Last week, we have talked about **large numbers and one million**. In this post, we will talk about some of the practical uses of large numbers.

One of the uses of large numbers is to measure long distances; for instance, distance between celestial objects. Shown below is a table of the distances of the planets from the sun and from earth rounded off to the nearest thousand kilometers. Giving a speed of a commercial airline (approximately 500 kilometers per hour), a trip from Earth to Venus will require us 10 years of travel while traveling to Pluto will require us 1,306 years. Shocked?

**By the way, Pluto has recently been demoted. Recent updates made it clear that it does not qualify being one of the planets.*

**What is a light year?**

If we are going to measure the distances between the stars or between two planets, we will have difficult problem with large numbers. Proxima Centauri, for instance, the nearest star (except the sun of course) is about 39,700,000,000,000 kilometers. The distance of other stars will probably have more zeroes than we can imagine.

Due to this problem, scientists developed a unit which will be appropriate for measuring distances in space, one of them is *light year*. A light year is the distance that a light can travel in one year. A light can travel at approximately 300,000 km per second.

There are 31,104,000 seconds in one year, which makes one light year approximately equal to 9,331,200,000,000** km! This means that Proxima Centauri is about 4.25 light years away from the sun. If we are going to go to Proxima Centauri using our airplane above, we will arrive there at about 79.4 billion years. Note, however, scientists estimate that the earth is only about 4.6 billion years, the earth will probably be long gone after we reach Proxima Centauri.

In the next article, we will discuss why it is very difficult to model large distances and large objects.

**According to Wikipedia, it is exactly 9,460,730,472,580.8 km.

**Related Articles**

- Making Sense of Exponential Growth
- Large Numbers and One Million
- Counting the Infinite: A Glimpse at Infinite Sets