows light to cover roughly 9.46 trillion kilometers (5.88 trillion miles).
Therefore, 1 light year = 9.46 trillion km.
Distances in space are immense, making conventional units like kilometers or miles impractical. For example:
Proxima Centauri, the nearest star to the Sun, is about 4.24 light years away.
The Andromeda Galaxy, our neighboring galaxy, is about 2.537 million light years away.
Using light years allows astronomers and students to understand and compare astronomical distances more easily.
1 light year = distance traveled by light in one year
Light travels ~300,000 km/s, covering vast cosmic distances quickly
Not a measure of time, energy, or mass
Because the term includes “year,” some may think it measures time, but it only indicates how far light travels in that time.
It is not related to energy (joules) or mass (kg).
Light year = unit of distance
Distance light travels in one year (~9.46 trillion km)
Used in astronomy for stars, galaxies, and cosmic measurements
Not a unit of time, mass, or energy
👉 Correct Answer: Option 3 – Distance
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