What is a yard?
A yard is 3 feet or 36 inches. In the US you mostly see it on football fields, which run 100 yards between the goal lines, and in the UK short road distances are still signed in yards.
The yard is traditionally the distance from the nose of King Henry I of England to the thumb of his outstretched arm, though its length varied from place to place for centuries. It was only fixed internationally in 1959, at exactly 0.9144 meters.
Nearly every other country uses the meter instead. In the US, bulk soil and mulch are still sold by the cubic yard, which is 27 cubic feet.
What is a Parsec?
A parsec is a unit of length used in astronomy to measure vast distances between celestial objects. The term "parsec" is derived from the words "parallax" and "second," which refer to the method used to calculate this unit. Specifically, a parsec is defined as the distance at which an object would have a parallax angle of one arcsecond when observed from opposite ends of Earth's orbit around the Sun.
To understand the concept of a parsec, it is important to grasp the idea of parallax. Parallax is the apparent shift in the position of an object when viewed from different vantage points. In the case of astronomy, scientists use the Earth's orbit as a baseline to measure the parallax of distant stars. By observing a star from opposite ends of Earth's orbit, astronomers can calculate the angle of parallax and subsequently determine the star's distance.