What is a foot?
The foot is an imperial and US unit of length equal to 12 inches, or exactly 30.48 centimeters. It is a third of a yard and 1/5,280 of a mile.
The foot began as the length of a human foot, and so differed from place to place and from person to person. The modern international foot was fixed at exactly 0.3048 meters by agreement in 1959.
People's height is given in feet and inches in the US and UK, and aircraft altitude is given in feet nearly everywhere, metric countries included.
What is a lightyear?
A lightyear is a unit of measurement used in astronomy to describe vast distances in space. It represents the distance that light travels in one year, which is approximately 5.88 trillion miles or 9.46 trillion kilometers. The term "lightyear" is derived from the fact that light, which travels at a speed of about 186,282 miles per second (299,792 kilometers per second), can cover an incredible distance in the span of a year.
Light has a finite speed, so a galaxy a billion lightyears away is seen as it was a billion years ago. That is how astronomers look back at the early universe – the farther the galaxy, the older the picture.