The _____ divides the earth into the lit up part and the darkenenedpart?

Learn all this stuff; it'll be on your test. International Date Line: a line of longitude located in the Pacific Ocean that divides days. If it's 2 PM Tuesday on the west side of the IDL, then it's 3 PM Monday on the east side of the IDL.

Prime Meridian: this is 0 degrees longitude, and it runs through Greenwich, England. Every location to the east of this line is described as X-degrees East, and every location west of this line is described as X-degrees West.

Circle of Illunination: the dividing line between sunlight and night side

Arctic Circle: an area at the north end of the planet above an imaginary line called the Arctic Circle that encircles the planet. Everything north of the Arctic Circle is referred to generically as "The Arctic." It's cold up there. But at the center of it is Santa's Workshop.
the line dividing the light and dark area of globe is called the terminator