... M33: The Triangulum Galaxy . ... The spiral galaxy M33 is a mid-sized member of our Local Group of galaxies. M33 is also called the Triangulum Galaxy for the constellation in which it resides. ... Isaac Newton Explains the Solar System . ... But he went home from Cambridge one summer in 1665, thought a lot about the physical nature of the world, and came back two years later with a revolutionary understanding of mathematics, gravitation, and optics. Edmund Halley's Greatest Discoveries . ...