How Hot Is The Sun?

The Sun is something most of us take for granted day in and day out as we go about our busy lives. But when you really get down to it, it is the basis for all life on Earth, including us humans. All of the animals on the land and in the oceans, the lush green plants, golden fields of wheat and other crops, and even the deep blue sky on a perfect summer day owe their existence to the Sun. Think about what would happen if the Sun would go completely out of existence – I know that this would be very unlikely to happen, but what would the Earth be like then? Temperatures would drop precipitously and very soon the Earth would start turning into a frozen wasteland gradually drifting toward Absolute Zero(-459.67 degrees Fahrenheit) over the eons of time. The oceans would freeze, and even the air would first turn to liquid(Nitrogen liquifies at -320 degrees Fahrenheit and Oxygen liquifies at -297 degrees Fahrenheit) and then freeze solid. There would be no more life on Earth of any kind – no humans, no animals, no plants, – not even insects or bacteria – NOTHING. And there would be no more deep blue skies to look at and enjoy on golden summer days.

This brings us to our question – how hot is the Sun – how hot does it really have to be to radiate its life-giving warmth over such a great distance of about 93 million miles? Well, the quick answer is that the Sun’s temperature varies from 10800 degrees Fahrenheit at the surface to about 27000000 degrees Fahrenheit at its inner core, or center. Now that’s really hot! Even the surface temperature of about 10800 degrees Fahrenheit is hot enough to turn every metal on Earth into a gas. And at the extreme temperature and pressure at the center of the Sun, matter its self exists only in a plasma state – the so-called fourth state of matter. In this super energetic state, even the electrons are stripped away from the nuclei of the atoms.

Why Is The Sun Hot?

Now, this really brings us to our next question – why is the sun hot? Well, the process ocurring in the Sun is very similar in some respects to a hydrogen bomb explosion, although it does differ in some other ways. The hydrogen bomb explosion creates an incredibly hot plasma in the millions of degrees Centigrade which fuses hydrogen atoms into helium atoms thus releasing a tremendous amount of energy in the form of heat and radiation. And all of this occurs in only a brief fraction of a second – at least that’s for the actual plasma state itself. So you could almost think of this as a very unstable ‘mini’ sun lasting for only an incredibly brief amount of time. Why is it so unstable compared with our Sun? Basically, it is because the amount of hydrogen fuel is ‘jillions’ of times smaller than that of the Sun as well as the fact that gravity doesn’t come into play to have a stabilizing role. So the reaction occurs very, very quickly.

In the Sun hydrogen nuclei are also fused into helium nuclei in a plasma state which is roughly 27000000 degrees Fahrenheit in the core. This process is known as proton-proton fusion in the Sun since the electrons are stripped away in this highly energized plasma state with only the hydrogen nuclei, a single proton, remaining. Taking place in the core of the Sun, this is the reaction primarily responsible for the Sun’s release of energy, effectively making the Sun ‘hot’. Please be aware that this reaction in the inner core of the Sun is responsible for about 99 percent of the heat produced by the Sun, which then radiates outward through the whole Solar System. Naturally, since this is a three-dimensional process, the amount of heat received at a given distance from the Sun should be inversely proportional to the cube of the distance from the Sun. This result is simply obtained by taking the area of a given radius, pi r squared and giving it one complete rotation through the third dimension, then integrating the various ‘slices’ to give the formula for the volume of a sphere – 4 thirds pi r cubed. Note that the surface area of a sphere is not used since the distance from the Sun would be variable and not fixed, therefore showing this nonlinear dropoff rate in energy(and heat) received. So there is a rather rapid dropoff at the aforementioned nonlinear rate. Just think of any given distance from the Sun that is the radius of an imaginary sphere. Now this sphere would receive 100 percent of the Sun’s radiated energy, but for a celestial body of a fixed and definite size, the larger the sphere the more dilated the energy received – this relates to the body’s distance from the sun in the way previously described.

Certainly, it is easy to see why Mercury with it’s close proximity to the Sun(35 million miles – less than 40 percent of Earth’s) is so much hotter. Please note that our imaginary sphere thought experiment above does not take into account the varying degrees of eccentricity of the various planets in the Solar System nor does it account for the tilting of the planets axis. For example, Mercury has an eccentricity of .2056 in its orbit compared to .0167 for the Earths orbit which is fairly close to circular. There may also be varying amounts of cosmic dust and debris in the Solar System which could possibly vary the results somewhat as well.

Is The Sun A Controlled Thermonuclear Explosion?

Although perhaps not technically correct in a strict sense, I like to think of the Sun as a controlled thermonuclear explosion that literally takes billions of years to happen. The gigantic mass of the Sun creates an incredibly intense gravitational field that balances the huge release of kinetic energy from its core in the form of heat and radiation which prevents the Sun from collapsing in on itself. The gravity of the Sun is about 27.94g compared to .99732g for the Earth, which is about 28 times as much! This, of course, is the result of the Sun’s mass which is roughly 4,000,000,000,000,000,000,000,000,000,000 pounds – or put another way 4 million trillion trillion pounds! The Sun actually has 99.8 percent of the mass of the entire Solar System and 333000 times the mass of the Earth! So the result is this giant shining ball that is relatively stable and should remain so for billions of years into the future until the Sun has used up enough of its fuel and eventually goes through various changes, the form and extent of which are dependent upon the mass and temperature of the Sun and some other factors as well. In this proton-proton fusion reaction, the Sun burns up about 800 billion pounds of hydrogen per second and will gradually use up its fuel over the course of billions of years because of its gigantic mass, converting hydrogen to helium and then to progressively heavier elements until the element iron is reached, where the reaction stops since to fuse heavier elements the energy input would be greater than the resulting output.

But eventually, in a far distant future that we can hardly imagine, even the Sun will die. In about 1.2 billion years the Sun will begin to change as the hydrogen fuel in its core is used up. At first, it will grow brighter and the radiation(including heat) it emits will greatly increase – this will cause the mean surface temperature of the Earth to go from a little less than 70 degrees Fahrenheit where it is now to almost 170 degrees Fahrenheit. These are mean temperatures, including the poles – highs would be much greater than 170 degrees Fahrenheit. So much so in fact that even the oceans would boil and evaporate away turning the Earth into a stark, lifeless desert. Then when it reaches an age of 5 to 8 billion years old, the Sun will run out of hydrogen fuel completely. The resulting leftover helium in its core will cause it to become unstable and swell to a significantly greater size. For about 700 million years, the Sun will grow brighter until it is twice as bright as it is now. After this time the Sun will start cooling off and swell even larger, becoming what is known in Astronomy as a Red Giant, a huge luminous star approaching its final stages of evolution. It would appear as a giant red glowing ball hanging in the sky, but there would be no one around to see it. And then in a far, far distant future, the Sun would dim out completely and would be no more – the Sun is not massive enough to become a Black Hole. But enough of this gloomy talk – this is many billions of years in the future and humans will not exist in their present form, if they exist at all. The hope would be that the human race will have evolved to a much higher form and be somewhere else in a much more pleasant situation.

The Sun – Earths Best Friend

We’ve learned that the surface temperature of the Sun is about 10800 degrees Fahrenheit and the inner core is an incredible 27000000 degrees Fahrenheit. This heat radiates outward from the Sun and goes throughout the Solar System, giving Earth its life-giving warmth. We also know that without the Sun there would be NO life of any kind on Earth – nothing at all. No animals, no plant life, no people, not even insects. But because the Sun does exist the Earth is abundant with an incredible diversity of life, all the way from the very smallest imaginable to huge, even giant, animals like elephants and whales. There was a time in Earths history when these incredibly huge creatures called dinosaurs were roaming around, that is before they went extinct millions of years ago. The Sun is in a very true sense the Earths best friend. Just try to remember that the next time you are enjoying a warm, lazy summer day with puffy white clouds floating in a deep blue sky.