1. Comets are visible at regular intervals because they orbit around the sun, like Earth. As they get closer to the sun, their ice layers begin to melt off, leaving a tail behind it.
2.The largest stars are usually red hypergiants. VY Canis Majoris is the largest star ever seen. It is a red hypergiant, approx. 1-2000 times the diameter of the Sun.
3. When the sun is about ten billion years, it will begin to burn helium, causing it to expand into a red giant, engulfing Mercury, Venus, and maybe Earth. It will burn its helium for about two billion years before beginning to puff off its outer shell, leaving behind a small, dense white dwarf.