Santar was a planet in the Salgorax-Neptor system, just outside the Ortadd galaxy in the the galaxy's Alpha or Beta Quadrant. It is the site of a Human colony.
In 2265, the coronas of Salgorax and Neptor produced synchronous solar flares that formed a fiery arch. The spectacle was witnessed safely on Santar by inhabitants wearing darkened glasses.
During the flare, the Federation starship USS Enterprise was orbiting Santar. James T. Kirk and Spock beamed down to meet the colonial governor, but the flares misdirected the transporter beam to the planet Muton in the adjacent star system. Kirk and Spock returned to Santar aboard a transport. (TOS comic: "Slaves of the Frogmen")