1 Earth, Moon, and Sun Earth, Moon, and Sun
2 Astronomy The study of the moon, starts, and other objects in space.The ancient Egyptians were among the first people to study the stars. They watched the sky to predict floods, and to be prepared to plow and plant their fields
3 How Earth Moves Earth moves through space in two major ways: rotation and revolution. The sun and moon seem to move across the sky each day because Earth is rotating on its own axis.
4 Rotation The imaginary line that passes through the Earth’s center and the North and South poles is Earth’s axis. The spinning of Earth on its axis is called rotation This causes day and night. As Earth rotates, the part of it facing the sun experiences day, and the part of it on the opposite side experiences night. It takes Earth about 24 hours to rotate once, hence one day being 24 hours long.
5 Revolution In addition to rotating on its axis, Earth also travels around the sun. Revolution is the movement of one object around another. One complete revolution of the Earth around the sun is called one year. Earth’s orbit, or path, is not quite circular, it’s an ellipse.
6 The Seasons of Earth Most places on Earth (besides the poles and tropics) have 4 seasons: winter, spring, summer, and autumn. The temperatures differ from place to place, though. Sunlight hits the Earth’s surface most directly at the Equator, which is why it’s warmest there. Sunlight hits the poles at a steeper angle, causing it to spread out over a greater area, which is why the poles are cooler.
7 Earth’s Tilted Axis and SeasonsEarth has seasons because its axis is tilted as it revolves around the sun. Otherwise, temperatures would remain the same all year long. Earth’s axis is always tilted at an angle of 23.5° from vertical. As it rotates, the North pole faces the sun for part of the year, and away from the sun for part. Distance from the sun does not cause seasons.
8 Earth in June North end of axis is tilted toward the sunIn the Northern Hemisphere, there are more hours of daylight than darkness. It is summer because of direct sunlight and more hours of it, which heats the Earth’s surface more than any other time.
9 Earth in December People in the Southern Hemisphere receive the most direct sunlight. Sun’s rays in the Northern Hemisphere are more slanted and there are fewer hours of sunlight. It is winter.
10 Solstices The days when the sun is farthest north or south of the equator. Summer solstice for us is when the sun is farthest north of the equator, around June 21st. Longest day of the year for our hemisphere. Winter solstice for us is when the sun is farthest south of the equator, around December 21st. Shortest day of the year for our hemisphere.
11 Equinoxes Twice a year when day and night are each 12 hours long (light and dark) everywhere on Earth. Equinox means “equal night.” Vernal (spring) Equinox – around March 21st, marks the beginning of spring in the northern hemisphere Autumnal Equinox – around September 22nd, marks the beginning of fall in the northern hemisphere
12 Gravity and Motion In 1666, when an apple fell from a tree, Isaac Newton first thought about the moon’s orbit and theorized that there must be a force between the Earth and moon to keep the moon in orbit.
13 Gravity Force – a push or a pullMost everyday forces require objects to be in contact. Gravity is different. Gravity – a force that attracts all objects toward each other. Law of Universal Gravitation – Newton’s law which states that every object in the universe attracts every other object. The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.
14 Gravity, Mass, and WeightWhy don’t you feel objects pulling you? Mass – the amount of matter in an object does not change Weight – the force of gravity on an object can change depending on its location On the moon, you would weight about 1/6 of your weight on Earth. This is because the moon is much less massive than Earth, therefore the moon’s gravity on you is far less than that of Earth’s gravity.
15 Gravity and Distance The strength of gravity is affected by the distance between two objects as well as their masses. The force of gravity decreases rapidly as distance increases. If the distance between two objects were doubled, the force of gravity between them would decrease to ¼ of its original value.
16 Inertia and Orbital MotionInertia – the tendency of an object to resist a change in motion. The more mass an object has, the greater its inertia. An object with greater inertia is more difficult to start or stop. Newton’s First Law of Motion – an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unless acted upon by a force.
17 Orbital Motion Newton concluded that two factors – inertia and gravity – combine to keep Earth in orbit around the sun and the moon in orbit around Earth.
18 Motions of the Moon The “near side” of the moon always faces the Earth, the “far side” always faces away. As the moon revolves around Earth, the relative positions of the moon, Earth, and sun change. The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides.
19 Phases of the Moon The moon does not produce light – it reflects light from the sun. This is why we can see it. The different shapes of the moon you see from Earth are called phases. The moon goes through its whole set of phases each time it makes a complete revolution around Earth. Phases are caused by changes in the relative positions of the moon, Earth, and sun. *the half of the moon that faces Earth is not always the half that is sunlit*
20 Phases of the Moon, cont’d.The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth. About 29.5 days after the last new moon, the cycle is complete, and a new moon occurs again.
21 Eclipses When the moon’s shadow hits Earth or Earth’s shadow hits the moon, an eclipse occurs. Most months, this does not happen! Eclipse – occurs when an object in space comes between the sun and a third object, casting a shadow on that object
22 Solar Eclipses Solar Eclipse – occurs when the moon passes directly between Earth and the sun, blocking sunlight from Earth. A new moon blocks our view of the sun
23 Total Solar Eclipse Umbra – the very darkest part of the moon’s shadow, which is cone-shaped. From any point in the umbra, light from the sun is completely blocked by the moon. The point of the umbra reaches only a small part of Earth’s surface. People within the umbra experience a total solar eclipse. For a short time, the sky turns dark and eerie as night – even in the middle of a clear day – and the air cools. You can see the stars and the solar corona, the faint outer atmosphere of the sun.
24 Partial Solar Eclipse Penumbra – another shadow cast by the moon that is less dark than the umbra, and much larger. In the penumbra, part of the sun is visible from Earth. In a solar eclipse, people in the penumbra see only a partial eclipse. An extremely bright part of the sun remains visible, making it dangerous to look at.
25 Lunar Eclipses Lunar Eclipse – occurs at a full moon when Earth is directly between the moon and sun. Earth blocks sunlight from reading the moon.
26 Total Lunar Eclipse Like the moon’s shadow in a solar eclipse, the Earth also has an umbra and penumbra. When the moon is in Earth’s umbra, you see a total lunar eclipse. Can be seen anywhere on Earth that the moon is visible. The edge of Earth’s shadow is visible before and after a lunar eclipse.
27 Partial Lunar Eclipse Occurs when the moon passes partly into the umbra of Earth’s shadow. The edge of the umbra appears blurry, and you can watch it pass across the moon for or 3 hours.
28 Tides Tides – the rise and fall of ocean water that occurs every 12.5 hours or so. Water rises for about six hours, then falls for about six hours, in a regular cycle. The force of gravity pulls the moon and Earth (including the water on Earth’s surface) toward each other. Tides are caused mainly by differences in how much the moon’s gravity pulls on different parts of Earth.
29 *see Tides handout, it’s more clear there!*The Tide Cycle The moon’s gravity causes high tide on the side closest to the moon The moon’s gravity pulls on Earth more strongly than it does on the water on Earth’s opposite side, therefore causing high tide on the opposite side of Earth, as well. Between the areas of high tides, water flows away, causing low tides. *see Tides handout, it’s more clear there!*
30 Spring Tides The gravity of the sun and the moon pull in the same direction. Their combined forces produce a tide with the greatest difference between consecutive low and high tides, called a spring tide.
31 Spring Tides The sun’s gravity also pulls on the Earth’s waters.During a new moon, the Earth, moon, and sun are nearly in line. The gravities of the sun and moon pull in the same direction, producing the highest difference between high and low tides, called a spring tide. Occurs twice per month, at a new and full moon.
32 Neap Tide During the moon’s first-quarter and third-quarter phases, the sun and moon are at right angles (90°) to Earth. The sun and moon pull at right angles, causing a neap tide, which has the least difference between high and low tides. These occur twice per month.
33 Earth’s Moon Until 1609, no one knew anything about the moon. They could see the shapes on it, but couldn’t explain them. Telescope - a device build to observe distant objects by making them appear closer 1609, Galileo Galilei made his own telescope and was able to see much more detail about the moon than anyone had seen before. He was that the moon had an irregular surface, not smooth as the Greeks thought previously.
34 The Moon’s Surface We know much more now than Galileo knew!Features on the moon’s surface include: Maria Craters Highlands
35 Maria Galileo named the dark, flat areas of the moon’s surface maria, the Latin word for “sea,” after incorrectly thinking they were oceans. Maria are actually hardened rock formed from huge lava flows between 3 and 4 billion years ago.
36 Craters Galileo saw that the moon’s surface is marked by large round pits, or craters. Some craters are hundreds of kilometers across! Scientists mistakenly thought that craters were made by volcanoes – they weren’t. The craters were caused by the impacts of meteoroids, chunks of rock or dust from space. Maria don’t have as many craters as the rest of the moon’s surface, suggesting the craters formed before the maria did.
37 Highlands Some of the light-colored features on the moon’s surface are highlands, or mountains. The lunar highlands cover much of the moon’s surface.
38 Characteristics of the MoonAlthough Earth’s closest neighbor is the moon, it’s quite different from Earth. The moon is dry and airless, small compared to Earth, and has large variations in its surface temperature. Size and Density The moon’s diameter is a little less than the distance across the U.S. The moon has 1/8 as much mass as Earth. The moon has a dense core, but less dense outer layers.
39 Characteristics of the Moon cont’d.Temperature and Atmosphere Temperatures range from 130°C (266°F) in direct sunlight to -180°C (-292°F) at night. The temperatures range so much because the moon has no atmosphere and the gravity is so weak that gases easily escape into space. Water There is no liquid water on the moon, but there may be large patches of ice near the moon’s poles. Some areas are shielded from sunlight by crater walls. Temps in these areas are so low that ice would remain frozen.
