Lesson 17 – Things you need to know but they are not on the reference table.

The Universe The universe consists of everything in space. The universe was created in an explosion called the Big Bang. The universe is expanding in all directions. The universe contains countless number of galaxies. A galaxy is a cluster of billions of stars. We live in a spiral galaxy called the Milky Way galaxy.

Stars Stars are big balls of hydrogen gas that has ignited and creates a large amount of energy. Stars use hydrogen as a fuel for a special nuclear reaction called a fission reaction. During a fission reaction, stars combine 2 hydrogen atoms to create a helium atom. If a star has more hydrogen than helium, the star is said to be a young star. If a star has more helium than hydrogen, the star is said to be an old star. Stars start out as large clouds of gas called nebula. Gravity pulls the gas atoms together until they form a ball and ignite. When star use up all their hydrogen, they die. They die in two ways: They explode into a nova Collapse into a black hole.

Earth’s Motions - Revolution The Earth revolve around the Sun. We know this because we see different constellations throughout the year. The Earth moves about 1 degree each day as it travels on it orbit. The Earth's orbit is not a circle, but more like an oval; and the Sun is not in the center of the oval, but more to one side. During its travels around the Sun, the Earth is sometimes close to the Sun and far away from the Sun. As the Earth moves closer to the Sun, it speeds up. As the Earth moves from the Sun, it slows down.

Earth’s Motions - Rotation The Earth spins on it axis. We know this because of three factors: Star Trail – When photographing the night sky, stars leave streak marks of the film. These marks tend to move in a circular motion at about 15 degrees per hour. Fulcrum – A fulcrum is a device that a weight tied to the end of a string and is allowed to swing. The swinging of the weight will create a straight line; but as the day move on, the fulcrum will change direction and completing a star shape design. The coriolis effect – The coriolis effect is cause objects to curve slightly as they are moving in a straight line. Objects, like wind and water, in the northern hemisphere will curve in a counterclockwise direction; while things in the southern hemisphere will curve clockwise. . The Earth rotates at a speed of 15 degrees per hour.

Polaris Polaris, also known as the North Star, sits directly over the North pole. (It never moves) Polaris can only be seen in the northern hemisphere. Polaris’ altitude is the same as the latitude that someone is observing it from. Example: if Polaris is at a height of 35 degrees, then the person is standing at 35 degrees North latitude. Polaris is at zero degrees (the horizon) at the equator and 90 degrees at the north pole. As you travel north, Polaris rises in altitude. Polaris is the only star that doesn’t move across the night sky. All the star travel around it.

The Seasons The Earth is on a permanent tilt of about 23.5 degrees. The North Pole is always pointing to Polaris (the North Star) as the Earth travels around the Sun. Because of the tilt and the way the North Pole points to Polaris, there are times where the northern hemisphere is getting more sunlight then southern hemisphere, and vice versa. This uneven distribution of sunlight across the northern and southern hemisphere cause the seasons to occur. When the North Pole is facing the Sun, the northern hemisphere is getting more sunlight than the southern hemisphere. This is summer in the northern hemisphere and winter in the southern hemisphere. When the North Pole is facing away from the Sun, the northern hemisphere is getting less sunlight than the southern hemisphere. This is winter in the northern hemisphere and summer in the southern hemisphere. Draw the diagram – Note the why the north pole is pointing to and way from the sun and the shading of the shadow.

The Sun’s movement across the sky The Sun always rises in the East and Sets in the West, however the path is not always the same each day. In the Summer, the sun rises in the North-East and sets in the North-West. This is the longest path the Sun will take during the year, so there will be more hours of sunlight. (June 22) In the Winter, the sun rises in the South-East and sets in the South-West. This is the shortest path the Sun will take during the year, so there will be less hours of sunlight. (December 22) In the Spring and Fall, the sun rises in the East and sets in the West. This is the middle path the Sun takes twice a year, so there will be equal hours of sunlight. (September 22 and March 22)

The Sun’s movement across the sky and shadow lengths A shadow is created when an object blocks the pathway of light. A shadow will always point in the opposite direction from the light source. During the morning, a shadow of a tree or building will shrink as the Sun approached Noon. At noon, the Sun will be at its highest point and the shadow will be at its shortest. As the Sun moves from noon to sunset, the shadow will grow. At sunrise and sunset, the sun is at its lowest and the shadow is at its longest. During the winter months, the Sun is traveling on its shortest and lowest path, so the shadows will be their longest throughout the day. During the summer months, the Sun is traveling on its longest and highest path, so the shadows will be their shortest throughout the day.

Note the shadow length for each seasons.

Angle of Isolation The angle of isolation refers to the angle in which light wave hit the Earth. When the Sun is directly overhead, noon or during the summer months, the light waves are hitting the ground at a steep angle. This also means that more light waves are hitting the ground at the same time. This causes the ground to heat up more. That is why noon time and summer tend to be warm times. When the Sun is at a low angle in the sky, sunrise/sunset or during the winter months, the light waves are hitting the ground at a gradual angle. This also means that less light waves are hitting the ground at the same time. This causes the ground to heat up slowly. That is why the morning/ sunset and winter tend to be cool times. The higher the angle of the sun, the higher the angle of isolation, the warmer it is.

The Moon The Moon is revolving around the Earth every 27.3 days; however, because the Earth is also revolving around the Sun, it takes 29 days for the moon to go from full moon to full moon. Like the planets in our solar system, the moon orbits the Earth in a counterclockwise direction. The Moon rotates at the same speed as it revolves (27.3 days). That is why we always see the same side of the Moon throughout the month. As the moon travels around the Earth, different parts of the Moon receive light and darkness. The proportion of dark and light we see is known as the phases of the Moon.

Draw and copy.

The Moon In the New Moon, the moon is between the Earth and the Sun; we see only darkness. In the Full Moon, the moon is behind the Earth and furthest from the Sun; we see 100% light. It takes roughly 14 days for the Moon to travel from the New Moon phase to the Full Moon phase.

Eclipse An eclipse is when an object is blocked out by a shadow. For Earth Science this blockage deals with the positions of the Moon, Earth and Sun. There are two types of eclipses: A Solar Eclipse – when the Moon blocks out the Sun. This only occurs during the New Moon phase The position is Earth, Moon, Sun Lunar Eclipse – when the Moon moves into the Earth’s shadow. This only occurs during the Full Moon phase The position is Moon, Earth Sun

Tides Tides are the periodic rising and lowering of oceans. Tides are predictable (roughly 6 hours between low to high, & 12 hours between low to low or high to high) Tides occur as the results of gravitational pull from the Moon and the Sun. Both the Moon and the Sun affect the tides: The Sun is very big and has a lot of gravity, but it is far away so it gravitational effects are small. The moon is small but close to the Earth, so its gravitational effects are big Tides occur 4 times a day. 2 High Tides and 2 low tides. High tides occur when the Moon is directly overhead and directly on the opposite side of the Earth. Low tides occur when the Moon is perpendicular to that side. During New and Full Moons, the high tide is at its highest because the Earth, Moon and Sun are in a straight line; so both the Moon and the Sun are pulling in the same direction.