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SteveAstronomers use units like light years because distances in space are incredibly vast, making miles impractical to use. A light year represents the distance light travels in one year, which is approximately 6 trillion miles. This unit allows astronomers to more easily conceptualize and compare vast distances in the universe.
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?
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.
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.
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.
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.
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.
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.
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Why are light years used to measure astronomical distance?
Light years are used to measure astronomical distances because the vastness of space makes conventional units impractical. A light year is the distance light travels in one year and provides a convenient way to express the immense distances between celestial objects. It allows astronomers to describe distances in terms of time taken for light to travel, rather than using large numbers with conventional units like kilometers or miles.
Is the apparent movement of a star used to measure its distance from Earth?
One common distance standard is the AU - Astronomic Unit which is about 150 000 000 km the average radius of the Earths orbit around the Sun. 1 AU is equal to exactly 149,597,870,700 metres (92,955,807.273 mi)
Why are astronomical units AU not use for measuring distances between celestial objects that lie outside the solar system?
Astronomical units (AU) are based on the average distance between the Earth and the Sun, which is about 93 million miles. This unit is not practical for measuring distances beyond our solar system due to the vast scales involved. For interstellar or intergalactic distances, astronomers use light-years or parsecs, which are much larger units that can accurately represent these immense distances. Additionally, the use of AU outside the solar system would lead to confusion and lack of precision in measurements.
Why do astronomers use light years insted of kilometers to mesure distances of stars?
Any length or distance can be expressed in any unit of length, but some units may result in inconveniently large or small numbers. When you talk about distances between stars, light years produce numbers that are much more convenient than kilometers would produce, just as it's a lot more convenient to talk about your drive to work in miles instead of inches. The nearest star outside of the solar system is roughly 4.3 light years away. That's a lot easier to read, say, and remember, than 40,680,000,000,000 kilometers.
Why should si units be used instead of other units?
There are different units for measuring different attributes.
