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Solar Neutrino from Core to Surface
Name: Alex
Status: student
Age: 11
Location: N/A
Country: N/A
Date: 1/30/2004
Question:
How many seconds does it take for a neutrino to travel from the center to the surface of
the sun?
Replies:
Neutrinos go at the speed of light, which is about 186,000 miles a second.
The sun is about 800,000 miles across, so it's 400,000 miles from center to surface.
So it takes a little more than 2 seconds for a neutrino to get out.
Then it takes 8 minutes for it to get to Earth and fly through us, too. Just like sunlight, except it
doesn't stop here.
Jim Swenson
Since a neutrino has (almost) zero mass, it travels at the speed of light, which is 3 E 8 m/s =
300,000,000 m/s = 186,390 mi/s. The radius of the sun is about 7 E 8 m = 434,910 mi. Then using
the simple equation d = vt (distance = velocity times time), or t = d/v, the time is 7/3 s = 2.33 s.
This assumes the neutrino doesn't interact while travelling the 434,910 miles through the sun. In
fact neutrinos interact only very rarely (a light year of lead is needed to stop a neutrino) and this
allows us to study what is happening in the center of the sun only 8 minutes after it happens.
Since the earth is about 93 million miles from the sun = 93,000,000 mi = 1.5 E 11 m, it takes light
about 8.3 minutes to travel from the sun to the earth. So if the sun explodes, it will take over 8
minutes before we know!
Best, Dick Plano...
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Update: June 2012
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