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About these units
Yard (yd)
A yard equals 3 feet or 36 inches and serves as a mid-range imperial length unit. Historically, one definition of the yard was the distance from the tip of King Henry I's nose to his thumb when his arm was extended, though later attempts standardized the measure. Today, yards appear in sports (football, golf), textiles (fabric sales), and landscaping. In construction and engineering, the yard is sometimes used for larger distances where a foot would be too small a unit and a mile too large. Because it divides cleanly into both inches and feet, the yard plays a structural role in the imperial measurement system. It bridges the gap between human-scale and large-scale distances.
Light Year (ly)
A light year is the distance that light travels in a vacuum in one Julian year, equal to approximately 9.4607 × 10¹⁵ meters. Despite its name, it is a unit of distance, not time. The light year arose from the need to express vast astronomical separations using a concept familiar to laypeople: the finite speed of light. By linking distance to time, it becomes easier to comprehend that observing distant stars is also an act of looking back in time. The light year is especially useful when describing the locations of nearby stars, nebulae, and star-forming regions. For example, Proxima Centauri lies roughly 4.24 light years away. Because light moves at about 300,000 km/s, even the nearest galactic objects are many trillions of kilometers distant, making ordinary units impractical. One of the light year's greatest strengths is how vividly it illustrates the immensity of space. When astronomers say a galaxy is millions of light years away, they convey not only a vast spatial separation but also the staggering temporal depth of the universe. The light year therefore plays a dual role as both a scientific measurement and an educational tool that grounds cosmic distances in a memorable framework.