Model daily and yearly patterns of Earth and the sky

Learning goal: Use Earth's rotation and revolution to explain predictable day/night and sky patterns, then test a prediction with repeated observations. Rotation is Earth turning on its axis. Revolution is Earth traveling around the Sun. They occur together but explain different time scales.

Earth turns approximately once in twenty-four hours relative to the daily Sun cycle. At any time, the side facing sunlight has day and the side facing away has night, apart from twilight near the boundary. As Earth rotates, a place such as Ohio moves into and out of sunlight each day. The Sun does not need to orbit Earth once per day to explain this pattern. Places far to the north are an exception at some times of year: north of the Arctic Circle the Sun does not set around June 21 and does not rise around December 21, and at the North Pole there are about six months of continuous daylight and six months of continuous night. That pattern comes from the tilt of Earth's axis, named later in this lesson.

Use a globe and a stationary lamp in a dim classroom. Mark one location on the globe and turn the globe while keeping its center in place. Observe the marker entering the lit region, facing the lamp and moving into darkness. Keep the lamp fixed for the rotation demonstration so that the model tests Earth's turning rather than several changing motions at once.

Earth's rotation makes the Sun, the Moon and the stars appear to move generally from east toward west over a day or night. The Moon rises in the east and sets in the west for this reason, not because it circles Earth once a night. Its own orbit around Earth is much slower and shifts its position only a little from one night to the next. Some stars near a celestial pole appear to circle that region without rising and setting for a given observer. Polaris is close enough to the north celestial pole to appear nearly fixed compared with surrounding stars. Do not claim that every star follows an identical visible path from every location on Earth.

Shadows provide an indirect way to track the Sun's apparent motion without looking at it. An upright stick's shadow points away from the Sun's direction. With a fixed stick on a level surface, mark its tip and time repeatedly. A higher Sun generally produces a shorter shadow for the same stick; a lower Sun produces a longer shadow. Record direction as well as length.

Keep the stick vertical and the observation location unchanged. Clouds, a moving base or an uneven surface can complicate a record. Clock noon need not equal the moment of the day's highest Sun, so find the shortest observed shadow from the evidence rather than forcing it to occur at 12:00. Do not infer precise directions from an unlabeled classroom diagram.

Earth takes approximately 365 days to complete a revolution around the Sun. As its orbital position changes, the nighttime side faces different directions into space. Consequently, different constellations can be visible during nighttime at different portions of the year. Stars lying in the same sky direction as the bright Sun are difficult to see in daytime; they have not disappeared from space.

The orbit model shows Earth at two opposite positions. At one position, the midnight side faces outward in one direction; roughly half an orbit later, it faces outward in the opposite direction. The outward arrows point toward distant star regions beyond the drawing. Those stars are not a small wall immediately surrounding the solar system, and the diagram does not represent actual star distances.

Earth's axis is tilted about 23.5 degrees from perpendicular to its orbital plane. This lesson names that feature but focuses on rotation, revolution and observable sky patterns. Detailed explanations of seasons and changing daylight duration require additional work. A daily shadow record alone does not demonstrate all yearly changes, and one night's star view cannot establish a full annual cycle.

Worked prediction: If an Ohio observation marker on a globe turns from the lit side into the dark side, it models the transition toward night. Moving the entire globe around the lamp would instead model revolution and should not be used as the daily cause.

Worked record critique: A group measures a shadow at 9 a.m., moves the stick indoors, then measures beside a different building at noon. The changed setup prevents a clean comparison. Keep the same vertical stick and location, note weather and repeat observations across the day.

Guided investigation: With adult supervision, mark a fixed stick's shadow at several times on a suitable day, measuring length and compass direction without looking at the Sun. Keep weather notes and repeat on another day when possible. Alternatively use a clearly labeled simulation and state that its data are simulated.

Independent performance: Demonstrate rotation and revolution separately, explain an observed shadow pattern and use a location-appropriate sky chart to compare nighttime views several months apart. Identify what is predictable, what data are missing and which model features are not to scale. Retain actual dated observations or simulation settings as evidence.

Source references: National Snow and Ice Data Center, Arctic Weather and Climate, https://nsidc.org/learn/parts-cryosphere/arctic-weather-and-climate (polar daylight and darkness). Consulted October 1, 2026.