how does the sun burn

How Does the Sun Burn Without Oxygen?

Isn’t it a wonder that you need to blow oxygen into a bonfire to keep it going, but the sun can burn for billions of years without any oxygen at all?

How does the sun burn without oxygen to fuel it? We’re going to look through some of the science and help you understand how the sun burns the way it does. We’ll also go through some of the differences between the sun’s heat and the way things produce heat on earth.

We hope that the ideas below give you some useful insight into physics, chemistry, and the way our lovely sun shines down upon us. Let’s get started.

How Do Fires Work on Earth?

To get a full scope of the situation, let’s start by looking at how fires burn within our atmosphere.

In our earth’s atmosphere, fire requires oxygen, a fuel source, and heat. Without all of these things, the fire will never start. The fuel in this equation is anything that’s burning.

Most things on our planet could hypothetically burn when put in contact with enough heat. Heat can come as a result of friction, electricity, or something else. In the case of a match being struck, the friction between the surface and the match’s head creates enough heat to blend with oxygen and start the match on fire.

How Does Fire Catch?

When something gets warm, the atoms in that thing begin to move more rapidly. As it heats, the atoms jumble more and more, eventually moving so quickly that they break their own bonds. When those bonds are broken, the atoms are released and start to combine with the oxygen in the air.

The process of combining atoms with oxygen is called oxidation. That initial breakage of bonds and oxidation has to be enough to cause the same reaction in the fuel source.

When the fuel source catches on, the process of oxidation rumbles forward and keeps the fire going, using the fuel as a source of more energy and fire.

To conceptualize this, think about a lighter that doesn’t have much fuel. You spark it once or twice, and all you get is a little flicker. That flicker is an instance of brief oxidation without enough fuel to keep the chain of oxidation rolling.

No Oxygen, No Deal

The existence of fire is dependent upon the presence of oxygen. There’s lots of oxygen in the earth’s atmosphere, of course, so that’s never an issue here. We’ve got enough oxygen for trillions of organisms to breathe and millions of fires to start all of the time.

The further we move up into our atmosphere, though, the less oxygen there is to work with. That’s why we get lightheaded and sick when we reach extreme altitudes.

After about 620 miles, the atmosphere ends and we’re entirely out of any of the gasses (like oxygen) that compose our atmosphere. That means we don’t have the components needed for a fire.

So, how does the sun stay burning without oxygen if the whole process relies on oxidation?

How Does the Sun Burn Without Oxygen?

The sun rages on in space because it doesn’t “burn,” or combust. Instead, it releases energy through the process of nuclear fusion.

Fusion is a term that people use often, but it’s rare that we take the time to actually understand it. You might have had a good grasp of “fusion” in your middle school science class, but it’s a complicated process that we tend to forget.

Let’s look at what fusion is before we move on to thinking about the sun in space.

What Is Fusion?

Simply put, fusion occurs when two light atoms merge to become one. Sounds pretty easy to understand, right?

When we look closer, we see that fusion occurs only under extreme pressure and in extreme heat. The two atoms in question are typically of the same charge as well, so they repel each other.

Atoms that repel each other need to be brought together by gravity that overwhelms the repulsion of similar charges. The sun has an incredible density, accounting for more than 98 percent of all of the mass in our solar system.

In the case of our sun, the primary elements in question are hydrogen and helium. The sun’s core is made mostly of hydrogen atoms. When you take two hydrogen atoms and join them through the process of fusion, you create a helium atom.

How Do Stars Burn: Fusion

There are very few instances when fusion occurs. It’s generally only in the heart of stars that fusion takes place.

This is because stars are the largest, densest masses in particular solar systems. This is why they’re always the center of a solar system unless they’re rotating around one another. Stars are incredibly large, and when something reaches a critical mass, it has enough gravity to start ramming its similarly charged atoms into each other.

As you press and press those atoms together, their inherent movement gets restricted, heat is created, and you eventually see that the atoms will merge. In that process, atoms that get close to one another start to slam into each other an unimaginable number of times in only a few seconds.

Billions and billions and billions of collisions occur each second in the heart of the stars. Our sun is no different, which is why it’s the source of incredible amounts of light and energy created through the process of fusion.

Why Does Fusion Create Energy?

This is where Einstein’s famous “E=mc^2” equation comes in handy.

As hydrogen atoms smash into one another and join, they lose a little bit. In the process of joining, they must release a tiny amount of mass. The mass they lose comes from the energy that was previously used to hold each respective atom together.

That infinitesimal amount of mass gets released and turns into energy. Our famous equation tells us that energy equals mass times the speed of light squared. Just for reference, the speed of light is around 186,000 miles each second.

When you square something, you multiply it by itself. Further, the “mass” and “speed of light” in the equation need to be multiplied together before they’re squared. So, an easier way to look at the equation might be “energy=(mass times the speed of light) multiplied by (mass times the speed of light).”

The point is that even a small amount of mass becomes a monstrous amount of energy when it gets transferred.

How Much Mass Turns into Energy in the Sun?

Every day, more than 5,000,000 tons of mass get converted to energy within the sun. Multiply 5,000,000 tons by the speed of light, and then multiply that number by itself, and you get the amount of energy released from the sun every single day.

It’s an astounding amount of energy, but it’s what lights our world and provides us with life. You might be thinking, “how does the sun keep burning if it loses 5,000,000 tons each day?”

That’s a very good (and important) question. Let’s explore that.

How Does The Sun Keep Burning?

To start, let’s note that the sun could fit the earth inside of it more than 1 million times. Think about the massive, breathtaking size and beauty of the earth.

Imagine how many years it would take you to walk the circumference of the earth. Multiply this sphere by roughly 1.3 million times and you get the full vastness of the sun. In that vast orb, we get the photosphere, chromosphere, and corona.

These components make up the exterior of the sun much as our atmosphere and stratosphere do. The photosphere is where most of the heat is produced, and it’s the only part of the sun we can see with the naked eye. The corona is at the outer reaches, millions of miles from the photosphere.

This is a massive star with a lot of material to burn through. All of the hydrogen in the sun’s core is enough to sustain it for about another 3 billion years. So, we’ll have sunlight and energy for a very, very long time.

Over long periods of time, the sun might shrink slightly due to the loss of mass throughout the process of fusion. That’s not something that any one of us could ever notice, though, because it happens over the course of millions of years.

What happens when all of the hydrogen atoms dry up, though?

The Sun Will Die in 3 Billion Years

The sun will keep on fusing all of its hydrogen atoms into helium over the course of the next 3 billion years. At that point, it will run out of available hydrogen atoms and be left with a surplus of helium. The sun’s gravity isn’t powerful enough to merge helium atoms into one another to produce fusion.

Further, the outer core and atmosphere of the sun will still be there. The only difference will be that there’s not a significant mass of hydrogen there to provide fuel and mass for this star.

As the hydrogen leaves, the gravitational pull of the sun diminishes. When that happens, all the contents of the sun will expand and it will occupy much more space than it does now. The surface will cool slightly, and the star will become what’s known as a “red giant.”

Throughout that process, planets will be absorbed and disintegrated into the sun’s orbit and ever-expanding outer reaches. When all is said and done, the sun will shrink down to roughly the size of the earth as it cools down and becomes what is known as a “white dwarf star.”

You can see examples of white dwarfs and red giants elsewhere in the galaxy, sometimes even from your backyard.

How Hot Does the Sun Burn?

Don’t worry about that last section. We’ve got a lot of time before the sun starts changing its ways at all.

A more pertinent question is one about the heat of the sun and what that means for us on earth. So, how hot does the sun burn these days?

It turns out that the sun burns at around 5.78 Kelvin. That’s around 27 million degrees Fahrenheit or 15 million degrees Celsius, depending on the measurement you use. The temperature changes slightly in different areas of the sun as well.

Interestingly, the corona of the sun is actually the hottest outer layer, coming in at around 17 million degrees Fahrenheit. The chromosphere and photosphere both hold temperatures well under 1 million degrees Fahrenheit.

Fusion Versus Oxidation Fires

So, the sun burns without oxygen through the process of fusion. This doesn’t require oxygen because the energy released is contained within the hydrogen atoms before they’re fused.

When fusion occurs, the small amount of mass that binds the atom gets released in the form of energy. Energy is exponentially more powerful after it’s converted from mass.

On the other hand, a fire on earth requires oxygen. Fires require oxygen fuel, and heat. When enough heat is applied to the fuel source, the atoms in that fuel start to release in the form of energy.

When that happens, the newly released atoms start to combine with the oxygen in the air. This is a process called oxidation, and it keeps the fire burning so long as there is enough fuel and available oxygen.

So, these are two different types of fires that burn in different ways. The way the sun burns produces far more energy than the fires we might start in our backyards. Instead, fusion produces unimaginable amounts of energy that fuel our lives and provide the earth with the building blocks for life.

Want to Learn More About Astronomy?

The next time someone asks you “how does the sun burn without oxygen?”, we hope you have a good answer for them! There’s a lot more to learn about when it comes to astronomy, though.

We’re here to help you with all of the answers you’ll need. Explore our site for more insights into the wide world of astronomy and to answer any burning questions you might have about the stars.