# How do astronomers define a light year?

A astronomical unit of distance

A light year is the distance traveled by light in one (1) light year, according to the definition of the astronomical unit of distance.

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The problem with the definition of light year (ly) is the duration of year. IAU year is Julian 365.25 days of 86400 s/day. An improved ly is for Gregorian 365.2425 days

The approximate value of a light second (ls) is 299792458 meters. A sidereal year is the length of time light travels.

The sidereal year is approximated as follows: 365.25 days for the older approximation, 365.2425 days for the later approximation, and 365.256363 days for the more significant digits (sd).

In any case, using the standard (tallying) 5-sd approximation of 1 ly = 1.0950 E+11 meters is safe.

It is preferable to express the year in days and define day = 86400 s.

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A light year is defined as the distance that light travels in one year in a vacuum. It is approximately 9.461 trillion kilometers or 5.879 trillion miles.

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When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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