4.8C (S) - Science
Tides, Moon Phases and Seasons
- How do shadows change over time?
- Why does the Moon appear to change in appearance?
- What are tides?
- How often do tides occur?
- Why does the Earth have seasons?
- Why do day and night occur on Earth?
Tides are a phenomenon on Earth that occurs in a pattern that can be predicted. Tides are the rising and falling of sea levels every day. Most places near the ocean experience two high tides and two low tides every 24 hours.
Tides are caused by the pull of gravity – mostly from the moon. The moon’s gravity pulls water away from the Earth’s surface. This causes the water to rise, forming a bulge of water in the oceans. On the opposite side of Earth (away from the moon), the water is also pulled away from Earth’s surface forming another bulge. These bulges form high tides. The part of Earth closest to the moon usually has the highest tides.
Low tides occur where the water has been pulled away. The Sun’s gravity also influences the tides, but the moon has a greater effect than the Sun because the moon is so much closer to the Earth.
□ Some objects in the sky are only visible during daylight hours, others only during night time.
□ Day and night occurs every 24 hours.
□ The appearance of the Earth’s Moon changes over an approximately 29.5 day period.
□ The Moon has no light of its own; instead it reflects light from the Sun.
□ Shadows are shortest when the Sun is directly overhead.
□ Tides are caused by the gravitational pull of the Moon (and Sun).
□ Tides occur in patterns. Most places have two high tides and two low tides each day.
□ From high tide to high tide, takes about 12 ½ hours. From low tide to low tide, takes about 12 ½ hours.□ Earth’s seasons occur in a predictable pattern.
The Earth and the moon are partners in the solar system. The moon is the Earth’s only natural satellite. Because of its mass, Earth has strong gravity. This force keeps the moon from drifting off into space. The Earth and moon orbit the sun together and are alike in many ways, but Earth and its moon differ in many other ways. The moon looks much larger than the stars, but it isn’t. Its diameter, the distance from one side to the other, is only one-fourth of Earth’s, and it is much smaller than any star in the sky. Why does it look so large? The moon is closer to the Earth than any other space object.
The Earth orbits around the sun, while the moon orbits the Earth. Both the Earth and the moon rotate on an axis. The Earth rotates on its axis once every 24 hours (causing the day and night cycle) as it orbits the sun once every 365.25 days (1 year). The moon rotates on its axis as it orbits Earth. One rotation and one orbit of the moon around Earth take exactly the same amount of time, about 28 days. Because of this, the same side of the moon always faces the Earth.
The moon and the Earth are very much alike in one way: neither make their own light but instead receive all of their light from the sun. Even though it appears as the brightest object in the night sky, we would not be able to see the moon without the sun. The moon reflects, or bounces back, light from the sun like a giant mirror.
During each month, the moon seems to change shape, but it really doesn’t. It only looks like it changes shape because of the amount of the moon’s surface we can see from Earth. The changing views of the moon we see on Earth are called phases. The phases of the moon depend on its position in relation to the sun and Earth. As the moon makes its way around Earth, we see the bright parts of the moon’s surface at different angles. The phases of the moon gradually change until the cycle is complete and starts over. The illustration below shows some of the moon’s phases during one lunar cycle (about 28 days).
You are probably familiar with the pattern of the seasons. For example, you know that the Fourth of July occurs in summer every year. Most places on Earth experience four seasons— winter, spring, summer, and fall (or autumn). The seasons always occur in this order. Each season has its own characteristics. Winter is cold. The days are short and the nights are long. The sun does not rise very high in the sky. Summer is the opposite. The days are longer than the nights, and the sun is high in the sky. On one day in spring and one day in fall, the amount of daytime and the amount of nighttime are equal. There is 12 hours of each. These days are called the spring equinox and the
Living things respond to changes in the seasons. The leaves of many trees change colors and drop in fall. Some animals hibernate through winter. In spring, bare trees grow new leaves and flowers blossom. Many animals raise their young in spring and summer.
TICKET OUT THE DOOR
HINT THERE ARE 31 DAYS IN JANUARY