You hear about the supernovas, but do stars necessarily have to age for them to explode? For example, could our Sun suddenly lose it? :eek:
Oh great. Now I have something else to worry about :smack: 
There is no evidence to support that it would. Whenever we see a supernova, astronomers always dig up old images of that part of the sky to try to find the progenitor star, before it exploded. When they do, it’s always an old one. And there’s no known theoretical mechanism by which a young or middle-aged star could suddenly go nova. So no, Thin Lizzy doesn’t have something else to worry about.
Also, our sun is too small to become a supernova. So all you’d have to worry about is expansion into a red giant consuming the Earth. Hardly worth mentioning, really.
So how long does it take between the time it start expanding and the time it engulfs the Earth?
Doesn’t a star only go supernova once all the hydrogen and helium have been fused?
Our sun won’t go nova but what about the helium flash? I know this is supposed to be a sort of explosion but I have no clue how powerful it is (it will not destroy the core I know but would it affect the earth?).
After helium fuses into carbon I think our sun is done. I do not think it can manage to fuse carbon. A planetary nebula will form as the sun’s outer layers drift away leaving a white dwarf. The white dwarf glows from heat but is not activley fusing anything. Eventually it will cool off and be a black dwarf…essentially a cold lump of carbon floating about.
A larger star can fuse all the way up to iron but iron is a net energy loser in fusion. It is here you get the supernova. The core will continue to collapse as no fusion in the iron initiates to make a repulsive force. Eventually the repulsive forces of the atoms is more than the gravitational contraction. BOOM
There is an exception to the aging star running out of fuel scenario but it doesn’t have any application to our sun:
The part below about Type 1a supernovae goes into more detail about accretions.
For those interested a really good book on the sun is George Gamow’s The Birth and Death of The Sun. Gamow was a top-notch scientist (for example, the Big Bang theory) and an interesting and entertaining writer.
OK, maybe the Earth being engulfed wouldn’t be ALL you’d have to worry about. The world supply of ice cream would probably melt, too.
According to my astronomy teacher, the Sun’s output is steadily increasing as it ages. This will eventually result in “thermal runaway” on the Earth, when it is no longer able to handle the increased energy input from the Sun, turning it into a Venus-like inferno.
The end may be nearer than you think.
I’m far too busy (and, let’s not forget lazy) to dig up a cite, but I remember from a film in my AP Physics class that said that by the time the Sun expands to a red giant, all life on Earth will have died. It was quite the cool looking computer graphics (like CGI, but 90’s style). Anyway, they estimated 5 billion years (sorry, no cite) for the Sun to go red giant. I believe it was the same film that said that Earth will have cooled off by then. My memory fails me as to why the Earth would no longer be habitable.