In an alternate Milky Way in an alternate universe, there is a cluster of stars so dense that nights are over 60 times brighter than our full moon. In that cluster is a solar system presented (albeit simplified) above. It is actually two separate binaries.
- The first one consists of a red giant 100 times as wide, one-third as massive and 1,000 times as bright as our sun orbited by a yellow-white dwarf 130% as wide, 170% as massive and six times as bright as our sun.
- The binary orbiting that binary consists of a yellow dwarf 105% as wide, 110% as massive and 126% as bright as our sun orbited by an orange dwarf 85% as wide, 78% as massive and only 40% as bright as our sun.
It is in the second binary that this alternate Earth orbits. With an axial tilt of only three degrees, the seasons are defined by how many suns are in the sky. "Summers" are when all four of them are present in the sky, making daylight as bright as Venus and nights 1,000 times brighter than back home. "Winters" are when only the two that it orbits can be seen, when daylight is as bright as our Earth and nights are more than 60 times brighter than back home.
An Earth like that sounds like good news for potential photosynthesizers, but there are problems with the parent binary. A red giant is big, obviously, which means that it had the potential to go supernova before long. And yellow-white dwarves can carry seven times more ultraviolet radiation than our sun. Put those two together, and you would have an alternate Earth that would have to orbit a secondary binary that orbits the primary binary from a safe enough distance.
So the question is--how far can the alternate Earth's binary orbit the primary binary without concern of near-future supernova or UV overdose?