# What is a light year?

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What is a light year?

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Its name implies it has to do with time, but it is actually a measure of distance. Because objects beyond the solar system are so immensely far away, ‘miles’ becomes too small a unit. It becomes necessary to use a larger scale.

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The concept of a light year can be rather confusing at first. A year is a unit of time, but a light year represents a unit of distance. Specifically, it is the distance that light travels in one year. Since light travels at 3 108 m/s and a year consists of 31.536 106 seconds, a light year is therefore equivalent to 9.46 1015 meters.

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). The events of the early universe radiated heat and light. That heat and light has been traveling through space for about 14 billion years, give or take. When we gather light from the deepest parts of the universe, as the Hubble Space Telescope has done, we see light from when light first emerged from this early time in the universe. That’s as far as we can see and that is the limit to what we refer to as the visible universe. But it is widely thought that the ‘real’ universe extends far beyond the visible limit because the light from those more distant parts hasn’t had time to get to us, yet. The second portion of the answer has to do with what makes up the parts of the universe.

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The light-year is probably the most misused scientific term in the popular literature. If you watch old science-fiction films carefully, you may hear the characters using the light-year as a unit of time – which it is not! The light-year is actually a unit of distance commonly used in astronomy. Astronomy is the scientific study of the universe beyond the Earth: planets, stars, galaxies and solar systems. Because of the size of these objects and the distances between them, measurements and calculations often require working with very large numbers. Specialized units – such as the light-year – make these calculations much less cumbersome. A light-year is defined as the distance light travels during one year. Light from the sun travels with a speed of about 300,000,000 meters per second. By multiplying the speed of light by the number of seconds in one year, we find that one light-year is equal to 9.5 x 1015 (that’s 9,5000,000,000,000,000!) meters. To give you an idea of how large a dist

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A light year is the distance that light travels in one year through vacuum or empty space. Light moves though vacuum at just over 186,282 miles (299,792 km) per second, reaching an astounding 5.8 trillion miles (9.4 trillion km) in one year. With such great distances, relative terms like “miles” and “kilometers” become inefficient and meaningless. Instead, astronomers speak in terms of light years to describe great distances. Before we can appreciate speaking of distances in terms of light years, it helps to grasp how far a single light year spans. In terms of our own solar system, defined for this exercise by the orbit of the former planet Pluto, the solar system would have to be 800 times larger to be a single light year across. Put another way, the sun is about 93 million miles from earth, and one would have to log 31,620 round trips from the earth to the sun to travel the distance of a light year. In addition to the light year, scientists also speak in terms of light seconds and li