Earth Science: Earth Systems and Earth in Space and Time In the fourth grade students were introduced to the relationship between the sun, moon, and Earth. They have a general understanding how the visible shape of the moon defines a month and the spin of the Earth defines a day. Fifth grade students explore seasons and their relationship to the tilt of the Earth on its axis and revolution around the sun. They define a year as one revolution of the Earth around the sun, explain lunar and solar eclipses based on the relative positions of the sun, moon, and Earth and finally, the effect of the moon’s gravity on the ocean’s tides. Students study the universe beyond the sun, moon, and Earth and describe the position, motion, and relationship of the planets and other objects in the sky to the sun.