Sun

Sunspots and dark lines in the rainbow

People have long worshipped the Sun, and East Asian astronomers recorded naked-eye sunspots from before the Common Era. In the 1610s Galileo Galilei observed sunspots by telescope, publishing in 1613 and arguing from their motion that the Sun rotates. Around 1814 Joseph von Fraunhofer found hundreds of dark lines in sunlight's spectrum, and in 1859–60 Gustav Kirchhoff and Robert Bunsen showed that they are fingerprints of elements absorbing light in the solar atmosphere, founding spectroscopy. Helium was found in the solar spectrum in 1868, before it was found on Earth. In 1843 Heinrich Schwabe discovered that sunspot numbers rise and fall in a roughly 11-year cycle.

What makes the Sun shine?

In the 19th century the Sun was thought to burn like coal or shine by contracting, but that would last only tens of millions of years — too short for geology and evolution. In her 1925 thesis Cecilia Payne showed that stars, including the Sun, are mostly hydrogen and helium. In 1939 Hans Bethe calculated that energy comes from nuclear fusion of hydrogen nuclei into helium in stellar cores. The Sun's core is about 15 million °C, and about four million tonnes of mass are turned into energy every second. Energy from the core is estimated to take tens of thousands of years or more to cross the radiative and convective zones, while light — photons — leaving the surface reaches Earth in about 8 minutes 20 seconds. In 1968 Raymond Davis first detected solar neutrinos but found only about a third of the expected number — the solar neutrino problem — which Canada's SNO experiment resolved in 2002 by showing neutrinos change type in flight.

Solar activity, Earth and the future

The Sun is a ball of hot plasma whose tangled magnetic fields drive sunspots, flares and coronal mass ejections. In 1859 Richard Carrington saw the first recorded white-light flare; the geomagnetic storm that followed sparked telegraph lines and brought aurorae to low latitudes. In 1958 Eugene Parker predicted the solar wind, a continuous outflow of plasma, soon confirmed by spacecraft; NASA's Parker Solar Probe, launched in 2018, became the closest human-made object to the Sun. Strong solar storms can damage satellites, GPS and power grids, making space-weather forecasting important. In about five billion years the Sun is expected to exhaust core hydrogen, swell into a red giant and cool as a white dwarf — it is too small to become a black hole or neutron star. Never look at the Sun directly, through ordinary sunglasses or a telescope without a certified solar filter, as this can cause serious eye damage.

FAQ

What colour is the Sun?

Sunlight is a mix of nearly all colours and is close to white. It looks yellow by day and red at sunset because the atmosphere scatters blue light.

If the Sun vanished, when would we know?

Light takes about 8 minutes 20 seconds to reach Earth, so not until then. Changes in gravity also travel at light speed, so Earth's orbit would be affected only after about 8 minutes too.

Sources reviewed: 2026-10-26

References

1. Galilei, G. (1613). Istoria e dimostrazioni intorno alle macchie solari e loro accidenti. Roma: Giacomo Mascardi.
2. Fraunhofer, J. (1817). Bestimmung des Brechungs- und Farbenzerstreuungs-Vermögens verschiedener Glasarten. Denkschriften der Königlichen Akademie der Wissenschaften zu München, 5, 193–226.
3. Schwabe, H. (1844). Sonnen-Beobachtungen im Jahre 1843. Astronomische Nachrichten, 21, 233–236.
4. Carrington, R. C. (1859). Description of a singular appearance seen in the Sun on September 1, 1859. Monthly Notices of the Royal Astronomical Society, 20, 13–15.
5. Kirchhoff, G. (1860). Ueber das Verhältniss zwischen dem Emissionsvermögen und dem Absorptionsvermögen der Körper für Wärme und Licht. Annalen der Physik, 185(2), 275–301.
6. Payne, C. H. (1925). Stellar Atmospheres. Harvard Observatory Monographs No. 1. Cambridge, MA: Harvard Observatory.
7. Bethe, H. A. (1939). Energy production in stars. Physical Review, 55(5), 434–456.
8. Parker, E. N. (1958). Dynamics of the interplanetary gas and magnetic fields. Astrophysical Journal, 128, 664–676.
9. Davis, R., Harmer, D. S., & Hoffman, K. C. (1968). Search for neutrinos from the Sun. Physical Review Letters, 20(21), 1205–1209.
10. Ahmad, Q. R., et al. (SNO Collaboration). (2002). Direct evidence for neutrino flavor transformation from neutral-current interactions in the Sudbury Neutrino Observatory. Physical Review Letters, 89(1), 011301.