Hi All As most of us know, in a qualitative sense, the Sun will eventually become a Red Giant before its core explodes (the Helium Flash) and it's heaved onto the Helium Main Sequence, to shine merrily for about 100 million years. What I want to know, in a quantitative sense, is just how its luminosity behaves with respect to time as it's approaching the Red Giant Tip - its point of maximum luminosity before the Helium Flash. From all the graphs of luminosity against that I've seen that final phase is very rapid compared to its luminosity evolution for the 12 billion years prior. Is there a function that fits that final phase? Any good references?