The Sun

Sol, or the Sun, was the home star of the solar system, a planetary system in Mutter's Spiral.

It was made up of 74% hydrogen and 24% helium, with trace elements comprising the star's remaining 2%. (AUDIO: Feast of Fear)

History
The First Doctor was unfamiliar with Sol prior to his departure on Gallifrey. However, his granddaughter Susan Foreman learned of the existence of the solar system and Earth in her spatial cartography lessons. (AUDIO: The Beginning)

When the Sun was a "young star", a scientist lured the Umbra to himself, having brought them together with his immense guilt. He then used what the Twelfth Doctor guessed was a trans-warp tunnel, using the Sun as a power source, to send the Umbra from the scientist's planet into the Sun, where they survived the heat and "swam" for many years through the chromosphere. Millions of years later, the quadrillionaire Rudy Zoom spent ten years planning his expedition to circumnavigate the Sun in the sunship the Pollyanna so that Rudy could become the first man on the Sun. After the Pollyanna entered the chromosphere, the Umbra attacked the ship and began killing and devouring the "souls" of the humans on board. With the help of Alice Dubrovnik's graviton inverter, the Polyanna was able to invert the gravity on board the Pollyanna "to the right degree" and also invert and "[p]ush[...] away" the heat — which also had mass and gravity — from the exterior of the Pollyanna. This caused the Umbra, whom the Doctor had lured to the Pollyanna's surface, to freeze to death. (COMIC: The Eye of Torment)

Stealing a prototype stellar manipulator, the Eleven concocted an ultimately unsuccessful plot to ignite Sol and destroy the solar system in 1639. (AUDIO: The Satanic Mill)

In the 2010s, Sol released a massive solar flare that threatened to wipe out all life on Earth which not even the Doctor's TARDIS detected at first. However, a massive forest that grew up over night shielded the planet from danger. (TV: In the Forest of the Night) In 2016, the Twelfth Doctor had Grant throw the Shoal spaceship into Sol to completely and harmlessly destroy the threat it posed. (TV: The Return of Doctor Mysterio)

In the 26th century, a group of fringe academics called the Helios Society believed that the sun contained a habitable paradise they dubbed Heliotopia. Dr Suleiman Zorn was the leader of the society and wrote a treatise on the Heliopian concept. They drove a starship, the SS Suria Namasca, towards the sun to that end, which the Fourth Doctor, Leela and K9 landed on when the Doctor's TARDIS needed to repair itself. (AUDIO: Shadow of the Sun)

For some time around 4009, Tent City was located inside Sol's photosphere. (PROSE: The Book of the Still)

Human scientists predicted solar flare activity would sterilise their homeworld of Earth and took measures to prepare for it. To this end, they left Earth in ships, amongst them Starship UK. (TV: The Beast Below) Space Station Nerva may have gone into service as a refuge for humans and other life in cryogenic suspension. (TV: The Ark in Space)

In the 57th segment of Time the last humans left on Earth evacuated the planet because of the increasing danger that it would fall into the Sun. They fled to planets such as Refusis II (TV: The Ark) and Frontios. (TV: Frontios) Some accounts indicate the Sun destroyed the planet in 10,000,000 (PROSE: The Book of the War, Of the City of the Saved...) or 12,000,000, (PROSE: The Brakespeare Voyage) but others indicate the now uninhabited Earth was preserved by the National Trust and over the billions of years following was restored to a "classic Earth" before it was finally destroyed by the expanding sun (TV: The End of the World) in the year 5,000,000,000. (TV: New Earth) According to yet another account, at a point when humans still inhabited the Earth, the Sun slowly imploded in a way which was visible from, and did not immediately destroy, the planet; this heralded "the end of the world". (PROSE: Assessment Day)

Some posthumans modified themselves into homo solarians and lived in the expanding Sun before it was eventually swallowed by Grandfather's Maw in 60,000,000,000. (PROSE: The Brakespeare Voyage)

Cultural and religious significance
In 100,000 BC, a tribe of early humans worshipped Sol as Orb. (TV: An Unearthly Child)

In Mexico circa the 15th century, the timing of a solar eclipse had great religious significance. (TV: The Aztecs)

By the time humanity had become a space-faring civilisation, the Apollonians worshipped the Sun as a god. According to Sandy Tanaka, the Apollonians had a prophecy, in which "[i]f the body of the Sun [were] ever violated, [...] 'the Eye of Torment' [would] open. It [would] look down on humanity and condemn [them]." (COMIC: The Eye of Torment)

Alternate timelines
In an alternate timeline where the creation of GENIEs brought the Earth to the brink of destruction, people used the sun to power the earliest created GENIE they could find so that it could travel back in time to the day of its creation. The sheer power destroyed the GENIE which could not withstand being powered by the sun itself. As the people planned, the lab and the research contained within was destroyed in the process, preventing widespread use of GENIEs and saving the Earth. (PROSE: The Stone Rose)

Parallel universes
In the first parallel universe that Rose Tyler visited while trying to find her way back to N-Space, Sol fell victim to the reality bomb, causing its version of Earth to freeze over. (AUDIO: The Endless Night) In the second, Earth's orbit had been shifted so that it was closer to Sol, triggering a constant rain, a situation suspected to have been caused by alien powers. (AUDIO: The Flood)

Sole Soare