Light year

[C1ay]

all these methods sound good, but there's no way to test them.

Test trigonometry? That is used out to 400 light years and your question was about one. Are you suggesting that we can't use trigonometry and the diameter of the Earth's orbit around the sun to calculate the distance to nearby celestial bodies?

[Tormod]

all these methods sound good, but there's no way to test them.

 

Yes, there is. These are standard tools of science and are easily tested. Verification is a problem. Testing is not.

[goku]

No, surveyors use parallax all of the time to measure distances to things they can't access and don't already know the distance to.

the ones i've seen use radar, i think. i guess it's more accurate :)

[goku]

Test trigonometry? That is used out to 400 light years and your question was about one. Are you suggesting that we can't use trigonometry and the diameter of the Earth's orbit around the sun to calculate the distance to nearby celestial bodies?

trigonometry might work as long as our sun and the star are both stationary.

[goku]

wait a minute! you've got me off subject

light year

[rockytriton]

ok, the ratio of the opposite over the adjacent (the tangent) of an angle is the same no matter what the distance, this has been proven mathematically. Are you saying that you wouldn't believe it true for a 1 billion mile length because it can't be done physically?

[goku]

ok, the ratio of the opposite over the adjacent (the tangent) of an angle is the same no matter what the distance, this has been proven mathematically. Are you saying that you wouldn't believe it true for a 1 billion mile length because it can't be done physically?

:)

see post #21

[Bo]

by your logic also 2.47493949 meters might not exist, since noone has (presumably...) ever measured exactly that distance. It is however a fair principle to say that (without quantum effects) arbitrary distances can exist in a continuous space.

 

the same with the light year: light has a known speed, so we know that in a certain time interval light travels a certain, known, distance. that this distance s not measured doesn't say it doesn't exist.

 

Bo

[goku]

by your logic also 2.47493949 meters might not exist, since noone has (presumably...) ever measured exactly that distance. It is however a fair principle to say that (without quantum effects) arbitrary distances can exist in a continuous space.

 

the same with the light year: light has a known speed, so we know that in a certain time interval light travels a certain, known, distance. that this distance s not measured doesn't say it doesn't exist.

 

Bo

the only thing that makes us think that light can travel for years is the theory that the stars are light years away.

circular :) reasoning??

[rockytriton]

sometimes I wonder if you are serious or if you just like to make people crazy. By the way, your post #21 makes no sense, so that didn't answer my question.

[goku]

sometimes I wonder if you are serious or if you just like to make people crazy. By the way, your post #21 makes no sense, so that didn't answer my question.

is our sun moving?

are the stars moving?

is it easy to calculate distance of objects useing trigonometry while they are in motion?

[Tormod]

the only thing that makes us think that light can travel for years is the theory that the stars are light years away.

circular reasoning??

 

That the stars are light years away is not a theory, it is something we observe with our current tools. There is no circular reasoning.

 

A light year is of course a distance - the distance light will travel in empty space in one year.

 

We know that the Earth - Moon distance varies from 385,000 kilometers to 405,000 kilometers (approximately). How can we relate this to light? Easy - we can measure the time it takes for a signal to bounce off the moon and come back.

 

Measuring distance this way is very simple. Like with the space probes in orbit around Mars - the time it takes for a signal to be sent there and returned is exactly twice the distance between Earth and Mars at the time.

 

Measuring distance in light years using this method is slightly more difficult because we cannot currently send space probes to even the closest star. We have however sent probes that are currently at the edge of the solar system (the Voyagers) and we can still hear faint signals from them, even at distances of over 8.7 billion miles.

 

If radio signals can travel that long, then light can too, because they are essentially the same thing.

 

More about the Voyager missions:

http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html

[Tormod]

is our sun moving?

are the stars moving?

is it easy to calculate distance of objects useing trigonometry while they are in motion?

 

the motion is so slow compared to the distances involved that they make no difference to the end results.

[rockytriton]

is our sun moving?

are the stars moving?

is it easy to calculate distance of objects useing trigonometry while they are in motion?

 

yes

yes

absolutely, especially since they are moving on a known function.

[Bo]

the only thing that makes us think that light can travel for years is the theory that the stars are light years away.

circular :) reasoning??

No. the thing that makes us think light can travel for years is the notion of conservation of energy. and you probably also need compactness of space (which means as much that there are no "holes" in spacetime).

 

Bo

[Boerseun]

Let's forget about extrasolar stars for a second, and look at the sun.

 

That sucker's 8 light-minutes away, which plugs into your argument of a light-year; we'll just replace light-year with 8 mintues.

 

Who's to say light can travel 8 minutes? Do you doubt for a second the distance of the sun? Nobody's actually taken a measuring tape and measured the distance to our closest star, which is only 8 minutes away. So - let's assume light can't travel 8 minutes. Then, say, the sun is 7 light-minutes away. And then we repeat the argument. Who's to say light can travel 7 minutes? And the argument repeats, ad infinitum, (well, not infinitum - just now the sun is sitting on your lap by this reasoning).

 

My point is this - light travels at a finite, measurable speed. Using this, parallax, redshift, etc. we can determine the distance of stars and galaxies. There's no difference in the argument whether light's travelled for eight minutes of for eight years. Your argument is based on 'a year', which is a subjective Earth-bound human experience, and holds zero sway in the galactic scheme of things. The moment lightspeed goes down from 'infinity kms/hour' to anything less than infinity your question becomes meaningless.

[Erasmus00]

test it on a star and see.

but then you must first know how far away the star is.

maybe flawed, maybe not :)

how can we know?

 

Test it on something on your desk. Then test it on the tree outside your house. Then test it on the water tower on the horizon. Go to longer and longer length scales. The moon perhaps. If it works there, why not elsewhere?

-Will