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Earth in the sun's orbit
Several questions. Hope somebody here can explain.
Each second the sun burns 10 million tonnes of hydrogen. The sun is at the same time getting gradually denser due to nuclear fusion in its core. What is the overall effect of these two factors over time on the sun's gravitational pull: does it increase or decrease? Does it vary according to the sun's position on the main sequence? Is this different for non-main sequence stars? I seem to remember reading that over time the sun's force of gravity increases. The earth is at the same time accreting débris from space - from the solar wind and from solar system residue. What is the effect of this - and the above changes in the sun's gravitational field - on the earth's orbit? There are also tidal forces on the earth (and to a much less extent on the sun) which tend to slow its rotation. Does this translate into angular momentum in the earth's orbit? In how much time will the earth have one face permanently pointing to the sun, with the other looking away into permanent night? Will this be a problem before the increased heat of the sun turns the earth into another Venus? That's enough questions! |
#2
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Earth in the sun's orbit
"Carusus" wrote in message ... Several questions. Hope somebody here can explain. Each second the sun burns 10 million tonnes of hydrogen. The sun is at the same time getting gradually denser due to nuclear fusion in its core. What is the overall effect of these two factors over time on the sun's gravitational pull: does it increase or decrease? Does it vary according to the sun's position on the main sequence? Is this different for non-main sequence stars? All stars emit vast amounts of energy. From the famous equation e=mc^2 (i.e. the energy emitted actually has a mass), it follows that all stars are losing vast amounts of mass. For the Sun, this is 4.25 million tonnes per second. I'd imagine a pretty vast amount of mass is lost from solar wind as well. The mass gain from comets/rocks crashing into the Sun is many times less than this, so overall, the Sun is losing mass. This basically means that the Sun's gravitational field strength is decreasing. The earth is at the same time accreting débris from space - from the solar wind and from solar system residue. What is the effect of this - and the above changes in the sun's gravitational field - on the earth's orbit? The Earth's orbit should increase in radius - mainly due to what I've said above. There are also tidal forces on the earth (and to a much less extent on the sun) which tend to slow its rotation. Does this translate into angular momentum in the earth's orbit? In how much time will the earth have one face permanently pointing to the sun Initially, the Earth will become tidally locked with the Moon, but this will not happen until the Sun has finished it's red giant phase. The tidal forces from the white dwarf Sun - perhaps having only around half of its current mass will mean that the Moon would gradually spiral inwards and get broken up as it nears the Earth. Not until this happens would there be an opportuni ty for the Earth to get tidally locked with the Sun. I think we're talking hundreds of billions of years, if not trillions of years for this to happen. , with the other looking away into permanent night? Will this be a problem before the increased heat of the sun turns the earth into another Venus? No, it's expected that Earth will begin to have a runaway greenhouse effect in only a billion years or so, Ric |
#3
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Earth in the sun's orbit
"Carusus" wrote in message
... Several questions. Hope somebody here can explain. Each second the sun burns 10 million tonnes of hydrogen. The sun is at the same time getting gradually denser due to nuclear fusion in its core. What is the overall effect of these two factors over time on the sun's gravitational pull: does it increase or decrease? Does it vary according to the sun's position on the main sequence? Is this different for non-main sequence stars? I seem to remember reading that over time the sun's force of gravity increases. The density of the Sun will not affect its gravitational pull on the planets (provided that its contents remain inside their orbits). Only a change in mass will do that. The Solar Constant at the Earth's distance is about 1370W/m^2, so taking the surface area of a spherical surface at the same radius, we find that the total energy flux is 1370W/m^2 * 4*pi*(1.496x10^8km)^2 = 3.85x10^26W or 3.85x10^26 Joules/sec Using E = m*c^2 and solving for mass, we find that the Sun loses about 4.3x10^9 kg/sec. Compare this with the total mass of the sun, some 2*10^30 kg. It's practically negligible. The time for the Sun to lose 1% of its mass at this rate is about 150 billion years. So there's no reason to worry about it. The Sun will have been long past its red giant stage by then. The earth is at the same time accreting débris from space - from the solar wind and from solar system residue. What is the effect of this - and the above changes in the sun's gravitational field - on the earth's orbit? As shown above, the Sun's gravitational field will not change perceptibly, and the Earth, being