How hot is the Sun? | Surface Temperature & Variance

The Sun is nearly a perfect sphere of hot plasma. The average surface temperatures are at around 5.778 K, but they vary since it is composed out of three layers.

Our Sun is an enormous energy and light-producing sphere of glowing gases. Though it is the hottest object in the solar system, other stars are far hotter, even tens of times so.

But how hot is the Sun? This question is a bit tricky to answer since this celestial object varies tremendously in temperatures, but here are some things to consider.

Nuclear Fusion

In the Sun’s core, gravitational attraction produces immense pressure and temperature. Some estimates put the temperatures at 27 million degrees Fahrenheit / 15 million degrees Celsius. The process of nuclear fusion occurs when hydrogen atoms are compressed and fused together, creating helium.

This process creates vast amounts of energy, and it radiates outward to the Sun’s surface, atmosphere, and beyond. From the core, energy moves to the radiative zone, where it bounces around for up to 1 million years before moving up to the convective zone, the upper layer of the Sun’s interior.

Temperatures here drop below 3.5 million degrees F / 2 million degrees C. Large bubbles of hot plasma form a soup of ionized atoms and move upward to the photosphere.

Photosphere

The Sun’s photosphere has been estimated to have temperatures at about 10.000 degrees F / 5.500 degrees C. In this region, the Sun’s radiation is detected as visible light.

Sunspots on the photosphere are colder and darker than the surrounding area. In the center of the big sunspots, temperatures can be as low as 7.300 degrees F / 4.000 degrees C.

Chromosphere

When it comes to the chromosphere, the next layer of the Sun’s atmosphere, it is far cooler. Estimated temperatures are at about 7.800 degrees F / 4.320 degrees C.

The visible light from the chromosphere is often too weak to be seen against the brighter photosphere.

However, during total solar eclipses, when the Moon blocks the photosphere, the chromosphere can be seen as a red ring around the Sun. Viewing it without protection can lead to permanent eye damage.

But why does it appear red? Scientists believe that it is because of the presence of large amounts of hydrogen.

Corona

Here is where everything changes drastically. In the corona, temperatures rise though the light can only be seen during an eclipse as plasma streams like the points on a crown.

In comparison to the rest of the Sun’s body, temperatures rise drastically, ranging from 1.7 million degrees F / 1 million degrees C, up to more than 17 million degrees F / 10 million degrees C.

Thus, the Sun’s corona is hundreds of times hotter than its layers below. What is interesting is that we assumed the temperatures to be the coolest in the outermost layer when, in fact, this isn’t the case. The corona cools in time, and as its losing heat and radiation, matter is blown off as the solar wind, which occasionally crosses the Earth’s path.

In our solar system, the Sun is the largest and most massive object at a distance of roughly 93 million mi / 149.5 million km from Earth or 1 AU. Because of this distance, the Sun’s light and heat actually reach the Earth in about eight minutes or light-minutes.

Comparison with other stars

Our Sun is quite a typical star in the Universe, and when we compare some of its features, especially its temperatures, we once again realize how vast is the world we live in.

Some of the hottest stars in the Universe may reach up to 100.000 degrees Fahrenheit; as such, they are at least ten times hotter than our Sun.

But these are the estimatives of just the surface temperatures. Inside the core, temperatures are genuinely astonishing. Some stars reach about 200 million degrees inside their cores or more than eight times the Sun’s core temperatures.

There is another thing to consider when certain stars end their lives in massive explosions; the inside temperatures could reach as high as 10 billion degrees.

Though these estimates are hard to fathom, we can be thankful that our Sun is among the most common types of stars in the Universe, which generally have, at least as we currently understand, the right temperatures for life to develop.

Coming back at our solar system, distance from the Sun or a star in general, doesn’t necessarily mean cooler temperatures. Take Mercury, for example.

Even though it is the closest planet to the Sun, it isn’t the hottest. Venus instead takes the first place as the hottest planet of our solar system. But this is only because Venus has an awkward atmosphere that traps heat inside.

The Future

Every star reaches the end of its life at a given point in time. Our Sun will also come to this, but it is unlikely that anyone will be alive at the time to witness it.

Scientists have studied the Sun and reached the conclusion that it will live for another 5 billion years based on its fuels. When it depletes its hydrogen supplies, our Sun will begin to expand and envelope the inner planets, including Earth.

At this stage, our Sun will inevitably become a red giant. It will continue to burn as a red giant for about a billion years. When the last fuels are depleted, it will become a white dwarf.

Did you know?

You would need more than one million Earth’s to fill the Sun.
Though there are so many planets and other celestial objects in the solar system, the Sun actually comprises about 99.86% of the mass in the solar system.
The Sun rotates more quickly at its equator than at its poles while it also rotates in the opposite direction to Earth.
The Sun has the most powerful magnetic field in the solar system, and it is also self-regenerating though the process is still not understood.