I am saying that making a units conversion to light years is different than saying you can measure a light year.
I have not seen it used.
What other methods would you say there are?
How are light-years measured?
- Thread starter Jacob
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What other methods would you say there are?
If I am understanding you correctly, your main complaint seems to be that since we don't have a ruler one light year long, we can't measure a light year?
Do you work in a field where parallax is needed to measure anything? I don't so I have not seen it used either. That does not mean that it is not used. By that loick, we can't measure a mile because we don't have a ruler 1 mile long.
The links below will take you to descriptions of various common methods.
The assumption was that we measure a light year by the light we receive, such as into our eye or with some kind of measuring instrument.
The objection about not having a ruler was raised here in this thread.
Do you think that apparently the distance the earth travels in a half year is far enough for parallax to actually work?
Ah ha! I see the problem. The assumption you made is absolutely incorrect. We do not measure by the light received. A light-year is defined unit of length based on the speed of light and time. Speed times time equals distance. Its that simple. The light we see in the telescopes must be analyzed using other methods to determine the distance it traveled.
A ruler is not needed to measure distance. An accurate speedometer and stop watch will work. Geometry will work.
In some but not all cases.
You have an equation. In terms of measuring...
Express it as a function and tell me what the input variables are and what is the function output, if you could please?
I don't know that it does.
Distance = Velocity * time
Let the magnitude of the velocity = c (We don't care about direction)
c=186,282 miles per second (299,792 kilometers per second)
Let time = 1 year. Since or speed is in miles per second we need to find out how many seconds in a year.
1 year*(365.25 days/year)*(24hrs/day)*(60min/hr)*(60sec/min) = 31,557,600 seconds
So, Distance = speed * time = 186,282 miles/second*31,557,600 seconds = 5.87849981 × 1012 miles
That is how far light will travel in one year hence the term light-year as a unit of measure. The conversion factor is:
1 light-year = 5.87849981 × 1012 miles
That is your challenge. Links have been provided. If you were one of my college students I would tell you it is time to do your homework.
Right, you have these equations or expressions in terms of units or units of measurement and being consistent with them. But I still don't know how old the light is that I am observing when I look into the sky at night.
I looked at your links (already). I took Calculus based Physics when I was in college, but my care with units began with Chemistry and continued with Physics and Astronomy in High School.
If you look at Proxima Centauri then the light is about 4.2 years old. You would know that because we know that is how close that star is. If you don't know what star you are looking at you have no way to know how old the light is.
Thinking of how old the light is doesn't help anyway. Light does not age. The reason it falls off as 1/r^2 is because as the distance you are away from the source, the fewer photons you can detect because the area illuminated by those photons gets progressively larger with distance.
First, in looking at any given star do we know how far away it is to determine how old the light is?
That is one view about light and age.
This sounds great theoretically. But the question is (was... remember, Astronomy) what is a photon and can you measure a photon or photons?
Yes, through the methods already linked too.
Photons don't change as they age.
Can you see? The photons are striking the retina of your eye. Can you take a picture? The photons strike the film and leave an image. When you look into a telescope the photons leave an impression on your eye or a film plate. Yes, can use a photon to perceive light.
Can you actually measure a photon itself? Irrelevant to the discussion at hand. That us a completely different branch of physics.
gcthomas
New member
CM is right, since a light year is not a measurement of time, but is simply a conveniently large number of metres. Forget the word 'year' on the unit name - it is causing you to focus on the wrong concept. It is simply a unit like the mile, which is itself based on a thousand Roman legion paces, and you would be quite happy to measure miles driven without worrying that you weren't counting paces.
It is also interesting to note that photons CANNOT show evidence of aging. They travel at the speed of light so time dilation effects mean that they don't experience the passage of time.
Was it physics or counting photons that they might be on a film plate or rather perceived physically and communicated electrically somehow? Then the question of what is a photon. If it can only be a measurement, is it then a particle or not?
Do we know of ANYTHING that is a light year away, is the problem. If we use that unit of measure (or, rather... that unit), how did we come to do so and is it right to do so?
Why don't you tell us what a photon is. You have been provided with several links that describe what science understands about the duality of light. We see because our eye receive photons and our brain processes them. We have light meters built into cameras that measure the amount of available light so that we can set shutter speed and aperture for getting a properly exposed picture.
That science does not have a perfect understanding of the exact nature of light does not mean that we can not measure things about it.
My understanding is that a photon is measured on a photon plate used in astronomy. Is it true? Is it true that one "hit" transferred or communicated as an electrical impulse, translates to "one photon" or has this ever been a measure?
Perhaps we had more to work on in our observatory in High School (over 14 years ago for sure).
I don't know. The energy contained in one photon is very small. It may take a large number of photons striking a plate to make an electrical impulse.
Our school did not have an observatory nor have I taken astronomy. I have worked with solar panels that convert light energy to electricity. I don't recommend them. Grossly inefficient.
gcthomas
New member
I know what a metre is, and a light year is just 9,460,536,207,068,016 metres. When you calculate distances you don't do it in light years - you do it in parsecs or metres and convert it to light years for popular consumption. Scientists don't really use light years for technical work as it is not a standard unit.
Thank you for all you have said.
This is getting at something. But I don't remember what a parsec is. I feel I have heard of it before.
Does untellectual sound bot-like to anyone else?