When a star becomes a red giant, how long is it since it starts to expand until it reaches its maximum radius?

And can you immediately tell that the star has started to expand?When a star becomes a red giant, how long is it since it starts to expand until it reaches its maximum radius?There isn't a definite answer to this considering the wide range of possibilities in stars. However the red giant phase is very short lived, mainly because it is more of an explosion in the star that dies down quickly. This site:



http://cse.ssl.berkeley.edu/bmendez/ay10鈥?/a>



cites the time spent on the red giant branch as on the order of a million years or so. That means from the time it starts to expand until the end of it's expansion (also known as the helium flash) it is only a few million years for a typical star. This is much less than the time it spends on the main sequence which can be on the order of 1-10 billion years or more. You can read more about the general evolution of a main sequence star here:



http://outreach.atnf.csiro.au/education/鈥?/a>When a star becomes a red giant, how long is it since it starts to expand until it reaches its maximum radius?There's a problem that could make predicting the timing within 1000 years impossible even if we knew the measurements within 0.0000000000001%. The best way to understand it is this. If 100 tires were constantly inflated until they all popped, and they all began simultaneously, the first one to pop is going to be at least 10 seconds earlier than the last. Now imagine red giant stars hundreds of millions of miles across. They are over 1,000,000,000,000,000,000,000,000,000,00鈥?times larger in volume. So imagine how long apart THEIR ends could be. Thousands of years at least. So even if we knew the exact measurements, it would be impossible to predict the length of the cycle in time.