What is a light-year and how is it used?Answer:
A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.
Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.
In our solar system, we tend to describe distances in terms of the Astronomical Unit (AU). The AU is defined as the average distance between the Earth and the Sun. It is approximately 150 million km (93 million miles). Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.
For distances to other parts of the Milky Way Galaxy (or even further), astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3 light-years. Using the light-year, we can say that :
The Crab supernova remnant is about 4,000 light-years away.
The Milky Way Galaxy is about 150,000 light-years across.
The Andromeda Galaxy is 2.3 million light-years away.
Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.
In our solar system, we tend to describe distances in terms of the Astronomical Unit (AU). The AU is defined as the average distance between the Earth and the Sun. It is approximately 150 million km (93 million miles). Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.
For distances to other parts of the Milky Way Galaxy (or even further), astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3 light-years. Using the light-year, we can say that :
The Crab supernova remnant is about 4,000 light-years away.
The Milky Way Galaxy is about 150,000 light-years across.
The Andromeda Galaxy is 2.3 million light-years away.
It doesn't measure time, in other words it is incorrect to say the universe began 4.5 billion years ago with a bang just because you can see that far with a telescope. It's just a unit of measurement on a large scale. God is not limited by time. He could cross that distance in a millisecond. Man comprehension is limited and scientist understands very little about the universe, although they would have you believe different.
7 comments:
What a ridiculous claim to make. I was very pleased with this post until you started talking about God and how you cannot claim that the universe started 4.5 billion years ago by measuring lightyears (the current estimate is actually about 13.7 billion years ago anyway). You can. By looking at the rate at which things in the universe (stars, galaxies, floating debris etc.) are moving away from eachother, we can come to the conclussion that at some point, they must have all occupied the same space, approximately 13.7 billion years ago. If we looked 13.7 billion lightyears away with a telescope (which we can't anyway) we would see the birth of our universe, because the time it takes for the light to reach us from that point is 13.7 billion years - we would effectively be seeing ancient light which showed images of creation. Maybe God did create the universe, but considering how far our species has come, I think it is ridiculous to claim that "scientists understand very little about the universe, although they would have you believe different" and "it is incorrect to say the universe began 4.5 billion years ago with a bang just because you can see that far with a telescope". As a scientist myself, I can tell you that no scientist has ever said that they know everything about the universe, and most would happily say they know hardly anything about the universe, because it proves what an exciting and interesting place it is. Science isn't a conspiracy, science is the search for the truth. To say such a thing just proves your ignorance.
If everything in the universe is moving away from each other, where was the center? Something must be moving toward each other, somewhere? Also, maybe we can see only so far, but there may be more of the same farther out, but they might be out of our sight capabilities.I don't know, I'm not a scientist. On some issues I post more than one explanation. I report, you decide. But, scientist have only scratch the surface of knowledge about the universe, so it's too early to say 'for a fact'. Not all science searches for the truth. One person might be ignorant, another might be blinded to the truth. For those who do not believe in a creator, God said that he would cause them to reject the truth and believe a lie.
Oh, by the way, Thank you. I really do appreciate people that take the time to post a comment.
With time you need an oscillating (regular) base before you can frame the changing universe with a 'time system'. To use light years as a term of distance and then 'change' this to an expression of duration (unfolding time) is deeply erroneous.
If we took a more identifiable human measure, like 60mph in a car, then the Universe becomes 1.123 billion billion billion years old.
In an identifiable space (earth) we can understand our planet as 4.5 billion years old, but that is a different measure to the 13.7 billion years old we usually state of the Universe which again is a measure of distance, not of duration. Distance and duration are two different dimensions.
It's about time we realised that.
Anonymous, You lost me. Could you simplify your comment. Did you read my reply to Joel's comment?
An interesting discussion is definitely worth comment. There's no doubt that that you ought to publish more about this topic, it might not be a taboo subject but usually people do not discuss these subjects. To the next! Best wishes!!
Here is my web-site : old holborn
Post a Comment