LIGHT YEAR – Why We Use Light Years

What is a light year?

A light year is a measure of distance, not time (as the name implies). A light-year is a distance traveled by a ray of light in one earth year or 6 trillion miles (9.7 trillion kilometers).

On the scale of the universe, distance is not to be measured in miles or kilometers. As you estimate the time it takes to drive to the grocery store (“the grocery store is 15 minutes away”), astronomers measure the distance the stars take as we travel. . For example, the star closest to our Sun, Proxima Centauri, is 4.2 light-years away.

How far is the light-year?

Unlike the speed of your car, when mistakes are made, the speed of light is constant throughout the universe and is considered very accurate. In a vacuum, light travels at a speed of 670,616,629 miles (1,079,252,849 kilometers per hour). The result: one light-year equals 5,878,625,370,000 miles (9.5 trillion kilometers). At first glance, this may seem like an extreme distance, but the vastness of the universe dwarfs this length.

Why Use Light Years?

Measuring miles or kilometers on an astronomical scale is extremely difficult and impractical. Starting from our cosmic neighborhood, the nearest star-forming region, the Orion Nebula, is 7,861,000,000,000,000 miles, or just 1,300 light-years away. Our nearest spiral galaxy, the Andromeda Galaxy, is 2.5 million light-years away. Some of the farthest galaxies we can see are billions of light-years.

Measuring in light-years allows astronomers to determine how far they are looking. As the light takes time to travel to our eyes, everything we see in the night sky has already happened. In other words, when you observe a few light-years away, you see it exactly as it appeared a year ago. We see that the Andromeda Galaxy appears 2.5 million years ago. The cosmic microwave background, the farthest object we can see, is our oldest view of the universe, dating back to 13.8 billion years after the Big Bang.

What are the alternatives for light years?

Astronomers also use parcels instead of light-years. In short for parallax seconds, a parsec comes from the use of a triangle to determine the distance of the stars. More specifically, the distance of a star that changes in the sky to 1 arc second (1 / 3,600 degrees) after the Earth orbits the Sun. One arc second equals 3.26 light-years.

Like degrees, a light-year can be divided into smaller units, such as hours, light minutes, or light seconds. For example, the Sun is more than 8 light minutes away from Earth, while the Moon is one light away from another. Scientists use these words when talking about communication with deep space satellites or rovers. Due to the limited speed of light, it can take more than 20 minutes to send a signal to the Curiosity Rover on Mars.

Whether it is light-years or parsecs, astronomers will continue to use both to measure distances in our vast and vast universe.

What is the history of the lighthouse?

When we use a powerful telescope to look at distant objects in space, we look back in real-time. How can this be?

Light travels at 186,000 miles per second. It seems really fast, but objects in space are so far away that their light takes so long to reach us. The farther we see an object, the farther we see it.

Our Sun is the star closest to us. It is about 93 million miles away. Therefore, it takes about 8.3 minutes for sunlight to reach us. This means that we always see the sun about 8.3 minutes earlier.

Our nearest star is about 4.3 light-years away. Therefore, when we look at this star today, we actually see it as it was 4.3 years ago. All other stars that we can see with our eyes are thousands of light-years away.

Stars are found in large clusters known as galaxies. A galaxy may contain millions or billions of stars. Therefore, we have seen Andromeda for the last 25 million years. The universe is full of billions of galaxies, and everything is far away. Some of these galaxies are distant.

In 2016, NASA’s Hubble Space Telescope spotted the far-sighted galaxy, the GN-z11. It was one of the first galaxies to form in the universe.

Learning about the first galaxies to form after the Big Bang, such as this, helps us understand what the early universe was like.

Why do astronomers measure distances in light years?

Familiar units such as kilometers and miles are absurd to describe the vastness of the universe. You could say that it is about 24,900,000,000,000 miles – or to save a lot of breath and call a distance of 4.24 light-years.

Most of the stars you see at night are within a few hundred light years of the Earth. The Milky Way, where we live, is 100,000 light years.

How do we know the speed of light?

Critical insights came from the seventeenth-century Danish astronomer Ole Roemer. In the 1660s, he was studying one of Jupiter’s moons, Io: when he noticed something strange: when Jupiter and Earth were at the greatest distance from each other, minutes after Io were predicted by astronomers The latter will fall into the shadow of Jupiter. When the two planets were closest to each other, it is likely that the event occurred a few minutes earlier.

The Romans felt that the delay had nothing to do with Io. Rather, it was an illusion due to the time it took for light to travel when the Earth and Jupiter were opposite to the Sun. Their calculations show that light travels at a speed of 131,000 miles per second – a very good figure, 60 years after the invention of the telescope.

Who coined the term light-year?

Frederick Ereko, an astronomer and scientific historian of the Paris Observatory, states: “The distance of the speed of light occurred at the end of the 17th century.

People quickly adapted to the idea, and it is impossible to accurately credit any one person. However, Arnu points to a good candidate: in 1694, the English scholar Francis Roberts remarked, “It takes us longer to travel light to the stars than we travel to western India.”

Initially, these ideas were unclear because scientists only had a rough idea of ​​how far away the stars were. The most significant moment came in 1838, when German astronomer Friedrich Bessel measured the distance from the 61 sine star. Describing the large numbers he had obtained, Bezell wrote, “Light takes 10.3 years to travel this distance.” It is the closest thing to a specific moment when a specific idea of ​​a light year is born.

Within a few decades, light years were common in popular science fiction. But professional astronomers have long opposed the use of the term – for a surprising reason. They scientifically inadequately calculated light years because they could not be directly measured.

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