so much less massive than the Sun, will not have its orbit affected by any change in its own mass. Remember, all bodies fall at the same rate in a gravitational field due to the equivalence principle. The purtubations caused by the other planets, most notably Jupiter, have a much greater long term effect than any mass changes of Sun or Earth. There are also tidal forces on the earth (and to a much less extent on the sun) which tend to slow its rotation. Does this translate into angular momentum in the earth's orbit? In how much time will the earth have one face permanently pointing to the sun, with the other looking away into permanent night? Will this be a problem before the increased heat of the sun turns the earth into another Venus? The Earth tides due to the Sun will act to move anglular momentum from the Earth's rotation to its orbit around the Sun. But the time scale for any significant change is vast, certainly longer than the Sun's lifetime. |
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Earth in the sun's orbit
What a relief! I thought it was 500 million years or so. Dang! why
did I buy the big air conditioner. Richard Bullock wrote: "Carusus" wrote in message ... Several questions. Hope somebody here can explain. Each second the sun burns 10 million tonnes of hydrogen. The sun is at the same time getting gradually denser due to nuclear fusion in its core. What is the overall effect of these two factors over time on the sun's gravitational pull: does it increase or decrease? Does it vary according to the sun's position on the main sequence? Is this different for non-main sequence stars? All stars emit vast amounts of energy. From the famous equation e=mc^2 (i.e. the energy emitted actually has a mass), it follows that all stars are losing vast amounts of mass. For the Sun, this is 4.25 million tonnes per second. I'd imagine a pretty vast amount of mass is lost from solar wind as well. The mass gain from comets/rocks crashing into the Sun is many times less than this, so overall, the Sun is losing mass. This basically means that the Sun's gravitational field strength is decreasing. The earth is at the same time accreting débris from space - from the solar wind and from solar system residue. What is the effect of this - and the above changes in the sun's gravitational field - on the earth's orbit? The Earth's orbit should increase in radius - mainly due to what I've said above. There are also tidal forces on the earth (and to a much less extent on the sun) which tend to slow its rotation. Does this translate into angular momentum in the earth's orbit? In how much time will the earth have one face permanently pointing to the sun Initially, the Earth will become tidally locked with the Moon, but this will not happen until the Sun has finished it's red giant phase. The tidal forces from the white dwarf Sun - perhaps having only around half of its current mass will mean that the Moon would gradually spiral inwards and get broken up as it nears the Earth. Not until this happens would there be an opportuni ty for the Earth to get tidally locked with the Sun. I think we're talking hundreds of billions of years, if not trillions of years for this to happen. , with the other looking away into permanent night? Will this be a problem before the increased heat of the sun turns the earth into another Venus? No, it's expected that Earth will begin to have a runaway greenhouse effect in only a billion years or so, Ric |
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Earth in the sun's orbit
In message , Richard
Bullock writes "Carusus" wrote in message ... Several questions. Hope somebody here can explain. Each second the sun burns 10 million tonnes of hydrogen. The sun is at the same time getting gradually denser due to nuclear fusion in its core. What is the overall effect of these two factors over time on the sun's gravitational pull: does it increase or decrease? Does it vary according to the sun's position on the main sequence? Is this different for non-main sequence stars? All stars emit vast amounts of energy. From the famous equation e=mc^2 (i.e. the energy emitted actually has a mass), it follows that all stars are losing vast amounts of mass. For the Sun, this is 4.25 million tonnes per second. I'd imagine a pretty vast amount of mass is lost from solar wind as well. The mass gain from comets/rocks crashing into the Sun is many times less than this, so overall, the Sun is losing mass. This basically means that the Sun's gravitational field strength is decreasing. Over 4.5 billion years you're talking about 4500 x 4.25 x 31 = 600 thousand million million million tons lost by fusion, roughly. Call it 10^24 tons. But the Sun's mass is 2 x 10^27 tons, so you're losing less than one part in 2000. The rate goes up drastically at the end of the Sun's life, and it's been argued the Earth may survive the red giant phase. And going back to "Carusus" post, non-main-sequence stars - including the Sun at the end of its life, as well as a lot of giant stars - lose a lot of mass, Several percent, at least. -- "Roads in space for rockets to travel....four-dimensional roads, curving with relativity" Mail to jsilverlight AT merseia.fsnet.co.uk is welcome. Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk |
