Stars, Energy & Einstien

[Brian]

Einstien figured out that matter and energy were two forms of the same thing, right? Then they made a nuclear fision reaction and proved it, right? Nuclear Fusion followed.
Before the early part of the last century, how did they think the sun produced energy?
Just curious.

 

[Luke T.]

http://www.curtin.edu.au/curtin/dept/phys-sci/sun/energyhs.htm

 

[Dancing David]

Kelvin figured out that it couldn't be just gravitational friction(okay maybe it wasn't Kelvin).
It didn't take long for people to eliminate chemical reaction.

That was just one of many problems solved in the twentieth century.

More intriguing at the time was the 'black body' problem, some smart person figured out you could tell the temperature of an object by the spectra of the radiation it gave off. Then some other smart person asked why. The big question being, why doesn't all the energy just cascade up to a higher frequency.(Sorry I learned my physics from cereal boxes.)

 

[Brian]

Thanks for the link Luke and the reply DD.
The more I learn about relativity, the more I realise why it's treated as such a big deal.
One little equation and among everything else he gave astrophysicists and astronomers a huge missing piece of the puzzle. Never occured to me before.

 

[garys_2k]

http://www.curtin.edu.au/curtin/dept/phys-sci/sun/energyhs.htm

From that link:

It was calculated however that every 100 years, meterorites totalling the mass of the Earth would have to fall into the Sun. Such a change in mass would change the period of our revolution around the Sun and this is not the case.

WOW! So they figured that if the mass of the earth was added to the sun every century we'd see an orbital change? Man, I guess they were off on some other things besides fuel, weren't they?

Maybe I'm wrong, but I'd guess that much mass added to the sun wouldn't be large enough to make a significant difference. Likewise, the mass loss from fusion must add up after a few million years too, but does that cause an orbit shift? What about the solar wind ions? Those must add up.

 

[wollery]

Kelvin figured out that it couldn't be just gravitational friction (okay maybe it wasn't Kelvin). It didn't take long for people to eliminate chemical reaction.

That was just one of many problems solved in the twentieth century.

More intriguing at the time was the 'black body' problem, some smart person figured out you could tell the temperature of an object by the spectra of the radiation it gave off. Then some other smart person asked why. The big question being, why doesn't all the energy just cascade up to a higher frequency.(Sorry I learned my physics from cereal boxes.)

This was actually the question that kicked off quantum physics. If you do the calculations in classical physics the energy does cascade to higher frequencies (at the limit of the calculation you get infinite energy produced at zero wavelength). Planck came up with the answer - energy comes in little packets or quanta. once they had that it was just a matter of statistics to show that any body in thermal equilibrium (or in the case of stars local thermal equilibrium) will emit a blackbody curve.