Tips & History.... Astronomy
The reason has to do with a sub-atomic particle called a neutrino. Neutrinos have no electrical charge and virtually no mass. As a result. they can pass through most forms of matter unchecked - a property which makes them extremely difficult to detect. Most of the radiation generated at the Sun's core is absorbed by the Sun's surface layers.
Neutrinos, however, once created, are unaffected by the outer layers and so provide a direct indication of the activity in the core. Neutrinos are also largely unaffected by the Earth, so most pass straight through without even slowing down. But they can sometimes react with atoms of chlorine-hence the tank of cleaning fluid which is rich in chlorine.
By monitoring the reactions in the tank, scientists can gauge the number of neutrinos reaching the Earth, and thus the number being produced by the Sun. The tank has to be so far underground in order to block cosmic rays which would otherwise swamp the neutrinos' effects.
Neutron stars are believed to be the remnants of large stars which have erupted as supernovae at the end of their lives. Their intense gravity has the effect of concentrating the powerful radiation they give off into beams. Since many neutron stars also spin, the radiation sweeps across space like the beam from a lighthouse. As the beams flash past Earth, the star seems to pulse with energy-which is why rotating neutron stars are known as pulsars.
If the call were routed around the surface of the star, your voice would take an hour and a half to get through. Some astronomers believe that a mysterious and invisible object in the stellar group known as Epsilon Aurigae may be still larger. The object has not been seen directly but every so often it seems to cause a partial eclipse of its visible neighbour for a staggering two years at a time. By observing these effects, some astronomers calculate that, if the object is a star, it may be more than 3000 million km (2000 million miles) across-large enough, if it were in our solar system. to engulf all the planets out to Saturn.