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Earth in the sun's orbit
Carusus wrote:
Many thanks for your prompt answer and clear explanations. However, your first answer does not seem to take account of the increasing density of the sun, which presumably affects its gravitational pull. As Greg points out (it appears his posting arrived just after you sent the above) the density or distribution of mass in a body has no effect on the gravitational force it produces from a distance: only the total mass counts, and it may be treated as if it were all located at the body's centre of mass. So if the sun's density is increasing this implies it will contract more than one would expect from the loss of mass alone, but the gravitational force experienced by the earth will continue to be a simple function of the sun's remaining mass and the distance to its centre. --Odysseus |
#7
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Earth in the sun's orbit
http://zebu.uoregon.edu/~soper/Sun/mass.html
gives 2x10^30 as the mass of the sun. Is this correct? It doesn't change much, other than to reinforce the idea that the percentage is small. Jonathan Silverlight wrote: In message , Richard Bullock writes "Carusus" wrote in message ... Several questions. Hope somebody here can explain. Each second the sun burns 10 million tonnes of hydrogen. The sun is at the same time getting gradually denser due to nuclear fusion in its core. What is the overall effect of these two factors over time on the sun's gravitational pull: does it increase or decrease? Does it vary according to the sun's position on the main sequence? Is this different for non-main sequence stars? All stars emit vast amounts of energy. From the famous equation e=mc^2 (i.e. the energy emitted actually has a mass), it follows that all stars are losing vast amounts of mass. For the Sun, this is 4.25 million tonnes per second. I'd imagine a pretty vast amount of mass is lost from solar wind as well. The mass gain from comets/rocks crashing into the Sun is many times less than this, so overall, the Sun is losing mass. This basically means that the Sun's gravitational field strength is decreasing. Over 4.5 billion years you're talking about 4500 x 4.25 x 31 = 600 thousand million million million tons lost by fusion, roughly. Call it 10^24 tons. But the Sun's mass is 2 x 10^27 tons, so you're losing less than one part in 2000. The rate goes up drastically at the end of the Sun's life, and it's been argued the Earth may survive the red giant phase. And going back to "Carusus" post, non-main-sequence stars - including the Sun at the end of its life, as well as a lot of giant stars - lose a lot of mass, Several percent, at least. |
#8
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Earth in the sun's orbit
"Carusus" wrote...
in message ... http://zebu.uoregon.edu/~soper/Sun/mass.html gives 2x10^30 as the mass of the sun. Is this correct? Just be careful, Carusus... don't make the mistake *i* did (and i caught before posting). Jonathan's units of measurement are "tons," and Greg's units are in "kilograms." So the mass of the Sun is... 2 x 10^30 kilograms which is about equal to... 2 x 10^27 tons It doesn't change much, other than to reinforce the idea that the percentage is small. If one were using the same units, the difference would be a factor of a thousand (1,000). That might be significant enough to alter our views about the Sun's age, term of life, death and other qualities. And it might give us good questions to ponder... If the Sun's mass were 1,000 times less (or 1,000 times more), then what would its life expectancy change to? Would it "die" differently? Would it now be a different color to our eyes? If 1,000 times more mass, would it then have enough mass to go nova? supernova? Studying questions like these might give us more precision as to the ages of other celestial objects we observe. happy days and... starry starry nights! -- Life without love is A lamp without oil, Love without prejudice A world without soil, Tool without toil. Paine Ellsworth |
#9
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Earth in the sun's orbit
"Carusus" wrote in message
... http://zebu.uoregon.edu/~soper/Sun/mass.html gives 2x10^30 as the mass of the sun. Is this correct? Not without specifying the units. In this case, kg would be the units, and the value 2x10^30kg would be a reasonable approximation to the mass of the Sun. I've seen a figure of 1.989x10^30kg quoted. |
#10
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Earth in the sun's orbit
In message ,
Painius writes And it might give us good questions to ponder... If the Sun's mass were 1,000 times less (or 1,000 times more), then what would its life expectancy change to? Would it "die" differently? Would it now be a different color to our eyes? If 1,000 times more mass, would it then have enough mass to go nova? supernova? Well, if current theories are right a star 1000x the mass of our sun is unstable and explodes, while 1/1000 of the mass of the sun is almost exactly the mass of Jupiter, so it isn't a star any more. -- "Roads in space for rockets to travel....four-dimensional roads, curving with relativity" Mail to jsilverlight AT merseia.fsnet.co.uk is welcome. Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk |
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