What Is a Light Year? Understanding the Value of 1 Light Year

AI Thread Summary
A light year is defined as the distance light travels in one year, approximately 9.5 trillion kilometers or 5.88 trillion miles. The concept of light years serves as a measure of astronomical distances, independent of the observer's frame of reference due to the constant speed of light. Discussions highlight the importance of relativity in understanding measurements between different observers. Calculations demonstrate that 1 light year can be expressed in various units, including meters and feet. Overall, the light year is a critical unit for measuring vast distances in space.
lakshmi
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what is the value of 1 light year
 
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lakshmi said:
what is the value of 1 light year
It is the distance light travels in one year. It, in itself, is a measure of distance so perhaps you're interested in converting this to meters? Miles?

Pete
 
pmb_phy said:
It is the distance light travels in one year. It, in itself, is a measure of distance so perhaps you're interested in converting this to meters? Miles?

Pete

A measure of distance? How can light speed be an accurate measure of distance when it travels with respect to an observer?
 
GOD__AM said:
A measure of distance? How can light speed be an accurate measure of distance when it travels with respect to an observer?
'distance' as in 'within your own frame of reference' (or one not in relative motion to yours); to obtain a value for the distance as observed by someone in a different frame, just apply Relativity!
 
The valua at which light travels in a year is approx. 9,500,000,000,000 kilometers.
 
GOD__AM said:
A measure of distance? How can light speed be an accurate measure of distance when it travels with respect to an observer?
Because the speed of light is independant of the observer. Therefore since all observers measure the same speed of light, 1 light year is a well defined quantity (although different observers measure different distances between events, but that's a whole different topic).

Pete
 
Here is the full Calculation:
v=\frac{d}{t}

d=vt
d=cy

d=(3.0*10^8\frac{m}{s})(3.15*10^7\frac{s}{year})(\frac{1km}{1000m})

d= 9 460 800 000 000km
 
decibel said:
The valua at which light travels in a year is approx. 9,500,000,000,000 kilometers.
I think that you are taking liberties with the meaning of the word value.
 
GOD__AM said:
A measure of distance? How can light speed be an accurate measure of distance when it travels with respect to an observer?

Take a look at the defintion of the SI meter sometime
 
  • #10
Here's a nice order of magnitude calculation. (No calculators needed.)

1\ yr \approx \pi\times 10^7\ s
c \approx 3\times 10^8\ m/s

1\ light\ yr=(c)(1\ yr) \approx (\pi\times 10^7\ s)(3\times 10^8\ m/s)=3\pi \times 10^{15}\ m

You can work out the analogous approximation in feet using
c \approx 1\ ft/ns
 

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