How Old Is The Sun? When & How Will It Die?

How Old Is The Sun? When & How Will It Die?

Remember in the movie Interstellar when Michael Caine’s Professor Brand gives Matthew McConaughey’s Cooper a tour of the facility?

Cooper says, “now you need to tell me what your plan is to save the world”. And Professor Brand replies, “We’re not meant to save the world, we’re meant to leave it”?

Some people called it escapist, but there here’s one reason why they think the way they do.

Ready? Let’s get started.

How Old Is The Sun? When & How Will It Die: Short Summary

Astronomers have predicted that the sun has a lifespan of roughly 9 or 10 billion years. At the moment, we know that the sun is 4.6 billion years old.

So, in the next five billion years or so, its core will shrink and the sun will turn into a red giant ball of energy. During this time, the outer layers of the sun will expand and engulf everything in its path.

Watch: How Old Is the Sun

How Do We Know How Old the Sun Is?


The sun is a big and bright star in space. It is the main source of light and heat for all the planets we have discovered so far. So, it is natural for us to wonder if this is going to last forever. As always, the answer is no.

How do we know when the end is near? To ascertain that we need to answer the following questions:

  • How old is the sun?
  • How does it age?
  • Is there an expiry date to all its wonderful gifts?

There are several scientific methods based on which the age of the sun can be calculated. One of the techniques that has proven to be efficient is to gauge the age of all the other objects that were formed around the same time as the sun.

These are objects that exist in our solar system, which is why we can reasonably presume that the process of life and death will be similar, if not the same. Some of these objects are also stars like the sun itself. Hence the presumption.

The technique used to determine the sun’s age is radioactive dating. This was used to determine the age of some of the oldest meteorites in our solar system which are also 4.5 billion years old.

The sun belongs to the G-type main sequence stars. They are also called yellow dwarfs and live for about 9 or 10 billion years. So, if the sun is about 4.6 billion years old, we know that it has about 5 billion more years before it starts dying.

Now, we also know that the energy in the sun comes from nuclear fission reactions that take place at its core. But those reactions will come to a standstill at some point and that’s when the star will die.

In the 5 billion years that it will take the sun to die, it will grow in size and become cooler. It will all happen at the same time and when it comes to an end, the sun will become a red giant, which is why we call it that.

But since it grows in size, the sun is estimated to also become roughly 2,000 times brighter compared to what it is today. If it is cooler than today but bigger and brighter, what happens to us humans?

Turns out that is not our problem at all and we’ll tell you all about that in just a moment.

Why Will the Sun Die?


As you know, the sun is a gas cloud made mostly of hydrogen and helium. At any given point in time, many fission reactions are taking place inside the sun that involves using hydrogen atoms. Eventually, the pressure becomes so high that the gases cannot handle it.

At these enormous temperatures and pressure, hydrogen atoms will lose their electrons in them and fuse with the helium atoms.

This phenomenon will release so much energy that the sun’s gravity will no longer be powerful enough to hold the cloud of gas and the star will collapse. At the moment, though, the sun is as stable as it has even been since this solar system was formed.

What Will Happen after the Sun Dies?


We know that after these remaining 5 billion years left on its contract, the sun will turn into a red giant. And it will stay that way for about a billion years. Now, if you’re wondering what comes next, the experts are a bit fuzzy on the details.

Many studies have found that we need a star that has about two times the mass of the sun for the formation of a bright planetary nebula. But through computer modeling, we learned in 2018 that the sun would eventually shrink from its red giant state and become a white dwarf and then become a regular planetary nebula.

That’s what happens to the sun. Scary or beautiful as this all sounds, why is the death of the sun not our problem? It is, after all, our main source of light and heat. That’s next.

What Happens to the Earth Then?


The answer to this question could be looked at as good news or bad news, depending on your philosophical bend. The death of the sun is not our problem because the Earth will be dead long before all this starts to unfold.

The process of the sun’s death takes a long time to play out as you might have already figured. This process starts off with the hydrogen atoms in the sun getting used for nuclear fissions which keep the bright star burning bright.

But as the hydrogen atoms get used, the core of the sun becomes smaller and smaller. And as that happens, the temperature rises which causes the hydrogen atoms to lose their electrons and become what are called naked hydrogen atoms.

These naked hydrogen atoms are then ready to fuse with the helium atoms. As more hydrogen atoms get used, more of them are available to fuse with helium atoms. This fusion reaction upsets the sun’s gravitational force.

The fusion reaction makes the sun brighter by increasing its luminosity by 1 percent every 100 million years. As a result, the sun will be 10 percent brighter in just over a billion years, 1.1 billion to be precise, than it is today.

As the sun becomes brighter, the Earth will get more energy to absorb.

Sounds like a good thing? It’s not.

Because the Earth will become a little too hot and most living species won’t be able to survive that. By the time this happens, the polar ice caps would have vanished entirely, the oceans would be at boiling temperatures and the water vapor that comes from everything that’s evaporating will escape the Earth’s atmosphere.

So, there will be no rains and the Earth will turn into a dry and hot planet like Venus.

In fact, while the sun is undergoing these changes, so will planet Earth’s orbit. Now, you may be thinking that maybe the orbit changes such that we don’t get engulfed by the red giant. But by then, the Earth would’ve already become uninhabitable.

So, by current calculations, the Earth is expected to welcome life as we know it only for about a billion years.

Frequently Asked Questions


Q: Theoretically, How Will Humans Survive without the Sun?

A: We will never have to find out but, for starters, without sunlight, there won’t be any photosynthesis which will kill most plants. The life that survives that phenomenon will still fall victim to the lack of heat. And without that, life on this planet, if there’s any, will cease to exist.

Q: What Would Happen If the Sun Went Out for a Second?

A: The gravitational force which determines the Earth’s orbit depends on factors like its interaction with the sun. So, if there is no sun, the planets wouldn’t even be orbiting in the elliptical path as they do now. Instead, they will travel in a straight line and there would be unnecessary interactions with other objects in their path.

Q: Can the Earth Survive without the Moon?

A: Planet Earth can survive for about 6 to 12 hours without the moon. The moon’s pull has a strong influence on the Earth’s rotation which makes sure that our days are no more or less than 24 hours long. Without the moon, that count gets upset and there’s no telling how many days would be in a year.

Conclusion & Summary

The sun is of the category of stars that are expected to live for 9 to 10 billion years. At the moment, we know that the sun is about 4.6 billion years old, which means it is quickly reaching its halfway mark.

But in the second act, the hydrogen atoms in the sun will fuse with helium atoms. As a result, the sun will become bigger, brighter and cooler. Eventually, it will become a red giant swallowing every object in its path. But we don’t have to worry about it because the Earth will potentially last for only a billion years from now.

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