Define par sec and light year. How are they related?

Explanation

### Step-by-Step Solution:

1. **Definition of Parsec**:
- A parsec is a unit of length used in astronomy to measure large distances to astronomical objects outside the Solar System.
- It is defined as the distance at which one astronomical unit (the average distance from the Earth to the Sun) subtends an angle of one arcsecond.
- In simpler terms, if you have a triangle where one side is the distance from the Earth to the Sun (about 1 AU), and the angle at the Earth is 1 arcsecond, then the distance to the star at the apex of the triangle is one parsec.

2. **Definition of Light Year**:
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