40 The Origin of the Moon The best-fitting theory of the moon’s origin is called the collision-ring theory. About 4.5 billion years ago, the solar system was full of rocky debris, some the size of small planets. Scientists theorize that a planet-sized object collided with Earth to form the moon. Material from the object and Earth’s outer layers was ejected into orbit around Earth, where it formed a ring. Gravity caused the material to combine to form the moon.
41 Traveling into Space Rocket – a device that expels gas in one direction to move in the opposite direction. The first rockets were made in China in the 1100s Modern rockets were first developed in the early 1900s by Russian and American physicists. Rocket design made major advances during World War II, when Germans used a rocket called the V2 to destroy both civilian and military targers.
42 How do Rockets Work? A rocket moves forward when gases shooting out the back of the rocket push it in the opposite direction. Action and Reaction Forces Basic physics law: For every force or action, there is an equal and opposite force or reaction. Thrust – the reaction force that propels a rocket forward. Amount of thrust depends on mass and speed of gases propelled out of the rocket. Greater thrust, greater velocity. Velocity – the speed in any given direction.
43 Orbital and Escape VelocityOrbital Velocity – the velocity a rocket must achieve to establish an orbit around Earth. If a rocket moves slower than orbital velocity, Earth’s gravity will cause it to fall back to the surface. Escape Velocity – the velocity a rocket must reach to fly beyond a planet’s gravitational pull A rocket with a velocity of 40,200 km/hr or more can escape Earth’s gravity and fly off into space.
44 Multistage Rockets The idea of multistage rockets was proposed in 1903. The main advantage of a multistage rocket is that the total weight of the rocket is greatly reduced as the rocket rises. Smaller rockets, or stages, are placed one on top of the other and fired in succession. In the 1960s, multistage rockets, such as the Saturn V made it possible to send spacecraft to the moon and the solar system beyond. Today, multistage rockets are used to launch a variety of satellites and space probes.
45 Multistage Rocket Demonstration
46 The Race for Space In the 1950s, the U.S. and the Soviet Union (Russia) began to compete in space exploration, called the “space race”. At the time, the Soviet Union was the greatest rival to the U.S. in politics and military power – Cold War. In 1957, the Soviets launced a satellite, Sputnik I, into orbit.
47 First Artificial SatelliteSatellite – an object that revolves around another object in space. The moon is a natural satellite of Earth. A space craft orbiting Earth is an artificial satellite. Sputnik I is an example of this. Soviet success in satellite launching caused alarm for the U.S. U.S. responded in 1958, launching the Explorer I into orbit. Over the next few years, both countries launched more! Late 1958 – U.S. created National Aeronautics and Space Administration (NASA), a government agency in charge of space program.
48 Humans in Space 1961 – space race heated up!Soviets launched the first human into space. Yuri Gagarin flew one orbit around Earth aboard Vostok 1. Less than one month later, Alan Shepard became the first American in space aboard Freedom 7. First American to orbit Earth – John Glenn in 1962, aboard Friendship 7. Spacecraft he traveled in was called a space capsule because it was like a small cap on the end of the rocket The capsule orbited Earth three times.
49 Missions to the Moon May 1961 – President John F. Kennedy launched an enormous program of space exploration & scientific research Apollo program was the American effort to land astronauts on the moon. Unpiloted U.S. spacecraft Surveyor landed on the moon and did not sink, proving the moon had a solid surface.
50 The Moon Landings July 1969 – 3 American astronauts aboard Apollo 11 circled the moon. Buzz Aldrin & Neil Armstrong entered the tiny spacecraft, Eagle, and on July 20 landed on the Sea of Tranquility, a flat area on the moon’s surface.
51 Exploring Space Today Space Shuttles – spacecrafts that an carry a crew into space, return to Earth, and then be reused for the same purpose. Before 1983, spacecraft could only be used once. NASA has used space shuttles to perform many important tasks, such as: taking satellites into orbit, repairing damaged satellites, and carrying astronauts to and from space stations.
52 Space Stations Space Station – a large artificial satellite on which people can live and work for long periods. A space station provides a place where long-term observations and experiments can be carried out in space. In the 1970s and 1980s, both the U.S. and Soviet Union placed space stations in orbit. In the 1980s, the U.S. and 15 other countries began planning the construction of the International Space Station. 1998 – first section placed into orbit. Since then, many other modules have been added on.
53 Space Probes Space Probe – a spacecraft that carries scientific instruments that can collect data, but has no human crew Space probes gather data about distant parts of the solar system where humans cannot easily travel. Each probe is designed for a specific mission. Some probes are designed to land on certain planets Some probes are designed to fly by and collect data Each probe has a power system to produce electricity, a communication system to send and receive signals, and scientific instruments to collect data or perform experiments.
54 Space Probes, cont’d The scientific instruments that a probe contains depend on the probe’s mission. Some are equipped to photograph and analyze the atmosphere of a planet. Others are equipped to land on a planet and analyze the materials on its surface. Some probes have small robots called rovers that move around on the surface A rover typically has instruments that collect and analyze soil and rock samples.