Treasure three-ball instrument _600 words

The three-ball instrument on my desk was a birthday present from my father when I was in grade one. It is also a DIY product, which needs to be built by yourself.

The earth, the moon and the sun are all mounted on a tripod. 24 solar terms is marked below the sun, and the first quarter moon, the second quarter moon, the solar eclipse and the lunar eclipse are marked below the moon. There is a tray below, and there is a lever on the tray. At the other end of the lever, there are seven gears linked with each other. When I turn the minimum gear, the "earth" will start to turn slowly like a turtle. At this time, the place where the sun shines is daytime, and the other side is night. Therefore, there are days and nights on our earth. It takes about 24 hours for the earth to rotate once, which is one day. When I turn the gear under the moon, the moon will slowly revolve around the earth. At this time, the earth will keep rotating around the sun for one year, and at the same time, the solar terms are constantly changing all year round. There is also an angle between the sun and the earth. When I aim the pointer at 0 degrees, it is the vernal equinox, the summer solstice is 90 degrees, the autumn equinox is 180 degrees, and the winter solstice is 270 degrees, so there are four seasons in a year. The earth, the sun and the moon in our real life don't need to swing manually like my tripod, but are constantly moving. They rotate day after day and year after year. When the earth revolves around the sun, it doesn't swing from east to west like a gyro rotates on the ground, but always keeps its axis of rotation pointing somewhere, and its northern end always points to the north pole in the sky. My treasured three-ball instrument not only lets me know the relationship between the earth, the sun and the four seasons, but also understands the changing rules of the four seasons. It is also a very beautiful ornament!

Grade three: Wang Jinglin.