What is a light year

(ORDO NEWS) — A light year is a measurement of distance, not time (as the name might suggest). A light year is the distance a beam of light travels in one Earth year, or 9.7 trillion kilometers (6 trillion miles).

On the scale of the universe, measuring distances in kilometers or miles does not reduce this distance. In the same way that you can measure the distance to a grocery store in the time it takes to get there by car (for example, the store is 15 minutes away), astronomers measure the distance to the stars in the time it takes for light to reach us. . For example, the closest star to our Sun, Proxima Centauri, is 4.2 light years away.

How far is a light year?

Unlike the speed of your car, the speed of light is constant throughout the universe and is known with great precision. In a vacuum, light travels at a speed of 1,079,252,849 km/h.

To find the distance of a light year, you multiply this speed by the number of hours in a year (8,766). Result: one light year is equal to 9.5 trillion km. At first glance, this may seem like an incredible distance, but the vast scale of the universe reduces this length.

Why use light years?

Measuring in kilometers or miles on an astronomical scale would be extremely cumbersome and impractical. Starting from our cosmic neighborhood, the nearest star-forming region to us, the Orion Nebula, is at a distance of 12,650,000,000,000,000 km, or, more simply, 1300 light-years.

The center of our galaxy is about 27,000 light years away. The nearest spiral galaxy to us is Andromeda, located at a distance of 2.5 million light years. Some of the most distant galaxies we can see are billions of light years away.

The measurement in light years also allows astronomers to determine how far back in time we are looking. Because it takes time for light to reach our eyes, everything we see in the night sky has already happened. In other words, when you observe something at a distance of 1 light year, you see it exactly as it appeared exactly one year ago.

We see the Andromeda galaxy as it was 2.5 million years ago. The most distant object we can see, the cosmic microwave background, is also our oldest view of the universe, having emerged just after the Big Bang about 13.8 billion years ago.

Alternatives to light years

Astronomers also use the parsec as an alternative to the light year – short for PARallax and SEC. To be more precise, this is the distance to a star whose apparent position shifts 1 arc second (1/3600 of a degree) in the sky after the Earth has completed a half-way trip around the Sun. One arc second is equal to 3.26 light years.

Like degrees, a light year can also be broken down into smaller units – light hours, light minutes, or light seconds. For example, the Sun is over 8 light minutes away from the Earth, while the Moon is just over a light second away.

Scientists use these terms when they talk about communication with spacecraft or rovers. Due to the finite speed of light, sending a signal to the Curiosity rover to Mars can take more than 20 minutes.

Whether light years or parsecs, astronomers will continue to use them to measure distances in our vast and large universe.

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