Cosmic Distances and Measurement
MS-ESS1-3

 

The universe is really quite a large place. In fact, it is so large that it really doesn't make sense to measure it using familiar units such as inches, feet, or even miles. The problem with measuring the universe in miles is that the numbers will be so large, that they just don't make sense to the average person.

In order to make distances in the universe more understandable, new units had to be chosen. Scientists decided to use the speed of light as a way of measuring the vast distances in the universe. We know that nothing is faster than the speed at which light is able to travel. By carefully calculating how far light can travel in a second, or a minute or even a year, we an use those values to measure distance.

The following values have been established for the speed of light.

• A beam of light travels 186,000 miles, or 300,000 kilometers in one second. This distance is referred to as one light-second.
• A beam of light travels 6,000,000,000,000 (6 trillion) miles, or 10,000,000,000,000 (10 trillion) kilometers in one year. This distance is called a light year.
• In other words, a beam of light will travel around the world about seven times in one second. That's about 12 million miles a minute! And that's the fastest speed there is! Nothing can move faster than light! (As far as we know!)

Using these values, we know that our sun is about 8 light minutes or (92,000,000 miles) away from the Earth. That means that it would take abeam of light coming from the sun a full eight minutes to reach the Earth.

We also know that the most distant objects that can be seen from Earth are about 15 billion (15,000,000,000) light years away! That means that a beam of light leaving these objects will take about 15 billion years to reach our wonderful world!

The famous scientist, Albert Einstein developed his Theory of Spacetime based on these facts. His theory states that "as you look into space, it's like you're looking back in time". He knew that because the universe is so large, it takes a while to get a message, (or a beam of light) from one place to another. By the time that the message gets to its destination, it will be "old news". If you look at our sun for example, which is only 8 light minutes away, the image that you see is already eight minutes old by the time it arrives here. When you look at the sun, you're not seeing it as it is RIGHT NOW, but you're looking at it as it appeared eight minutes ago. The sun probably isn't going to change much in only eight minutes, but it might. Things get stranger as you move further and further from Earth. Let's say that a star is one million light years from Earth. By the time a beam of light from that star reaches this wonderful planet, it's already a million years old. That star might not even exist today. When you look upon that star at night, you're looking at it as it looked a million years ago. This is what the theory of spacetime is all about. The stars that you see in the sky at night might not even be there today. When you look at the stars at night, you're literally looking into the past. It is also interesting to consider what a creature on a planet a million or more light years from Earth would see when he/she/it looks at the Earth. Would they see the Earth as it is today?