When did the first star appear?
You know, when people draw the Big Bang in cartoons, they often draw stars and galaxies appearing out of a big explosion. Actually, the matter that came out of the Big Bang wasn't stars yet at all, but rather a lot of particles and energy.
To get an actual star, first you need atoms, then molecules, then big clumps of matter drawn together by gravity. For a long time, about 400 million years, there was nothing like a star in sight.
After 400 million years stars formed, though they weren't quite the stars we see today. Instead, they were super giant stars called megasuns. These first stellar objects were a hundred times the sun's mass, and a million times as bright.
Astronomers see the effect of the megasuns even today when they look at the Cosmic Microwave Background Radiation, or the electromagnetic energy left over from the Big Bang.
The CMBR energy shows evidence of having been scattered off loose electrons. Those electrons were knocked off the gas that was floating around in the early universe by the enormous energy coming off these primordial behemoths, the megasuns!