How Hot Is the Sun? Sun Temperature


How Hot Is the Sun
The temperature of the Sun varies, from 5500 C (10,000 F) on its surface up to 15 million C (27 million F) at its core.

Have you ever wondered just how hot the Sun is? It’s not a single temperature because the Sun consists of layers where different processes occur. From the fiery depths of its core to the outermost reaches of its corona, here are the temperatures, from millions of degrees in Kelvin to the more comprehensible Celsius and Fahrenheit scales.

  • The hottest part of the Sun is the core: 15 million K; ~15 million °C; 27 million °F.
  • The coolest part of the Sun is the visible surface or photosphere: 4,000 – 6,500 K; ~5,500 °C; ~10,000 °F.
  • Surprisingly, the solar atmosphere or corona is hotter than the Sun’s surface. Also, the temperature is quite variable: 500,000 – 2,000,000 K; ~2 million °C; ~ 3.5 million °F.

Core

The core, where nuclear fusion occurs, is the hottest part of the Sun. Here, hydrogen atoms fuse to form helium, releasing immense energy.

  • Temperature: Approximately 15 million Kelvin (K)
  • In Celsius: Around 15 million °C
  • In Fahrenheit: About 27 million °F

This intense heat overcomes the strong nuclear force between protons, allowing fusion to occur.

Radiative Zone

Surrounding the core, the radiative zone is where energy moves outward via radiation. The temperature gradually decreases in this zone.

  • Temperature: Roughly 7 million K
  • In Celsius: Approximately 7 million °C
  • In Fahrenheit: Around 12.6 million °F

In this zone, photons bounce around, taking a long time to travel through due to the high density of solar material.

Convective Zone

In the convective zone, energy is transported by convection currents, similar to boiling water.

  • Temperature: About 2 million K
  • In Celsius: Near 2 million °C
  • In Fahrenheit: Close to 3.6 million °F

Hot plasma rises, cools as it nears the surface, then sinks back down to be reheated, creating convection cells.

Photosphere

The photosphere is the visible surface of the Sun.

  • Temperature: Roughly 5,500 K
  • In Celsius: About 5,300 °C (usually rounded up to 5.500 °C)
  • In Fahrenheit: Approximately 9,500 °F (usually rounded up to 10,000 °F)

This layer emits the light we see, appearing bright due to the contrast with cooler outer layers.

Chromosphere

Above the photosphere is the chromosphere, a layer visible during solar eclipses as a reddish glow.

  • Temperature: Around 4,000 to 20,000 K
  • In Celsius: Between 3,500 and 20,000 °C
  • In Fahrenheit: Approximately 6,700 to 35,500 °F

This layer shows an interesting temperature rise, thought to be influenced by magnetic fields.

Corona

The corona, the Sun’s outermost layer, is surprisingly hotter than the layers beneath it.

  • Temperature: Ranges from 1 to 3 million K
  • In Celsius: About 1 million to 3 million °C
  • In Fahrenheit: Around 1.8 million to 5.4 million °F

The corona’s higher temperature than the photosphere is a subject of scientific study. One theory is that magnetic waves carry energy from the Sun’s surface to its outer layers, heating the corona.

How Do We Know How Hot the Sun Is? Measuring the Sun’s Temperature

Scientists apply several methods for measuring or calculating the Sun’s temperature:

  • Spectroscopy: Spectroscopy analyzes the spectrum of light from the Sun to determine temperature based on emission and absorption lines.
  • Solar Probes: Instruments on spacecraft measure various properties of the Sun, providing direct temperature data.
  • Radio Telescopes: Telescopes measure the intensity of the Sun’s radio waves to infer temperature.
  • Stellar Models: The primary method for estimating the core temperature of the Sun involves theoretical models of stellar structure and evolution. These models take into account various physical principles, including nuclear physics, thermodynamics, and fluid dynamics.
  • Nuclear Fusion Rates: By understanding the physics of nuclear reactions (specifically the proton-proton chain dominant in stars like the Sun) and the rate at which energy is produced, scientists estimate the necessary core temperature for these reactions to occur at the observed rate.
  • Helioseismology: This is the study of oscillations and waves in the Sun. By observing sound waves that travel through the Sun and emerge at its surface, scientists infer a lot about the internal structure of the Sun, including temperature gradients.
  • Solar Neutrinos: Neutrinos are elementary particles produced by the nuclear reactions in the Sun’s core. They interact very weakly with matter, meaning they escape the Sun’s core and reach Earth almost unimpeded. By detecting and studying these solar neutrinos, scientists gain insights into the nuclear reactions occurring in the core.
  • Comparative Analysis with Other Stars: Astronomers also compare the Sun with similar stars (main-sequence stars of similar mass and composition). Observations of these stars, alongside theoretical models, provide additional context for understanding the Sun’s internal processes.

How Hot Is the Sun Compared With Other Stars?

The Sun is a G-type main-sequence star, and there are both hotter and cooler stars in the universe.

  • Hotter Stars: Blue giants like Rigel are much hotter, with surface temperatures exceeding 10,000 K.
  • Cooler Stars: Red dwarfs like Proxima Centauri have surface temperatures as low as 3,000 K.

Each star’s temperature depends on its size, age, and composition, influencing the nuclear fusion processes within.

Temperatures on Earth That Are Hotter Than the Sun

On Earth, the hottest temperatures are in particle accelerators and fusion reactors:

  • Particle Accelerators: In experiments with particle accelerators like the Large Hadron Collider (LHC), temperatures have momentarily exceeded the core temperature of the Sun. For instance, collisions of heavy ions create a state of matter known as quark-gluon plasma, with temperatures estimated to be over 5 trillion Kelvin (5,000,000,000,000 K). These temperatures are brief and occur in an incredibly small space.
  • Fusion Experiments: In fusion research, experiments aim to replicate the conditions inside the Sun to achieve nuclear fusion. The ITER (International Thermonuclear Experimental Reactor) project, for instance, aims to reach temperatures of around 150 million Celsius (150,000,000°C), which is about 10 times hotter than the core of the Sun. However, these temperatures haven’t been fully achieved yet.

References

  • Goupil, M.J.; Lebreton, Y.; Marques, J.P.; Samadi, R.; Baudin, F. (2011). “Open issues in probing interiors of solar-like oscillating main sequence stars 1. From the Sun to nearly suns”. Journal of Physics: Conference Series. 271 (1): 012031. doi:10.1088/1742-6596/271/1/012031
  • Marshall Space Flight Center “The Solar Interior.” Solar Physics.
  • Mullan, D.J (2000). “Solar Physics: From the Deep Interior to the Hot Corona”. In Page, D.; Hirsch, J.G. (eds.). From the Sun to the Great Attractor. Springer. ISBN 978-3-540-41064-5.
  • Phillips, K.J.H. (1995). Guide to the Sun. Cambridge University Press. ISBN 978-0-521-39788-9.
  • Shu, F.H. (1982). The Physical Universe: An Introduction to Astronomy. University Science Books. ISBN 978-0-935702-05-7.