The definition for the prime meridian is: The prime meridian with 0 degrees longitude runs through Greenwich. Polaris is the north star <span>at 50 degrees above the horizon, which means 50 degrees latitude.
</span>If you observe Polaris at 50 degrees of altitude, you are at latitude 50 North. You that's why you know that your boat's location is <span>50º north latitude and 0º longitude.</span>
