/sci/ - Science & Math

>implying there's fire on the Sun
>implying I won't sage

>>3123027
>Why is the sun on fire?
It's not. The light of the sun does not result from an oxygen chemical reaction.

sorry worded that wrong why is it hot?

>>3123038
Nuclear reactions. Really, see wiki.

why is the universe so cold?

what happens when you collide a sun made of ice and a regular sun?

i was just curious because i read a post online that said mass amounts of gravity created mass amounts of pressure.and large amounts of pressure create equal heat.

>>3123054
Because space is a vacuum

>>3123060
Kind of. Mass amounts of pressure acting on fusionable material creates mass amounts of heat and light.

>>3123060
Well, that large amount of pressure actually causing Hydrogen atoms to be crushed together into a Helium atom, releasing a lot of energy in the middle.

>>3123064
why is space a vacuum?

>>3123077
It's not.

so what if something was the same amount of mass but was not a fusionable material

>>3123038
>>3123050
>>3123050

noooooooooooooooo.
i hate seeing that misconception.

GRAVITY powers the sun. nuclear reactions COOL the sun.
the sun is very massive, as a result, it has a very strong gravitational pull, especially near the center. thus, particles trying to leave the sun are constantly pulled (and accelerated) back in.
as you know, temperature is a measure of kinetic energy. so particles that are moving faster are hotter. thus the sun is extremely hot.

nuclear reactions are taking energy AWAY from the sun. consider a particle revolving around inside the sun. a nuclear reaction pushes this particle out, giving it a larger radius of revolution. in order to conserve energy, an increase in radius results in a DECREASE in kinetic energy. then the sun's very strong gravity pulls it back in and reduces the radius (thus INCREASING the kinetic energy) and makes the sun hotter!

i still remember the day we learned this in astronomy, it's a very cool result

>>3123089
White dwarf -> brown dwarf -> black dwarf, or neutron star, or black hole.

>>3123064
>>3123087

>>3123098
Very cool to know. Still, that's not the answer to his intended question. Without the nuclear reactions, the sun may be very hot, but it would also be very dark, much less bright than it currently is, like a brown/black dwarf, neutron star, or black hole.

>>3123098
Yes, stars radiate heat (among other things), but nuclear fusion is what produces it. While what you said is completely correct, it only means that stars are self-correcting systems (decrease in fusion causes it to contract, this increases pressure and temperature in the core thus making fusion faster which then expands the star a little and so on).
PS. I'm not correcting you, just adding more info.

>>3123125
What this anon said, because I'm apparently retarding it up.

>>3123098
>>3123098
(continuing)

think of it like this:
nuclear reactions are mediating the sun, making sure it doesn't collapse onto itself.

think about it -- when a star runs out of fuel (fuse-able hydrogen), it's core collapses (contracts) and gets much HOTTER! this is because the nuclear reactions aren't there to keep pushing it out and robbing energy from it.

it's weird to think of a nuclear explosion as something that "cools" the sun, but this is how it really works!


>>3123125
>>3123106

actually, this is another lesser-known, but just as important misconception.
nuclear reactions DO NOT produce the heat that powers the sun. it seems logical to think that the sun radiates heat/energy because the nuclear reactions throw it out, but this is not the case.

like we said earlier, the sun is hot because of GRAVITY.

in physics (and it's also taught in astronomy classes) there is a law known as the Stefan-Boltzman Law. it is the following:

P = (sigma) T^4

where P is power output, sigma is the Stefan-Boltzmann constant, and T is absolute temperature.

this law says that objects radiate heat (energy) PURELY AND SOLELY AS A CONSEQUENCE OF THE OBJECT BEING HOT.
THIS is the heat that the sun radiates. and it is because the sun is hot.

and why is the sun hot? gravity!


the only purpose of nuclear reactions is to moderate the sun and to fuse atoms which will eventually become us!

Sun is a giant ball of plasma... to simplify.

>>3123157
Now that I read the thread, anon asked why the sun is hot, not why it radiates EM waves in general, making my post irrelevant.

>>3123173
>>3123173

O_o nigga, why the fuck are you posting as if you're the one who wrote that?

i was clearing up misconceptions presented by others and hopefully trying to help OP out a little too.

fuck.

if you don't like my post say so, don't pretend to be me

>>3123180
Ehm, I'm>>3123125
Read it and you'll see I'm not pretending to be you.

>>3123190

oh shit my bad.
for some reason, the way i read made it seem that way to me.

sorry bout that

>>3123157
You seem to be very confused still. While I agree with everyone you wrote, you seem to not know that without the energy supplied from the nuclear reactions, the sun would "quickly" radiate away all of its heat energy through black body radiation and such. Without the nuclear furnace, the sun would have stopped being hot and glowing quite a long time ago. When the sun runs out of nuclear fuel, exactly that will happen. It will (eventually) start cooling due to lack of input energy and loss of energy through radiation.

ok then follow up why is all that fusionable material on the sun?

>>3123198
Our sun formed out of a huge gas cloud of molecular hydrogen, and some other trace elements around ~5 billion years ago. The planets also coalesced out of this gas cloud, but some didn't have enough gas/gravity when the sun ignited so then the hydrogen and helium gas clouds largely flew away.
The sun has a LOT of hydrogen.

>>3123195
>>3123195

i don't know that i agree with you there.
the nuclear reactions aren't pumping *new* energy into the sun. The sun is a closed system, it doesn't gain energy from anything, it's only losing energy. none of that energy is being replenished.

let's call the total energy stored in the sun at some (arbitrary) reference time, E0. then it is radiating away energy at a rate, P (it's power), proportional to it's temperature (let's just assume it's linear over some small time that we will measure - ie the temperature of the sun doesn't go down very much in this time):

then the total energy of the sun as a function of time, E(t), is:

E(t) = E0 - P*t

nothing is coming in to replenish this energy to the sun so that E(t) stays constant. in fact, if we calculate the mass that the sun is losing (from the energy that it's radiating), the sun is losing ~4,000,000 tons per second! and this has been going on for... WEEKS!

so, it IS radiating away a lot of energy (and mass).


the only part that nuclear fusion plays is keeping the sun cool enough so that it doesn't radiate as much (from P = sigma * T^4).
is this all you were trying to say?
i got the impression that you were saying that nuclear reactions ADD energy to the sun, which in fact, they don't

Correct. Because it is made of lava.

THIS sun is made of ice.

What would happen if a sun made of lava collided with a sun made of ice?

Experiment #1...