# The light year is a measure of _____, not ______.

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The light year is a measure of _____, not ______.
1. Kilometers; Mile
2. Time; Distance
3. Distance; Time
4. Magnitude; Shape

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Correct Answer - Option 3 : Distance; Time
• Length is a measure of the size or distance between two points.
• The SI unit of length is the meter (m).

Light Year:

• A light-year is a unit of distance.
• A light-year is the distance a beam of light travels in a single Earth year, or 6 trillion miles (9.7 trillion kilometres).
• One light-year is the distance travelled by light in a vacuum in one year.
• A light-year is a convenient unit of measurement of large distances.
• Generally, a light-year is used to represent astronomical distances
• 1 light year = 9.46 × 1015 m.

Thus, the light-year is a measure of distance, not time.

Parsec (parallactic second):

• It is the largest practical unit of distance used in astronomy.
• It is defined as the distance at which an arc of the length of 1 astronomical unit subtends an angle of 1 second of arc.
• 1 parsec = 3.08 × 1016 m

Astronomical unit:

• It is defined as the mean distance of the earth from the sun.
• It is used in astronomy to measure the distance of planets.
• 1 astronomical unit = 1 AU = 1.496 × 1011 m