How are light-years measured?

Jacob

Jacob

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I am interested to know the answer to this question.

It seems to me that something that is for example a light-year away, if that could be measured, would only appear to us as it did a year ago and not as it is now. If we cannot observe it as it is now, how do we know how far away it is?
 
john w

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In the # of tribbles there are, lined up, from earth, to the Klingon quadrant?
 
The Barbarian

The Barbarian

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If it's a star, we can know which direction it's moving and how fast, by the spectrum shift. Knowing the distance, we can then infer where it actually is.
 
Jacob

Jacob

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john w said:
In the # of tribbles there are, lined up, from earth, to the Klingon quadrant?
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I have no idea about what you are asking john w. I feel my question falls in the area or scientific disciplines of Physics or Astronomy.
 
Jacob

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The Barbarian said:
If it's a star, we can know which direction it's moving and how fast, by the spectrum shift. Knowing the distance, we can then infer where it actually is.
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Can you explain this?

I believe you are saying you would start with a star, but I am asking about light-years for light meaning distant astronomical objects.
 
john w

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Untellectual said:
I have no idea about what you are asking john w. I feel my question falls in the area or scientific disciplines of Physics or Astronomy.
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Do you think, that Dr. Leonard McCoy, "Bones," should have gone down to those planets? He's a doctor, darn it, so why would he need to leave the Enterprise?
 
Jacob

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john w said:
Fair enough. How come, on TV, movies, they have sound(effects), in space? There is no air in space. No air-no sound. Inquiring minds want to know.
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Do I appear to be a teacher because of my question in the OP?

I don't have a TV either.

I have heard of Star Trek but I know next to nothing about it.
 
john w

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Untellectual said:
Do I appear to be a teacher because of my question in the OP?

I don't have a TV either.

I have heard of Star Trek but I know next to nothing about it.
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No TV? You mean you never saw the TV show, "Lost in Space?" I dug that Judy chick. The "Robot" got on my nerves, however.
 
Jacob

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john w said:
No TV? You mean you never saw the TV show, "Lost in Space?" I dug that Judy chick. The "Robot" got on my nerves, however.
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I don't know about these.

In Star Trek was there a Captain Kirk? I don't know that I would be able to recognize which one he is.
 
TulipBee

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Maybe the changes in color in file or devices determines distance. I've read something about red shift in film
 
gcthomas

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Untellectual said:
I am interested to know the answer to this question.

It seems to me that something that is for example a light-year away, if that could be measured, would only appear to us as it did a year ago and not as it is now. If we cannot observe it as it is now, how do we know how far away it is?
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That is a good question.

The distance in light years is defined as the product of the speed of light and the time the light has taken to arrive, which effectively means how far was it away when the light was emitted. (Specifically: the light-travel distance)

The distance that object is now is called the proper distance, and has to be calculated to allow for the motion in the intervening time. It can't be directly measured.

More info here: http://en.wikipedia.org/wiki/Distance_measures_(cosmology)
 
OCTOBER23

OCTOBER23

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UNTELECTUAL

TYPE GOOGLE SEARCH ON YOUR COMPUTER

AND THEN YOU TYPE - ASTRONOMICAL UNIT AU

AND NEXT YOU TYPE - STAR TREK YOUTUBE

AND NEXT YOU TYPE - BBC WORLD NEWS
 
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The Barbarian

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I checked with an astronomer I know, Riley Sinder, and he writes:

The unit usually used in professional astrometry is the distance that light travels in vacuum in one Julian year. Because it includes the word year, the term light-year is most often used when expressing distances to stars and other distances on a light year.

Astronomers do the same thing when figuring out the distance at which one astronomical unit subtends an angle of one second of arc. A 1987 monograph by Australian creationist Barry Setterfield had stimulated me to examine this problem.

If we cannot observe it as it is now, how do we know how long a foot or a meter is -- you are comfortable with these units because you use them every day. "Light year" is just a unit called a light switch – there it is! We don’t have to wait for the room to light up.

You are used to measuring distances in either inches/feet/miles or centimeters/meters/kilometers, depending on where you live.

We don't directly measure distances to anything light years away by timing light.

"Light year" is just thousands of years old, and yet we can see stars that are billions of light-years away. The distances are gigantic.

I thought he might be able to explain it in a way you could understand. (WFTH-I)
 
OCTOBER23

OCTOBER23

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Light travels at 186,000 miles per second.

Lightng travels at half that which is 93,000 miles per second.

Angels travel at the speed of lightning.

Eze 1:14 And the living creatures ran and returned as the appearance of a flash of lightning.

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Eze 1:13 As for the likeness of the living creatures, their appearance was like burning coals of fire, and like the appearance of lamps: it went up and down among the living creatures; and the fire was bright, and out of the fire went forth lightning.
Da 10:6 His body also was like the beryl, and his face as the appearance of lightning, and his eyes as lamps of fire, and his arms and his feet like in colour to polished brass, and the voice of his words like the voice of a multitude.
Mt 28:3 His countenance was like lightning, and his raiment white as snow:
 
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