Define one parsec. Express it in terms of metres.

Explanation

To define one parsec and express it in terms of meters, we can follow these steps:

### Step 1: Understanding the Definition of a Parsec
A parsec (pc) is defined as the distance at which one astronomical unit (AU) subtends an angle of one arcsecond.

### Step 2: Define Astronomical Unit
1 AU is the average distance from the Earth to the Sun, which is approximately \(1.5 \times 10^{11}\) meters.

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