Complex sentence: It is the most northerly circle of latitude on the Earth at which the Sun is directly overhead at noon on the Northern solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent.
Split into simpler sentences: It is the most northerly circle of latitude on the Earth at which the Sun can be directly overhead. This occurs on the Northern solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent.