The Sun is the largest object in our Solar System and accounts for approximately 98% of its total mass. 1.3 million Earths could fit inside the Sun.
The Sun is located at the center of the system, in such a way that all other objects, such as planets, asteroids and comets, and all the satellites associated with these objects, revolve around it.
The energy we receive from the Sun is generated at its core, where nuclear fusion takes place. There, pressure and temperature are so high that hydrogen atoms are fused into helium atoms, releasing huge amounts of energy.
Our star is incredibly hot. But what is the temperature of the Sun?
The temperature is not the same throughout the Sun
The Sun is divided into layers, and each layer has a different temperature. The Sun is hotter at its core and colder at its outer layers.
The Sun’s Core
With about 139,000 kilometers (86,370 miles) of the Sun’s radius, this is the central region of the star and, therefore, the most massive and hottest area. The conditions are so extreme that nuclear reactions take place.
These reactions transform hydrogen atoms into helium, and the difference in mass is expelled as energy and carried to the surface of the Sun, through a process known as convection, and is released in the form of light and heat.
The energy generated inside the Sun takes a million years to reach the surface. Every second, 700 million tons of hydrogen are converted into helium ash.
During this process, 5 million tons of pure energy are released; therefore, as time goes by, the Sun is becoming lighter.
What is the temperature of the Sun’s core?
The temperature of the Sun’s core is 15,000,000 °C, and the pressure is 340 billion times Earth’s atmospheric pressure at sea level.
The radiation zone, or radiative zone, is the layer that comes after the core. The energy produced in the core is transported here slowly through the absorption and emission of photons.
The transport of energy in the radiation zone is a very slow process. The energy produced in the core takes around a million years to leave the radiation zone.
The temperature at the radiation zone ranges from 2,000,000 ºC to 7,000,000 ºC
The convective zone is the layer above the radioactive zone. It is responsible for transporting energy generated at the core to the Sun’s surface.
In this region, which has about 15% of the Sun’s radius, energy is transported by convection currents through the movement of large blocks of very hot matter.
The temperature at the convection zone is about 2,000,000 °C.
The photosphere is the Sun’s outer shell. This layer is made up of several very small hexagonal structures called granules.
These structures resemble a boiling liquid. Its turbulent appearance is due to the energy eruptions that occur there.
What is the temperature of the Sun’s photosphere?
The temperature of the Sun’s photosphere ranges from 4,125 ºC to 6,125 ºC.
Although the chromosphere is just above the photosphere, this layer is not visible, because the radiation emitted by it is weaker than the radiation from the photosphere.
But it is possible to observe the chromosphere during eclipses, when the Moon hides the disk of the photosphere. The chromosphere is 3,000 to 5,000 kilometers (1,864 to 3,106 miles) deep.
Solar energy passes through this region on its way from the center of the Sun. Solar spots (faculae) and explosions (flares) form in the chromosphere.
Faculae are bright clouds of hydrogen that appear in regions where sunspots will soon form. Flares are shiny filaments of hot gas emerging from the sunspots.
What is the temperature of the Sun’s chromosphere?
The temperature of the Sun’s chromosphere is 19,725 ºC.
This is the outermost layer of the Sun, where huge clouds of gas coming out of the chromosphere, called prominences, are visible.
The corona is formed by particles that slowly move away from the Sun, which can be seen during a total solar eclipse.
Currently, the corona can be studied with the aid of a device called a coronagraph.
The brightness of the corona is comparable to that of the full moon, being overshadowed by the brightness of the photosphere.
What is the temperature of the Sun’s corona?
The temperature of the Sun’s corona ranges from 500,000 ºC to 6,000,000 ºC.
The high temperature of the corona must be maintained by a constant energy supply. Due to this high temperature, the gases in the corona region become diffuse, so the total energy stored is low.
Gradually these gases turn into solar winds, which is a flow of particles from the Sun that reaches the entire Solar System.
The gas lost in this process is replaced with new material from the chromosphere.
What is the hottest layer of the Sun?
The core is the Sun’s hottest layer.
Inside the core, temperatures are always above 15 million degrees Celsius. As you approach the surface of the Sun, temperatures drop.
In the photosphere, temperatures drop to around 5,900 degrees Celsius.
In some darker areas, called sunspots, temperatures are even lower, at around 3,500 degrees Celsius.
However, in the corona, temperatures can reach an astonishing 6,000,000 degrees Celsius, still lower than the core’s temperature.
How do we measure the temperature of the Sun?
One thing is for sure: there is no way to use a thermometer on the Sun. Fortunately, there are many ways to calculate the temperature of the Sun.
One of them is by using a spectrometer. This scientific instrument separates the light emitted by the star in several lines.
Each line corresponds to a chemical element found in the Sun. Since each chemical element absorbs heat differently, it is possible to calculate how hot the star is.
Another way to measure the temperature of the Sun is through the radiation emitted by it.
The method consists of placing a metal plate to receive light directly from the Sun and checking how much heat it absorbs.
Then, scientists use that information in a formula, taking into account the distance between the Earth and the Sun.
The future of the Sun
The Sun has been active for 4.6 billion years and has enough fuel to continue for approximately another five billion years.
At the end of its life, the Sun will begin to fuse helium into heavier elements and expand, eventually growing so large that it will swallow the Earth.
After a billion years as a red giant, it will quickly collapse into a white dwarf – the end product of a star like ours. It can take a trillion years for it to cool down completely.
Amazing images of the Sun produced by NASA: