Why do astronomers use units like light years instead of miles?

Answer 1

Light years are more convenient when measuring the enormous distances of space. One light year is 5,869,713,600,000 miles so it is much easier to use light years, especially when many objects in space are hundreds, thousands and millions of light years from Earth.

Answer 2

Let's take an example:-

Our nearest star - Alpha Centauri is:-

* Light years 4.37 * Parsecs 1.34 * Kilometers 4.13 x 1013 * Meters 4.13 x 1016

Betelgeuse is :-

* Light years 640 * Parsecs 197 * Kilometers 6 x 1015 * Meters 6 x 1018 IOK-1 (The furthest Galaxy Known)

* Light years 12.9 billion

* Parsecs 4 x 109 * Kilometers 1.22 x 1023 * Meters 1.22 x 1026

Which one is easier to remember?

Answer 3

There are two main reasons he light year is more convenient than miles.

Firstly space is very big. If we were to measure everything in miles it would become harder to comprehend for the layman to comprehend the difference in distances.

Let me give you an example. Take 3 stars & a galaxy:- the Sun, Proxima Centauri, Betelgeuse & the Andromeda galaxy.

The Sun is 92955887.6 miles away. This is OK but when we look at Proxima it is 24635923200000 miles away, Betelgeuse is 3754045440000000 miles away & Andromeda is 14664240000000000000 miles away. To most people these are just meaningless numbers.

Even if you use scientific notation the Sun is 9.9256*107 miles, Proxima 2.4636*1013, Betelgeuse 3.7540*1015 & Andromeda is 1.4662*1019 it is still pretty much incomprehensible to anyone that is not a mathematician.

If you use light time to display the distances, the Sun is 8 light minutes, Proxima is 4.2 light years, Betelgeuse is 690 light years and Andromeda 2.5 million light years it becomes obvious to everyone relative distances.

Another reason why using the light year is so we can tell when long ago the light left the star. For the Sun we see it as it was 8 minutes ago. If is was suddenly to stop shining we would no nothing until 8 minutes later. We see Proxima as it was 4.2 years ago, Betelgeuse 690 years ago and Andromeda 2.5 million years ago.

Answer 4

A light year is equal to approximately seven trillion miles. Our own galaxy, the Milky Way, is 200,000 light years in length on its major axis (80,000 light years on the minor axis) so there are lots of stars which are tens of thousands of light years away from us. Expressed in miles they would be on the order of hundreds of quadrillion miles away, and that is just an awkwardly large number.

Answer 5

Since one light year is about 5879 billion miles, the number of miles involved becomes cumbersome when you are dealing with extreme astronomical distances; for example some of the latest galaxies viewed by the Hubble telescope are 13 billion light years away. It's just a better unit of measurement for larger distances.

Answer 6

It's the same reason it's easier to use kilometers instead of inches, for measuring certain distances. The longer the distance is, the greater the need for a meaningful unit. For example the nearest galaxy to us is the Andromeda Galaxy, at 2,500,000 Light Years. One Light Year is 10,000,000,000,000 kilometres, meaning it is 25,000,000,000,000,000,000 kilometres away. Clearly kilometres are not a suitable unit for expressing such distances.

Answer 7

These Units are more related to the scale of Astronomy and gives smaller numbers to manipulate.

One AU is 93 million miles. Astronomical distances are thousands, or hundreds of thousands, of AUs - gazzillions of miles are less easy to manipulate!

Answer 8

The kilometer is a perfectly acceptable unit with which to describe the sizes of galaxies

and the distances between stars. It's just that if you use the kilometer, then the numbers

you have to handle are roughly ten trillion times bigger than they would be if you used the

light year instead, which quickly becomes quite inconvenient.

Answer 9

Meters, and even kilometers are so tiny they are virtually nonexistent compared to the vast distances involved in astronomical observations. Light years are at least at a scale where some galactic distances can be easily manipulated and to a degree grasped. It is a matter of suitability and proportion. We wouldn't measure our height in units consisting of one millionth the width of an electron.

Answer 10

It is more useful for expressing the distance to stars because one light year is 9.461 x 1015 meters so it helps astronomers to avoid having to use very large numbers. Even so they still have to use very large numbers.

A preferred unit is the Parsec, which is the distance to a star that has a parallax of one second of arc. That means its apparent position in the sky changes by one second of arc when viewed from either end of a baseline of one astronomical unit, which is 149.6 million kilometres. A parsec is 3.085 x 1016 meters, or 3.26 light years.