Main sequence star to red giant?

The number changes depending on the starting mass of the star. Because its the stars' mass, and therefore gravity pressure, that causes the fusion reactions to occur at the core- the more mass, the more squeeze potential is available in the stars future.

If the star doesn't have enough mass, then when the star eventually uses up all of its hydrogen fuel, that's pretty much it! End of story. The star will collapse a bit... see if it has enough pressure to actually initiate heluim-helium fusion and if not... it dies as a white dwarf- slowly cooling to a ball of helium- or something.

If the star does have enough mass at its start, when the hydrogen fuel gets used up, the star will still compress when the hydrogen fuel is used up, but at some point, the pressure will get high enough to start helium-helium fusion, and the next stage of the stars life begins. Now, the star has to find its new 'balance', while the helium starts to fuse to the next stage of fusion.

By Balance, I means its diamater-surface area. This balance is achieved through a "push-of-war" Between the stars energy within trying to push everything out, and gravity trying to push everything in. Once everything stabilizes, it will turn out that the stars overall surface are is bigger than when it was burning hydrogen-hydrogen, as the helium-helium fusion reaction is more energetic- thus the "push of war" means that gravity cant push it in as much as it did in its first phase of life.

So, a Red Giant. Its bigger than a normal star, and red because- while the energy at its core is higher than a normal smaller yellow star, its energy is still diluted throughout its entire volume... so its in effect cooler than a yellow star.. thus redder.

Thats how a main sequence star becomes a Red Giant- those that are big enough to manage it. and yeah, thats what "Main Sequence" refers to: its the largest part of a stars life- the red giant stages are much much shorter in time (several million years) than its "Main Sequence" stage which can last for billions of years.

Less than a few thousand years.

"After the hydrogen fuel at the core has been consumed, the star evolves away from the main sequence on the HR diagram. The behavior of a star now depends on its mass, with stars below 0.23 solar masses becoming white dwarfs, while stars with up to ten solar masses pass through a red giant stage."

http://en.wikipedia.org/wiki/Main_sequence

"A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium."

http://www.astro.keele.ac.uk/workx/starlife/Starpa...

"A red giant is a luminous giant star of low or intermediate mass (roughly 0.5–10 solar masses) in a late phase of stellar evolution."

http://en.wikipedia.org/wiki/Red_giant

http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93R...

Pink giants are cooler than important sequence stars. Truly consider concerning the flame on a candle. Do not touch the fire seeing that it'll be sizzling. However a candle flame is cooler at the crimson section closer to the top, and the blue phase towards the wick is the most up to date. Blue is hot pink is cooler.