What is a light year?
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
). 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.
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.
