How are light-years measured?

[CabinetMaker]

Yes. Have you?

Oh yes. That is how I can so easily defeat your arguments.

:yawn: The evolutionists' cry of defeat.

Not a cry of defeat, just a simple challenge for you to support your assertions. You made a claim, it is your responsibility to provide experimental evidence to support it.

Your "answer" requires that we first assume the truth of what you are trying to prove.

Remember those articles you claim to have read, the speed of light has already been proven. You have asserted that it is not but, to date, have utterly failed to support.

 

[Ha Nazir]

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?

I hope you're not laboring under the delusion that man can actually measure the distance to distant stars. We can only estimate the distance based on physical observations here on earth.

The distance to the moon is a good example to understand this because we have been there and have placed instruments there to help us measure the actual distance. The distance to the moon varies during the course of it's orbit by a distance of 42,592 km (26,465 mi). When we speak of the distance to a body in space we are talking about an "average" distance and that is still just an estimation.

http://en.wikipedia.org/wiki/Lunar_distance_(astronomy)

 

[Jacob]

the speed of light is what I think is the speed of reality...FPS if you will..

Its how far light travels in a year, as previously posted.

So if we send out radio waves from the earth to space, a hundred years ago, then it is a 100 light years away...

The Einstein thought experiment was about what it would be like to travel at the speed of light, kinda like the match lit on the train thought experiment.I imagine as the light moves the physical universe seems to stand still, its all perspective really, and as we are told by Einstein, reality is nothing but a mere illusion,albeit a persistent one.

Here we know how long ago, whether we could do that then or not, the waves (albeit radio) were sent out. It is different to receive light from a distant star or galaxy.

 

[Jacob]

This statement is wrong. The speed of light is not affected by gravity. Large gravitational body act a gravity lens and will change the direction of the light. The speed of light does change based on the medium through which the light travels.

How do you know this?

The speed of the different wavelengths of light are equally changed.

So how does a prism work? The triangular shape is the key. Ax the light strikes the prism refract the different wavelengths at a different angle.

Please don't pay attention to Stripes notions regarding the speed of light. He casually disregards hundreds of years of research and testing and glibly replaces it with a self serving definition that completely fails to explain what is actually observed about the properties of light.

 

[Jacob]

By definition, a velocity is a magnitude (speed) and a direction. An escape velocity is the speed and direction that must be achieved to overcome the gravitational pull of a gravitational field.

Okay.

An orbital path is described by the velocity on the planet (speed and direction) as well as the gravitation of the star attempting to pull the planet in. The velocity of the star sets up a force, centripetal force, that opposes the the stars gravitational force resulting in the orbit of the planet. This is grossly over simplified as orbital mechanics is quite complex, but it is functionally what is going on.

Would you say an orbital path could also be a moon around a planet or a satellite?

 

[Jacob]

Light is hard to explain. It exhibits the properties of both a particle and a wave yet is not quite either one at the same time. We describe it using photons.

A "wave" caused by a physical disturbance or the motion of the tides would be different. Can you explain a particle and a wave in reference to light?

 

[Jacob]

The experimental setup Resurrected posted all those years ago shows your thinking to be wrong.

You are talking about an experiment that can be conducted on earth, and that light is indeed received.

I'm talking about a distance astronomical object, like a star outside of our solar system for example.

I don't know that we would be able to send light to the moon and measure when we receive indication that the light has made it there and back?

 

[Jacob]

I hope you're not laboring under the delusion that man can actually measure the distance to distant stars. We can only estimate the distance based on physical observations here on earth.

The distance to the moon is a good example to understand this because we have been there and have placed instruments there to help us measure the actual distance. The distance to the moon varies during the course of it's orbit by a distance of 42,592 km (26,465 mi). When we speak of the distance to a body in space we are talking about an "average" distance and that is still just an estimation.

http://en.wikipedia.org/wiki/Lunar_distance_(astronomy)

How can we know that a certain galaxy is a specific number of light years away?

Interesting article, thank you for referring it to me.

 

[PureX]

You are talking about an experiment that can be conducted on earth, and that light is indeed received.

I'm talking about a distance astronomical object, like a star outside of our solar system for example.

I don't know that we would be able to send light to the moon and measure when we receive indication that the light has made it there and back?

In the case of the Moon, we have put mirrors there that will reflect a pulse of light sent to the Moon from the Earth, back to us on the Earth. By doing that, we can measure the time difference between the pulse of light reflected back, against when the pulse was sent. And then by relating that time to the distance between the Earth and the Moon (X2) we can get an idea how fast the light pulse traveled, there and back.

Knowing the speed of light, however, still does not tell us how far away a distant star is, though, because there is no way intrinsic to the light, itself, that will tell us how long it has been traveling (from which we could then determine the distances it has traveled).

So although I understand how we determined the speed of light, I still don't understand how we determine the distances between ourselves and other bodies in space.

 

[Jacob]

In the case of the Moon, we have put mirrors there that will reflect a pulse of light sent to the Moon from the Earth, back to us on the Earth. By doing that, we can measure the time difference between the pulse of light reflected back, against when the pulse was sent. And then by relating that time to the distance between the Earth and the Moon (X2) we can get an idea how fast the light pulse traveled, there and back.

