For more information about this recent event, see a NASA article about it. There are currently many satellites observing the sun, and there is a lot of information available about it. You can also get a compilation of current solar images from many satellites in different filters including highly-ionized iron. There is also apparently a new IMAX movie called SolarMax . Next, we started talking about stars , and we will continue to talk about, first the properties of stars, then the formation, evolution and death of stars, in the coming lectures.
Luminosity is defined as the amount of energy emitted from the whole star in one second.
Take care not to confuse luminosity with brightness , where brightness means how bright the star appears to be or you measure the star to be. The luminosity is an intrinsic or objective property of the star, and the brightness is an apparent or subjective property of the star. The way this works is that the star emits its light in all directions summing up that emission over all directions gives the luminosity. On the other hand, on earth we have a detector, and it can only sample the luminosity of the star coming in our direction. That detector has a certain area, and so how bright we measure the star to be depends on how far away from it we are.