What's the reason for this? I vaguely recall reading once that it was to do with the build-up of helium in the core, but I can't remember and I haven't been able to find the reason since.

Any ideas?

I have not followed that one but for some reason I came to believe that it was another wackado theory and that there was no truth to it. I think richard c hoaxland was promoting it. IIRC
edited for typos/srr

Oh no, I'm sure it's an actual phenomenon.

Perhaps I discounted it due to the source. Imagine that. :D

Oh dear. How very unscientific of you. I won't tell Duendy if you don't.

What's the reason for this? I vaguely recall reading once that it was to do with the build-up of helium in the core, but I can't remember and I haven't been able to find the reason since.

Any ideas?


Your memory serves you well...When hydrogen becomes helium during the fusion process in the Sun's core, it takes up less space. The core shrinks and this shrinkage increases the pressure in the core making its temperature increase. This increased pressure and heat from the core causes the gas pressures in the outer envelop to also increase, so it expands to remain in equilibrium. The nuclear reaction rate is very sensitive to temperature so that even a slight increase in temperature makes the nuclear reactions occur much more quickly, therefore making it brighter. Keep in mind this heat is at the core, the outer envelop actually gets cooler due the the gases dispersing during expansion.

Also! The sun's luminosity is it's mass to the power between 3-4. So therefore even a slight increase in the sun's size will have a great impact on its luminosity.

Honors E.S. For ya. =)

Thank you for clearing that up. Now I can sleep soundly tonight.

Your memory serves you well...When hydrogen becomes helium during the fusion process in the Sun's core, it takes up less space. The core shrinks and this shrinkage increases the pressure in the core making its temperature increase. This increased pressure and heat from the core causes the gas pressures in the outer envelop to also increase, so it expands to remain in equilibrium. The nuclear reaction rate is very sensitive to temperature so that even a slight increase in temperature makes the nuclear reactions occur much more quickly, therefore making it brighter. Keep in mind this heat is at the core, the outer envelop actually gets cooler due the the gases dispersing during expansion.

Also! The sun's luminosity is it's mass to the power between 3-4. So therefore even a slight increase in the sun's size will have a great impact on its luminosity.

Honors E.S. For ya. =)

Just out of curiosity, what is the annual slight increase in the sun's size? Is it measurable and if so, what is the so-called scientific measurement process? :D

Just out of curiosity, what is the annual slight increase in the sun's size? Is it measurable and if so, what is the so-called scientific measurement process? :D

It's called the largening. Of course it's measurable, ...stand outside 12 noon each June 1st, stare directly into the sun for 30 seconds, close your eyes immediately, and count the number of dots you're seeing. For each dot you see that wasn't there the previous year, you add an inch to the sun's circumference. I forget the exact name of the measurement process -- although the pinpupil method sounds right. I thought this was common knowledge...sheesh. Well, always glad to help.

It's called the largening. Of course it's measurable, ...stand outside 12 noon each June 1st, stare directly into the sun for 30 seconds, close your eyes immediately, and count the number of dots you're seeing. For each dot you see that wasn't there the previous year, you add an inch to the sun's circumference. I forget the exact name of the measurement process -- although the pinpupil method sounds right. I thought this was common knowledge...sheesh. Well, always glad to help.

Based on your reply, sounds like you've been adding the 'Jim Beam' factor in with your 'pinpupil' sun diameter dot measurement process....Right? Pretty scientific process you've got there. You should publish it. Maybe the Skeptical Inquirer would be interested in hearing about it or at the very least, Jim Beam would........ :D

IIRC, it has to do with the gas laws, fusion causes a decrease in the total number of nuclei in the core, causing the core to shrink and heat up.

This interisting to me from an astrobiological standpoint because it causes the inner edge of the habitable zone to migrate outward slowly, and that inner end is getting pretty close to Earth right now. :eek: The Earth has compensated for the brightening Sun by taking CO2 out of the atmosphere and traping it in limestone, the CO2 levels are already extremely low (even with the human-caused increase), and once it hits 0 the CO2-carbonate buffer quits working, and you can say "hello moist greenhouse effect"!