Look Up

by Mitchell Tester, College Student

““FAT OLD SUN””

The sun is a means for all living beings to exist, sitting at the center of our own solar system, 93 million miles from us here on Earth. Taking a trip around the Sun would take you 2.7 million miles, or 1,889 days, at a steady 60 miles per hour. On the contrary, a trip around Earth would take you only 17 days.

Although the Sun trumps the Earth in terms of size, the Sun is surprisingly quite small when compared to some stars of neighboring solar systems and galaxies. In fact, the biggest star in the known universe, UY Scuti, has a radius 1,700 times larger than the Sun. Therefore, the circumference of UY Scuti sits at a staggering 4,619,398,440 billion miles. A nice leisurely journey around UY Scuti would take 3 million days, or nearly 9,000 years, at 60 miles per hour.

Since driving on a star is impossible for many reasons, let’s instead say that you wanted to fly around UY Scuti in a spacecraft with speeds similar to the Apollo 11 mission, fitted with protection against the radiation and immense heat and with a breakneck speed of 24,790 miles per hour. Despite our more than impressive imaginary craft, it would still take us 21 years to fly around the star at a steady pace. This means, this big star is large enough to fit 6 quadrillion Earths inside of it, unlike the meager 1.3 million Earths that can fit inside our own star, the Sun.

The Sun started its life at the center of a solar nebula, basically an interstellar dust cloud, some 4 billion years ago. Interestingly enough, scientists have strongly theorized that our own planets and everything else in our solar system were formed in this same cloud. Disturbances by way of neighboring clouds, exploding stars, and other celestial occurrences are ways for the dust in these clouds to clump together, in addition to the force of their own gravity, growing larger and larger, until after millions of years, a protostar is formed from the core of that solar nebula. And for another 100,000 to 10 million years, it continues to collect mass until it finally stops collapsing in on itself. The time frame of a star’s life and its stages are heavily dependent on the mass of the star, so stay tuned for next month when I talk about the birth and death of stars in part two of “Fat Old Sun.”

For our protostar, eventually the immense pressure, extremely high temperatures, and accretion of material causes hydrogen to fuse into helium by way of nuclear fusion. When the atomic nuclei, hydrogen, starts to bond into a single heavier one, helium, the star is then born. At 25 million degrees Fahrenheit, it burns 600 million tons of hydrogen into helium every second, the equivalent of 10 billion hydrogen bombs.

The pressure that the star gives outward through its nuclear fusion is great enough that it is equal to the pressure inward, inward pressure being the collapsing of material because of gravity. This balancing act is something called hydrostatic equilibrium. One force holds the Sun together, making it spherical, while the other keeps it from collapsing in on itself. Like most things in life, balance is vital.

The nuclear fusion that is occurring in our Sun is occurring in the core, where the pressure and the temperature are so high that the nuclei can be fused together rather than be repelled from one another (which they naturally do).

The energy that is created by the heart of the Sun is called photons, packets of energy that move in waves. The packets of energy, photons, are created by the excitement of an electron and its journey back to a stable state (they like to be stable), that energy needs to go somewhere, so it goes outward. So, the photons’ journey then begins, saying goodbye to their atomic friend, they then move toward the radiative layer of the Sun, to be absorbed and emitted many times throughout their journey.

Inside the radiative layer, the energy created in the core is carried by photons outward, through thermal radiation, which occurs from the high temperatures that cause kinetic energy (energy that is created by movement) of random movements of atoms and molecules in the matter of the Sun. This is at the (literal) core of what heats us here on Earth.

As energy is carried through the radiative layer, it then moves to the convection layer of the Sun, still being absorbed and emitted over and over. Heat rises, which means the Sun, in a figurative sense, lives by the same rules as heating your house does. Due to heat rising, it means the coolness sinks to make way for the heat. This rotation in temperature causes convection—heated gas rises and the denser cooler gas sinks.

The photons continue their journey outward through the hot gas, making their way into the photosphere, which is the visible surface of the Sun. This photosphere is the coolest layer, although still reaching temps of 10,000 degrees Fahrenheit. If you look at an image of the Sun, you will notice a granulation texture seen on the surface. That texture is the before-mentioned clumps of hot gas rising, and the darker (in comparison observed as black) clumps of cool gas sinking inward. When I say gas, I am specifically talking about a superheated gas called plasma, often referred to as the fourth state of matter. Plasma is what happens when extreme conditions are met, superheated matter (in this case, gas) is stripped of its electron(s), electrically charging it (referred to as becoming ionized) and turning it into plasma.

The photons move onward, continuing their journey towards Earth, then reaching the Sun’s atmosphere’s first layer, the inner layer, the chromosphere, a thin layer of red-colored plasma (chromo meaning color). The chromosphere is usually hidden from our view, although it can be seen by special satellite telescopes and even during a solar eclipse. While the photons continue to rise or move outward, they reach the corona, the outermost layer of the Sun. The corona is the least dense layer of the Sun, in addition to carrying the least amount of energy. Despite this, it is extremely hot, upwards of 2 million degrees Fahrenheit, even hotter than the chromosphere. There are many theories as to why the outer layer is hotter, although there is no definitive answer yet.

Photons, moving outward in all directions, passing through the outer reaches of the Sun’s corona, having been emitted and absorbed countless times throughout the Sun’s layers, are now in space, traveling away from the Sun. Interestingly enough, the distance that photons can reach is not finite, continuing on forever as long as there is no interruption, which can occur by way of a planet, black hole, or anything else that absorbs light. This is how we see the light of stars that are trillions and trillions of miles away. Our photons, after completing their journey through the Sun, are then carried through the vacuum of space, by electromagnetic radiation at the speed of light, to our home, the Earth. It actually takes light, or photons, roughly 8 minutes to travel the 93,000,000 miles to Earth. While from the core to the corona, the journey can take upward of around 10,000 to 170,000 years.

The photons, nearing at the end of their journey, are now coming close to contact with Earth’s atmosphere. Before telling you what happens to our photon friends when contact is made with our Earth’s atmosphere, I must explain one thing: Photons are made up of everything in the electromagnetic spectrum, which includes all the colors of visible light. As you may know, all those colors together make white light. Think of Isaac Newton and his experiment of letting light travel through a prism—white light in, all the colors of the rainbow out.

Have you ever found yourself looking up and wondering why the sky is blue? Photons do indeed play a role in that, although photons alone are not the reason our sky is blue. Our sky is blue due to nitrogen and oxygen making up 99 percent of our atmosphere, therefore, effectively scattering the blue and violet light from the photons, while the other colors of the white light spectra make their way down to Earth, mostly unphased. This is also why the Sun appears a yellowish orange to us here on Earth; while, if you were in space, the Sun would be white because it is white light. Although here on Earth, due to nitrogen and oxygen effectively scattering blue light, the lack of blue light (because it is being scattered in the atmosphere) leaves the Sun looking a yellowish orange. If you are wondering why the Sun appears red when it is close to the horizon, that is due to the light going through more of the atmosphere, in return scattering more blue light than normal, leaving the Sun reddish orange rather than yellow.

So, now you know, as you walk outside in the morning to see that (technically white) fat old sun rising, feeling the warmth on your face, the particles that gave way to this feeling took 10,000 to 170,000 years (and 8 minutes) to reach you.