We would need a measurement of the speed of light first in order to determine a distance this way. And, if we can do this experiment and if we have placed mirrors on the moon that can do this, we obviously know that we must of had an approximate to get there (or however we did it).

Knowing the speed of light, however, still does not tell us how far away a distant star is, though, because there is no way intrinsic to the light, itself, that will tell us how long it has been traveling (from which we could then determine the distances it has traveled).

So although I understand how we determined the speed of light, I still don't understand how we determine the distances between ourselves and other bodies in space.

You have verbalized my thought here, thank you.

 

[Stripe]

You are talking about an experiment that can be conducted on earth, and that light is indeed received.

I'm talking about a distance astronomical object, like a star outside of our solar system for example.

In an attempt to boil down your question, I said the key point was to determine the speed of light, which would allow us to determine how far light would travel in a year.

If your point is that the distance to stars is based on certain assumptions, you have no argument from me.

I don't know that we would be able to send light to the moon and measure when we receive indication that the light has made it there and back?

As Ha Nazir said, man has been to the moon and dropped mirrors on it. We can shoot lasers at those mirrors and detect photons making the return trip. Assuming constant lightspeed, this allows for very accurate measurement of its separation from the Earth.

 

[Stripe]

Knowing the speed of light, however, still does not tell us how far away a distant star is, though, because there is no way intrinsic to the light, itself, that will tell us how long it has been traveling (from which we could then determine the distances it has traveled).

So although I understand how we determined the speed of light, I still don't understand how we determine the distances between ourselves and other bodies in space.

There have been numerous methods described for how the assumption of a constant speed of light can be used to determine the distance to the stars.

 

[Jacob]

In an attempt to build down your question, I said the key point was to determine the speed of light, which would allow us to determine how far light would travel in a year.

Okay.

If your point is that the distance to stars is based on certain assumptions, you have no argument from me.

We would then be able to know how far light would travel in a year, under certain assumptions, but we would not be able to test our determination of this. We don't know anyone a light year away that would know when we emitted light toward them. Kind of a backward way of thinking about it now I know. Let's stick with what we know. You seem to do a good job of that.

As Ha Nazir said, man has been to the moon and dropped mirrors on it. We can shoot lasers at those mirrors and detect photons making the return trip. Assuming constant lightspeed, this allows for very accurate measurement of its separation from the Earth.

The speed of light is not affected by shooting. But I know what you mean if you mean directing the light toward a particular target.

 

[Jacob]

Stripe,

With the experiment you have pointed to thus far, how would the rotating object and sensors work in regard to measuring the speed of light accurately? How would the experiment be set up to assure an accurate measurement?

 

[Stripe]

Stripe,

With the experiment you have pointed to thus far, how would the rotating object and sensors work in regard to measuring the speed of light accurately? How would the experiment be set up to assure an accurate measurement?

I cant do a better job of explaining the experimental setup than the post Resurrected made that explained the experimental setup.

 

[CabinetMaker]

How do you know this?

Several years of physics in engineering school. I have also looked into several times since. Turns out the answer is not a simple yes or no type answer. You must deal with relativity constants.

Okay.

Would you say an orbital path could also be a moon around a planet or a satellite?

Yes moons and satellites orbit the earth and orbital mechanics allows to place satellites in an orbit that we choose.

A "wave" caused by a physical disturbance or the motion of the tides would be different. Can you explain a particle and a wave in reference to light?

As I said, light exhibits the properties of both a particle and a wave. I would suggest following this link. It has some pictures, videos and articles that explain it. Its long because scientists are still working on understanding it.

 

[Jacob]

I cant do a better job of explaining the experimental setup than the post Resurrected made that explained the experimental setup.

Okay.

I'm saying theoretically it sounds great but I don't know what would be involved to make the determination accurate practically, or if the experiment that presumably has been set up has actually been done. Or, the existence of a set-up indicates a result has been determined (at least once or multiple times). Has this experiment been completed and verified?

 

[Jacob]

Several years of physics in engineering school. I have also looked into several times since. Turns out the answer is not a simple yes or no type answer. You must deal with relativity constants.

Yes moons and satellites orbit the earth and orbital mechanics allows to place satellites in an orbit that we choose.


As I said, light exhibits the properties of both a particle and a wave. I would suggest following this link. It has some pictures, videos and articles that explain it. Its long because scientists are still working on understanding it.

Would you say that light can be modeled in terms of a wave, such that a width or length of period can be determined?

 

[PureX]

This site seems to be helpful.

I hadn't realized how difficult it is to determine distances in space. I guess I just hadn't thought about it, before.

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question39.html

 

[gcthomas]

We would need a measurement of the speed of light first in order to determine a distance this way. And, if we can do this experiment and if we have placed mirrors on the moon that can do this, we obviously know that we must of had an approximate to get there (or however we did it).

You have verbalized my thought here, thank you.

Radar measurements of the distance of the Moon don't require reflectors. Same goes for measuring the distance to Venus and some asteroids. The speed of light has also been measured since victorian times, and is very well known.

I have to say, none of your objections so far encourage me to think you have read any primers on the subject: are you really interested in finding out, or are you just pushing a preconceived notion that it's all rubbish?