The Nentir Vale
This dim red star shines high in the sky during three quarters of the year, only dipping down near the hoizon for the summer months. It only vanishes from sight completely for two weeks surrounding the longest night of the year.
Legend says that Hadar was once much brighter, and that during the clash of the tiefling empire of Bael Tureth and the dragonborn empire of Arkhosia the star blazed so intensely in the sky that it was painful to look at. When Bael Tureth fell, the star dimmed to its current state. It took over a century for astrologers to accept that it was still there. Up to that point, most argued that the red dot was simply a collective after-image of its previous brightness.
Hadar, the Ever-Hungry, aids warlocks who form pacts with him by allowing them to open small bits of him up upon the world, so that he may feed and regain strength.
The Warlock Hadarai, original member of the Eyes of Hadar and now the lord of the Chamber of Eyes, is one of those warlocks. His loyalty to this hungry star (alongside his goddess, the Raven Queen), contributed his name as part of the party’s moniker.