How far the light can be shine?

[zyx_oay]

light can be speed faster about 300,000 km/s,
but how long the distance that light can be arrive?

 

[pam]

You can see stars, can't you?

 

[dst]

Any distance until it interacts with something.

 

[Parlyne]

We've observed objects as distant as about 13 billion light years. So, we know of light that has traveled that far. (For reference, 13 billion light years is a little more than 1.2*10^26 meters. That's 120 trillion trillion meters, which is about 75 billion trillion miles.)

 

[jobyts]

We've observed objects as distant as about 13 billion light years. So, we know of light that has traveled that far. (For reference, 13 billion light years is a little more than 1.2*10^26 meters. That's 120 trillion trillion meters, which is about 75 billion trillion miles.)

How do the scientists conclude that the particular light we received is x years old?

 

[dipstik]

light year rings...

i would imagine triangulation and knowing the speed of light would be an unrealistically simple way of doing it...

 

[dst]

How do the scientists conclude that the particular light we received is x years old?

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970415c.html


Doesn't sound all that precise to me, parallax aside?

 

[robertm]

Inertia still applies for EM radition, so i believe it depends entirely upon the environment into which you are shining the radiation. Since the majority of space is nearly a perfect vacuum EM radiation will countinue along its original vector until acted upon by an outside force ie... black hole, nebula, telescope ect. Someone please correct me if I am wrong.

 

[russ_watters]

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970415c.html


Doesn't sound all that precise to me, parallax aside?

Most of those methods are highly accurate, especially since stars tend to fit a very tight band of types.

Note, though, that those methods are used for stars in our galaxy. For more distant stars/galaxies, they use redshift, type 1a supernovas, and cephid variable stars (for really nearby galaxies).

 

[russ_watters]

Inertia still applies for EM radition, so i believe it depends entirely upon the environment into which you are shining the radiation. Since the majority of space is nearly a perfect vacuum EM radiation will countinue along its original vector until acted upon by an outside force ie... black hole, nebula, telescope ect. Someone please correct me if I am wrong.

Inertia is a property of mass, so it doesn't apply to light, but otherwise yes, it is similar to Newton's first law - if nothing gets in the way, it'll keep going essentially forever. The Hubble has taken pictures of objects 13 billion light years away.

http://hubblesite.org/newscenter/archive/releases/1997/25

 

[dst]

Most of those methods are highly accurate, especially since stars tend to fit a very tight band of types.

Note, though, that those methods are used for stars in our galaxy. For more distant stars/galaxies, they use redshift, type 1a supernovas, and cephid variable stars (for really nearby galaxies).

Oh right, well I wouldn't know

 

[leftyguitarjo]

Most of those methods are highly accurate, especially since stars tend to fit a very tight band of types.

Note, though, that those methods are used for stars in our galaxy. For more distant stars/galaxies, they use redshift, type 1a supernovas, and cephid variable stars (for really nearby galaxies).

they use the supernovae as a reference because of how much light it emits, right?

 

[f1flagger]

... black hole, nebula, telescope ect.

And eyeballs: if a photon manages to travel anything like a billion trillion miles I'd rather catch it with my eye than a ccd.

 

[Andy Resnick]

How do the scientists conclude that the particular light we received is x years old?

Indirect methods. One way is to measure the redshift- how far a particular emission line has been skewed. The age of the universe is determined, in part, by the redshifted background radiation (the 4 K noise).

Another way, as russ mentioned, is using "standard candles". These are sources that we "know" emit a certain amount of light:

http://csep10.phys.utk.edu/astr162/lect/cosmology/cosmicd.html

Parallax measurements are good only for very close objects.