There are many neutrino sources, although supernovae may be the most prevalent with 99% of energy released as neutrinos vs 1% as visible light.
Our sun radiates about 2% of its energy as neutrinos.
They travel at the speed of light and rarely interact with normal matter. So rarely, in fact, that 99.99% of neutrinos would pass through a 10km-thick slab of lead.
Most neutrinos pass through the entire earth without hitting a thing.
1021 nuetrinos pass through each 1" x 1" area of your body per second and, on average, you have a 25% lifetime chance of interaction with a neutrino particle.
Here are some neat neutrino facts:
Who knows what will be discovered!