gcthomas
New member
Correct. The law is a geometrical one and doesn't depend on the qualities of the light. Light behaves the same everywhere and at all times, that is how it can tell us the distances of things.
How are light-years measured?
- Thread starter Jacob
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Correct. The law is a geometrical one and doesn't depend on the qualities of the light. Light behaves the same everywhere and at all times, that is how it can tell us the distances of things.
gcthomas
New member
From what I remember, 1 AU is 496 light seconds, so it is only 500 to ~1% precision. The only thing contrived is your post, I'm afraid.
Jedidiah
New member
149,597,870,700 meters / 299,792,458 meters per second = 499.00 seconds
We're both wrong.
You were four times more wrong than me. :dizzy:
gcthomas
New member
149,597,870,700 meters / 299,792,458 meters per second = 499.00 seconds
We're both wrong.
You were four times more wrong than me. :dizzy:
Fair enough. :up:
But if it was 500.000 light seconds seconds, I'd be more impressed with the coincidence!
What do you mean by the behavior of light?
I believe you would point out that a laser beam is directed, but that the light that is "directed" is no different from other light of the same wavelength.
Stripe said something about shooting a laser.
A particle of light. That behaves like a wave.
A photon is an elementary particle, the quantum of light and all other forms of electromagnetic radiation, and the force carrier for the electromagnetic force, even when static via virtual photons.
I am thinking light can be modeled in terms of waves and particles as a photon?
http://en.wikipedia.org/wiki/Light
"Like all types of light, visible light is emitted and absorbed in tiny "packets" called photons, and exhibits properties of both waves and particles."
That is our best understanding at present.
How is light measured?
We measure its intensity, its wavelength, its speed in various media. What specifically are you asking?
I'm not sure. Now I am noticing that we measure light though the discussion was on using it to measure other things, which I saw as improbable in feasibility.
A light year is a unit of defined unit of measure. That's all it is. If you take the speed of light times the number of seconds in a year, that is how far light will travel in one year. It is a convenient form of measurement gien that the distances being measured are so great.
| As defined by the IAU, the light-year is the product of the Julian year[note 2] (365.25 days as opposed to the 365.2425-day Gregorian year) and the speed of light (299792458 m/s).[note 3] Both these values are included in the IAU (1976) System of Astronomical Constants, used since 1984.[3] From this the following conversions can be derived. 1 light-year = 9460730472580800 metres (exactly) ≈ 9.461 petametres ≈ 5.878625 trillion miles ≈ 63241.077 astronomical units ≈ 0.306601 parsecs |
We use other properties of light and known reference objects to estimate the distance between Earth and the the lights source. The resulting distance is given in light years.
Not only is it feasible to use light to measure distances, it is the only option for distant objects. Consider that a laser aimed at the moon spreads out some 200km by the time it gets there and only a tiny tiny fraction is actually reflected back. Can you imagine how much spread would occur if you aimed light at Proxima Centauri which is 4.2 light years away? We can't bounce a laser light or a radar beam off of anything so we have to look at the light emitted by the distant source.
A unit of measure is not necessarily a unit to measure with or a unit to measure by. In terms of the speed of light or a measure of the (traveled?) distance of light we can describe how far away a given thing is with it, but we probably determined the distance with something else.
It seems silly to say we can measure how far away something is by saying that it was faint.
A star cannot reflect the light of a laser, for instance.
I hope you can see I am following what you are saying, albeit in my own way.
This is EXACTLY what a unit of measure is. An inch. A foot. A centimeter. A meter. We use them to measure how far away something is all the time. Its a 100 miles to home. The US is about 2,800 miles wide. It is a defined unit that we use to convey information regarding distance.
We determined the distance based on the light we received. There is nothing else. (Except for gama ray and some other forms of radiation. Which are light at different frequencies.)
You do this every time you drive at night.
Nope. But it emits massive numbers of photons, light.
I think you are trying but I think you are getting hung up on definitions. The light emitted from a start is not the "same" light used to measure a light year. A light year is just a REALLY long ruler. We use it to describe hoe far the light emitted form a star has traveled to reach Earth.
That's just it, a light year is not a ruler (as stated by someone else earlier in this thread). I know we must ask HOW we measure if it has been determined (erroneously or not) that a light year is a unit of measure to measure something with/by.
If we have converted a measurement to light years, that is another matter. But then we would ask how we know the measurement was true or accurate.
That person was wrong. A light year is a "ruler" in the sense that it is used solely as a measure of distance.
Again, you are confusing the HOW of distance measurements with the UNITS of distance measurements. There have been several links posted on this thread regarding how the distance to stars are measured. Have you read any of those links?
Yes, that question is asked all the time, is our measurement true and accurate? Scientists are always working to refine the measurement methods to make them more accurate.
gcthomas
New member
And yet it is a very reliable method.
If you move a lamp four times further from the wall it will illuminate the wall with one sixteenth of the intensity. It is just simple geometry, and it works for stars - of you have two stars with the same luminous output and you measure the ratio of their apparent brightnesses then the square root of that ratio is the ratio of their distances.
You can estimate a speaker's distance from you from the received volume of their voice - of he sounds quiet then he is far away. Same principle.
A measure of distance, or a unit, is different from a measurement of distance. The measurement requires something by which to measure.
I have visited every website mentioned in this thread. Parallax has been proposed as a good way to measure a distant star (which is really a near star, just not the sun). I have not seen how the distance to a star has been measured.
What about when someone says a light is brighter than another light? I'm speaking a a light such as you would find in a house.
Are you talking about determining a proportion or are you talking about light intensity or are you talking about something else?
Such as a ruler. Or a light year. ANY distance can be measured in feet or light years. There are times when one is more convenient than the other, but both are perfectly valid units for expressing any distance.
One method used is parallax.