Revision as of 00:32, 9 February 2012 edit 90.197.66.165 (talk) →‎Sun leaving main sequence between 1 and 5 billion years from now ← Previous edit		Revision as of 00:54, 9 February 2012 edit undo 90.197.66.165 (talk) →‎Sun leaving main sequence between 1 and 5 billion years from now Next edit →
Line 368: :I notice that neither this nor your previous query further up the page have yet been answered. To be honest, I started to yesterday, but then gave up because I found both queries too confusing. Each seems to have several intertwined questions, which makes the task of answering more daunting. Also, both are written in English sufficiently imperfect as to be difficult to understand. You might want to think a bit about exactly what you want to know, and then write one or more simpler questions, clearly separated. In the meantime, Section 5 'Life cycle' within our article [[Sun]] includes a graph which you might find helpful, though the concept of [[effective temperature]] is not wholly straightforward. :To address what I can: the Sun's radius will only increase to ''about'' 110% of its current value in 1 billion years from now, and to ''about'' 130% of today's value in 5 billion years from now. I'm sure that you can work out how much that will increase its [[Sphere#Surface_area_of_a_sphere\|surface area]], which is the main cause of its gradually increasing [[Stellar_luminosity#In_astronomy\|luminosity]] during the [[main sequence]] part of its lifetime, during which its surface temperature will remain ''roughly'' the same. Such modest changes in size are of course trivial compared to the distance of the planets from the Sun – for example, the Earth orbits the Sun at a distance of about 214 times (21400% of) the Sun's current radius. :When the Sun, now with a little less ~~heavy~~mass after 5 billion more years of fusion, leaves the main sequence and becomes a [[Red giant]], it will indeed grow to a size comparable to the size of the Earth's orbit (and will for this reason will become more luminous), but its surface temperature will also drop (lessening the increase in luminosity a little bit). Since the changes in mass and so on associated with these processes will, as you have already learned, cause changes to the orbits of the planets, it's difficult to calculate exactly where everything will end up, and I'm not familiar with the latest theories. Where the [[Habitable zone]] will be and whether any terrestrial-type planets will be in it depends partly on how you interpret that term: consider also that some moons of Jupiter and Saturn, for example are now thought potentially life-bearing right now, for reasons independent of Solar heating. :Hope this helps a little. {The poster formerly known as 87.81.230.195} [[Special:Contributions/90.197.66.165\|90.197.66.165]] ([[User talk:90.197.66.165\|talk]]) 00:32, 9 February 2012 (UTC)

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