Newton's gravitational constant.

[swansont]

all things in consideration +/- 5 *10^26 kg isn't all that accurate. thats a hundred earths either way.

 

But it was 5 x 10^23, not 10^26. A tenth of an earth.

[insane_alien]

i was reffering to th figure given by dstebbins

 

1.9891 x 10^30 kg

[dstebbins]

Express "tons and tons" (actually ~4e9 kg) as a fraction of 10^30 kg and you'll see.

 

Done. I know see that, if the time the measurement was taken were placed at zero years, with all time beforehand being negative years, the sun would burn out in the year 2.19 x 10^25.

 

But then why do we say the Sun only has a few billion years to go?

[insane_alien]

because the sun will never convert all of its mass to energy. it blows up well before then.

 

oh and swansont, i get where you were coming from there. i had a bit of a brain fart there.

[dstebbins]

because the sun will never convert all of its mass to energy. it blows up well before then.

 

oh and swansont, i get where you were coming from there. i had a bit of a brain fart there.

 

oh, such as when a star turns into a black hole by imploding?

[insane_alien]

or just going super nova. or if its a red dwarf it could just turn into a black dwarf in a few trillion years.

[swansont]

oh and swansont, i get where you were coming from there. i had a bit of a brain fart there.

 

Happens to all of us.

[swansont]

The conversion of Hydrogen to Helium changes the mass by less than a percent, and the sun won't get past converting to Carbon (with similar scale reduction in mass). After that it just isn't hot enough (which is dependent on the mass) to continue fusing, and the fusion only involves the material in the core of the star. That's why the sun has a predicted lifetime of about 10 billion years, with ~half yet to go.

[dstebbins]

The conversion of Hydrogen to Helium changes the mass by less than a percent, and the sun won't get past converting to Carbon (with similar scale reduction in mass). After that it just isn't hot enough (which is dependent on the mass) to continue fusing, and the fusion only involves the material in the core of the star. That's why the sun has a predicted lifetime of about 10 billion years, with ~half yet to go.

 

But shouldn't the mass of the sun be decreasing due to e-mc^2? According to that theory, the energy you get e from mass m is qual to the product of the mass and the square of the speed of light in a vacuum, meaning that a single kilogram of anything fused together creates 9.00 x 10^16 J of energy. Shouldn't you be considering that in your explaination?

 

On a side note, that brings up another problem. I'll make another thread about it to keep this thread's clutter down.

[insane_alien]

he did. the mass does change according to E=mc^2 its just that not enough of the mass reacts before the star rips itself appart and stops reacting.

[Spyman]

Stars converts matter to energy by nuclear fusion generated by the gravitational pressure. The nuclear reactions in the core determines how much mass is converted.

 

You can use E=mc² to calculate how much energy the Sun radiates out in space or to calculate how much mass is converted by estimating how much energy is radiated.

 

The Sun is thought to be about 4.57 billion years and in 4-5 billion years it is supposed to enter a red giant phase when Helium fusion begins.

 

The most important fusion process in nature is that which powers the stars. The net result is the fusion of four protons into one alpha particle, with the release of two positrons, two neutrinos (which changes two of the protons into neutrons), and energy, but several individual reactions are involved, depending on the mass of the star. For stars the size of the sun or smaller, the proton-proton chain dominates. In heavier stars, the CNO cycle is more important. Both types of processes are responsible for the creation of new elements as part of stellar nucleosynthesis.

http://en.wikipedia.org/wiki/Nuclear_fusion

 

The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than 4 million tonnes of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. The Sun will spend a total of approximately 10 billion years as a main sequence star.

http://en.wikipedia.org/wiki/Sun

 

After millions to billions of years, depending on the initial mass of the star, the continuous fusion of hydrogen into helium will cause a build-up of helium in the core. Larger and hotter stars produce helium more rapidly than cooler and less massive ones. The accumulation of helium produces a gradual increase in the rate of fusion, because the higher density of helium (compared to hydrogen) at a given temperature causes the core to contract, which increases its gravitational self-compression, thus requiring the core to achieve a higher temperature to remain at steady state than when the helium concentration was lower.

 

Eventually, hydrogen is exhausted in the core, and without the outward pressure generated by the fusion of hydrogen to counteract the force of gravity, the core contracts until either electron degeneracy becomes sufficient to oppose gravity, or the core becomes hot enough (around 100 megakelvins) for helium fusion to begin. Which of these happens first depends upon the star's mass.

http://en.wikipedia.org/wiki/Stellar_evolution

[swansont]

The mass difference between four protons and a helium nucleus is only a small fraction of the total.