Light Spead and Measuring the Size of the Universe


Light is fast, but the universe is gigantic. Even light takes time to travel from one place to another. It travels 300,000 kilometers per second. Light from the Sun takes as long as eight minutes and twenty seconds to reach Earth. Far as the Sun is, 150 million kilometers away from Earth, it is the nearest star.

One of the earliest attempts to measure the speed of light was Galileo’s. He and his assistant held lanterns at a distance, a mile apart, then Galileo would flash his lantern and whenever the assistant sees light, he would flash his lantern as well; then Galileo would record the time light takes to travel. Galileo, unfortunately, was not successful in calculating the speed of light.

In 1670, Danish astronomer, Ole Roemer, was observing Io, Jupiter’s closest moon, and the time it takes to make a complete orbit around Jupiter. He noticed that it takes 1.76 days. Logically, the distance does not change, so Roemer thought that he would be able to predict Io’s motion accurately. However, Roemer noticed that the moon does not appear where he expects. He realized that he sees Io sooner when the Earth is closer to Jupiter. It all depends on light; Roemer did not see Io as it is, he saw Io as it was. From the varied observations of Io and the distance between Jupiter and Earth, Roemer calculated the speed of light.

It is quite challenging to calculate distances in this large universe, so scientists came up with a way of measurement, which is the light year. It is the distance light takes in one year. Light travels 300,000 kilometers per second, so a light year is 9,500 billion kilometers. When we say that the Andromeda Galaxy is 2.3 million light years away, you get a picture of how the universe is really large.

The Parsec is another measuring unit. It equals 3.26 light years. Scientists use it to measure distances beyond our solar system.

Light travels fast; it takes light 1.3 seconds to travel from Moon to Earth, 5 hours and 40 minutes to travel from the Sun to Pluto, and almost 100,000 years to cross our galaxy. If theoretically speaking, human beings travel by the speed of light, they will take 100,000 years to cross the galaxy, if they live that long.

We take the knowledge we have of the speed of light for granted. It is a fact that light coming from the Sun takes 8 minutes and 20 seconds to reach Earth. In the past, it took observation and hard work. Calculating the speed of light was not easy. It included attempts of scientists such as Galileo and Roemer. If it weren’t for them, we would not have known how fast light travels, and concluded how huge the universe is. Thanks to scientists, the beam of knowledge shines brightly.


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