Light

John Russell · Post by **John Russell** » Wed Apr 18, 2007 1:06 pm

When someone turns off a flashlight, does the light that has been sent continue to go out into space? E.G. When a star no longer exist, do we continue to see the star millions of years later, assuming it was millions of light years away?
Thank you for the consideration.

John

makc · Post by **makc** » Wed Apr 18, 2007 3:22 pm

why not? is a flashlight supposed to suck its light back into itself once it's switched off?

John Russell · Post by **John Russell** » Wed Apr 18, 2007 3:41 pm

When I use a hose for water, when the source is cut off, so is the stream of water. What does light use as an energy source once it is cut off?

NoelC · Post by **NoelC** » Wed Apr 18, 2007 6:53 pm

John Russell wrote:When I use a hose for water, when the source is cut off, so is the stream of water. What does light use as an energy source once it is cut off?

Actually, the stream that has already left the nozzle continues after you cut it off. It is traveling under its own kinetic energy, which was imparted at the nozzle when it left the hose.

-Noel

BMAONE23 · Post by **BMAONE23** » Wed Apr 18, 2007 9:10 pm

Super Nova 1987A or SN1987A became visible to us in 1987 (20 years ago) but the event happened 168,000 years ago. In 1986, the star still looked like a star to us even though its's death had already occured appx. 167,979 years earlier. http://heritage.stsci.edu/1999/04/sn1987anino.html
So even if a star had "winked out", we would continue to see it as is was until the event light reached us.
You're flash light analogy is a good one though. If it were the only light source, it would remain visible until the "turning off" light curtailment event passed by the alternate observation point.

Realistically though, it would be overpowered by other, brighter sources and be lost to their light, like that of the sun or another star.

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