Science In Real Life: The Sun
Let's talk about the sun, or as one of my paler friends calls it, the Oppressive Daystar. This series is about the science of everyday things, and it's tough to get more quotidian than the thing that makes the days itself. There is, of course, entirely too much physics here to cover it all in this essay, so I'll be focusing on the general life history of the sun and the mechanism by which it generates all that light.
A long time ago, in a galaxy very very close to here, a gaseous nebula at the unfashionable end of the Western spiral arm of the galaxy begins to condense. Gravity is unrelenting and universal, and slowly the mass of the nebula clumps together into a spinning gaseous disk with a spherical center. We will leave the disk aside from now, because the spherical center now begins to compress even more.
The pressure inside the ball of gas builds. Slowly at first, then faster as it shrinks under its own weight. It is composed primarily of hydrogen atoms, with traces of a few other elements like helium and some metals. As the pressure increases, the atoms collide with each other more frequently and more energetically, faster and faster, harder and harder, until ...
BANG! What finally happened is that the hydrogen atoms began to collide with enough energy that they overcame the repulsive force between them (two positive charges repel each other) and became bound together by a different force, called the strong force (very creative with names, us physicists). Have you ever wondered what holds protons and neutrons together in a tight little nucleus? It's the strong force, a hundred times stronger than any electrostatic attraction or repulsion, but only operating over a range equal to the size of a proton.
Let me break here to provide a little bit of scale, since I made a sharp left into atomic physics without warning you guys to put on your seatbelts first. Your average ordinary atom is 99% empty space. Imagine enlarging an atom until it's the size of a football stadium. Then the nucleus would be a single solitary pea on the center of the 50 yard line, and the very closest electron would be a very invisible, very dedicated fan sitting in the highest nosebleed seats. So when I talk about atoms colliding, I'm really talking about their nuclei colliding, because the electrons are just too ephemeral.
Now, let's put some scale on these forces. Imagine the lower 48 states of the USA are completely empty, devoid of life except you and your arch-enemy. Neither of you can leave the country, so you both drive around at random. But there's a restraining order that prevents either of you from driving into the same state as the other - this is like the electrostatic repulsion. But I turn up the energy, you both drive faster and faster until suddenly you've violated the order without realizing it and you drive past each other on the same road, destined from that moment on to drive within sight of one another. That's the strong force.
So. What happens when two hydrogen atoms fuse? Those of you familiar with the periodic table of the elements will know that an atom that has two protons is helium. It's actually a more complicated process than that, but the upshot is that hydrogen goes in, helium and energy come out. That energy is emitted as photons, and it eventually makes its way from the very core of the sun, where the magic happens, out to the surface. Because the sun is so unbelievably dense, this part actually takes about 300,000 years. Like a maserati stuck in traffic, it doesn't go nearly as fast as it could.
Once it does reach the surface, it travels outwards in all directions. Some of it, after zipping along through space for about 8.5 minutes, has the good fortune to run into a bluegreen mudball called Earth, where it powers almost every biological process on the planet, and a few non-biological ones for good measure.
Now, this is all well and good, but about five billion years from now the sun is going to run out of hydrogen. There will only be helium (as well as those other traces). As it turns out, the energy coming from the fusion of hydrogen is the only thing stopping the sun from compressing even further under its own weight. When the hydrogen runs out, Samson gets a haircut and the whole structure will come toppling down, until BANG! again, because it'll be hot enough for the helium atoms to fuse into carbon. In fact, it'll be so hot that the sun not only won't be shrinking, it'll be expanding. It will expand all the way out to Earth's orbit and beyond. We will be a baked Earth, hold the bacon bits.
But you don't need to concern yourself with that, because the Sun is steadily increasing its output all the while, and in about one billion years it'll be too hot for any water to remain on the surface of our planet. We'll be a fried Earth, hold the mayo. And before that, all the carbon dioxide will be forced down onto the ocean floor as rains increase. Plants will suffocate and we'll all die.
Have a bright and sunny day!
Extra Credit: Watch this video.
A long time ago, in a galaxy very very close to here, a gaseous nebula at the unfashionable end of the Western spiral arm of the galaxy begins to condense. Gravity is unrelenting and universal, and slowly the mass of the nebula clumps together into a spinning gaseous disk with a spherical center. We will leave the disk aside from now, because the spherical center now begins to compress even more.
The pressure inside the ball of gas builds. Slowly at first, then faster as it shrinks under its own weight. It is composed primarily of hydrogen atoms, with traces of a few other elements like helium and some metals. As the pressure increases, the atoms collide with each other more frequently and more energetically, faster and faster, harder and harder, until ...
BANG! What finally happened is that the hydrogen atoms began to collide with enough energy that they overcame the repulsive force between them (two positive charges repel each other) and became bound together by a different force, called the strong force (very creative with names, us physicists). Have you ever wondered what holds protons and neutrons together in a tight little nucleus? It's the strong force, a hundred times stronger than any electrostatic attraction or repulsion, but only operating over a range equal to the size of a proton.
Let me break here to provide a little bit of scale, since I made a sharp left into atomic physics without warning you guys to put on your seatbelts first. Your average ordinary atom is 99% empty space. Imagine enlarging an atom until it's the size of a football stadium. Then the nucleus would be a single solitary pea on the center of the 50 yard line, and the very closest electron would be a very invisible, very dedicated fan sitting in the highest nosebleed seats. So when I talk about atoms colliding, I'm really talking about their nuclei colliding, because the electrons are just too ephemeral.
Now, let's put some scale on these forces. Imagine the lower 48 states of the USA are completely empty, devoid of life except you and your arch-enemy. Neither of you can leave the country, so you both drive around at random. But there's a restraining order that prevents either of you from driving into the same state as the other - this is like the electrostatic repulsion. But I turn up the energy, you both drive faster and faster until suddenly you've violated the order without realizing it and you drive past each other on the same road, destined from that moment on to drive within sight of one another. That's the strong force.
So. What happens when two hydrogen atoms fuse? Those of you familiar with the periodic table of the elements will know that an atom that has two protons is helium. It's actually a more complicated process than that, but the upshot is that hydrogen goes in, helium and energy come out. That energy is emitted as photons, and it eventually makes its way from the very core of the sun, where the magic happens, out to the surface. Because the sun is so unbelievably dense, this part actually takes about 300,000 years. Like a maserati stuck in traffic, it doesn't go nearly as fast as it could.
Once it does reach the surface, it travels outwards in all directions. Some of it, after zipping along through space for about 8.5 minutes, has the good fortune to run into a bluegreen mudball called Earth, where it powers almost every biological process on the planet, and a few non-biological ones for good measure.
Now, this is all well and good, but about five billion years from now the sun is going to run out of hydrogen. There will only be helium (as well as those other traces). As it turns out, the energy coming from the fusion of hydrogen is the only thing stopping the sun from compressing even further under its own weight. When the hydrogen runs out, Samson gets a haircut and the whole structure will come toppling down, until BANG! again, because it'll be hot enough for the helium atoms to fuse into carbon. In fact, it'll be so hot that the sun not only won't be shrinking, it'll be expanding. It will expand all the way out to Earth's orbit and beyond. We will be a baked Earth, hold the bacon bits.
But you don't need to concern yourself with that, because the Sun is steadily increasing its output all the while, and in about one billion years it'll be too hot for any water to remain on the surface of our planet. We'll be a fried Earth, hold the mayo. And before that, all the carbon dioxide will be forced down onto the ocean floor as rains increase. Plants will suffocate and we'll all die.
Have a bright and sunny day!
Extra Credit: Watch this video.