Why Does the Sun Shine?

Ethan vanderWilden, AS151, Professor McGrath, 11/3/16

A Shining Star:

Why Does the Sun Shine?

Why does the Sun shine? Well, that seems like a pretty important question. Let’s think; if the Sun didn’t shine, it would be very very cold. Also, it probably wouldn’t “be” anything because we certainly would not even be alive. The Sun’s shining gives us light and heat, two things that humans have been depending on for their entire existence.

Look at all the light and heat!!!

http://www.nasa.gov/sites/default/files/images/480273main_20100904-limb.jpg

There have been multiple explanations for why the Sun shines, all having to do with some form of potential energy being converted into a type of kinetic energy called radiative energy. Have you ever heard of sunlight? Well that is basically radiation from the Sun, which is radiative energy being given off by the Sun.

One explanation for why the Sun shines is that chemical potential energy is being converted into radiative energy. This means that the Sun is essentially burning some fuel source, similar to a car converting gas into kinetic energy to get the vehicle moving. However, this explanation has been exemplified as false. If we look at the mass of the Sun, and convert that mass into all of the energy that it could yield from being burned as fuel, the Sun could only shine (aka give off radiative energy) for about 9000 years. However, our solar system has existed for close to 4.5 billion years, so this cannot be the answer.

            

The ideas of converting either chemical or potential energy into radiative energy for the reason that the Sun shines are incorrect

(In order left to right, link sends you to page) 1 2 3 4

Another explanation is that gravitational potential energy is being converted into radiative energy. This means that the Sun is collapsing in on itself, and just as when someone jumps off of a diving board, they gain speed, the Sun would produce more kinetic energy. Similar to the chemical energy theory, if we look at the mass and radius of the Sun, and look at the amount of gravitational potential energy that could be converted into radiative energy, the Sun could only shine for around 30 million years. While this is certainly an improvement, it still struggles to account for the 4.5 billion year existence of our solar system. However, while gravitational contraction does not account for the Sun shining now, in the early stages of our Sun's history, gravitational contraction led to enough energy produced to heat the Sun's core to a temperature where nuclear fusion can occur.

The explanation of mass-energy conversion into radiative energy seems popular and accepted. Here, using Einstein’s E=mc^2, mass is converted into energy. The Sun has enough mass so that its nuclear potential energy could support the Sun shining for 10 billion years. This is well within our range of the solar system existing for the past 4.5 billion years. Now that this method is accepted, the question is: how does the process work (aka HOW does the Sun shine)?

Here, four Hydrogen atoms become one Helium atom, with gamma rays as a byproduct
https://en.wikipedia.org/wiki/Nuclear_fusion

Within the 10-15 million degree (Kelvin) core of the Sun, a process known as fusion occurs. Fusion can only happen under circumstances of high temperatures (greater than 10 million kelvin) and high densities, both of which exist in the core of the sun. At high speeds, the nuclei from Hydrogen atoms come close enough together for a force known as the “Strong Force” to bind the two atoms together. Through this binding of Hydrogen, fusion leads to the formation of Helium atoms. During this process of four Hydrogen atoms becoming one Helium atom, a total of 0.7% of the initial mass of the four atoms is “lost” due to two energy carrying gamma rays being given off. This 0.7% of the mass Hydrogen atoms is the radiative energy that we’ve been talking about! Without gamma rays, the Earth would be a cold, dark place...if it even were a place. These fusion reactions are also responsible for some of the generation of heavier elements present in our Universe, which are essential for future planets to live as these elements are eventually recycled back into the Universe. Inside of the Sun's core, fusion is the essential function that keeps our solar system functioning and alive.