The Sun

Sol, or the Sun, was the home star of the solar system, a planetary system about twenty-seven thousand light years from the galactic centre of Mutter's Spiral.

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 spacial cartography system. (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's 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)

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) 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)

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)

Soare