The Moving Earth

Rotation and Revolution The way the Earth moves is the main factor that determines the way objects move in the sky. -The Earth’s rotation is its daily trip around its axis. -The Earth’s revolution is its yearly trip around the Sun. The following are determined based on our rotation: -day and night -length of shadows -stars apparent movement across the sky The following are determined based on our revolution: -seasons -visible constellations

Constellations A constellation is a group of stars that forms a pattern in the night sky. An asterism, The Big Dipper, is part of a constellation. There are a total of 88 recognized constellations. The constellations in the Northern Hemisphere received their names mainly from Greek and Roman mythology. Leo, Pisces, and Taurus were named for a lion, fish, and bull. Constellations started out as pictures in the minds of early people, much like seeing castles and dragons in the clouds. Now, they serve as a more useful tool. They provide us with a map of the sky. Constellations divide up the sky into 88 sections, which allow astronomers to locate things in the night sky. The star Betelgeuse, for example, can be found within the constellation Orion.

Constellation Video

Why do the Sun and the stars appear to move? Here’s an easy answer…they’re not moving, we are. The Earth is rotating on its axis as it revolves around the Sun. Ever spin around in a circle really fast? What is happening to the world around you? Is it really spinning, or does it just appear to be spinning? The Sun and the stars are acting in the same way. Notice the stars in the picture seem to be rotating around a center. At the center is the star Polaris, or the North Star. We call Polaris the “North Star” because the Earth’s northern axis always points towards it. Early sailors used this star to navigate their ships, since it was the only star that did not move across the sky.

Depending on the time of year, different constellations can be seen in the night sky. The 12 signs of the Zodiac can all be seen throughout the year, although at different times.

Length of Shadows The Earth’s rotation effects the Sun’s position in the sky. The Sun rises in the East and sets in the West. This movement across the sky effects the length of shadows. The sundial was an early instrument used to tell the time of day.

We have seasons because Earth’s axis is tilted at 23 degrees. When the northern hemisphere is tilting towards the Sun, the northern hemisphere is in summer and the southern hemisphere is in winter. When the northern hemisphere is tilted away from the Sun, the southern hemisphere is in summer and the northern hemisphere is in winter.

Seasons When Earth is tilted towards the Sun, like during summer, the Sun appears higher in the sky and the days are longer. In the winter, the Sun is lower in the sky and is there for less time. The summer solstice is on July 21st and is the longest day of the year. The winter solstice is on December 21st and is the shortest day of the year. There are two equinoxes. The autumnal equinox is around Sept. 21st and the spring equinox is around March 21st.

The Moving Earth