SCIENCE EARTH and SPACE Intermediate
People once thought that the sun moved around the Earth. After all, the sun seems to rise in the east and set in the west.
Today we know that the Earth rotates, or spins, not the sun. This spinning causes day and night. It is the reason that the sun seems to rise, move across the sky, and then set.
Have you ever been on a merry-go-round? It turns around a pole in its center. Earth is like a giant merry-go-round, but the pole is imaginary. This imaginary pole is called Earth’s axis.
Rotation is counterclockwise when viewed from the North Pole. How long does it take for the Earth to complete one full rotation?
South Pole The axis runs through Earth’s center, from the North Pole to the South Pole. Earth rotates on its axis once about every 24 hours.
22.5 South Pole The axis is not at a 90 degree angle. The Earth’s axis is tipped over at an angle of 22.5 degrees. This is why we experience seasons.
As Earth rotates, only one side of it faces the sun. This part of Earth is having daytime. The other side of the Earth faces away from the sun and is having nighttime. As the Earth rotates, we have day and night over and over again and again.
What is responsible for Americans having daytime while it is nighttime in Australia?
The time it takes a planet to rotate once on its axis is 1 full day. The rate of rotation is different for each planet, so each planet has a different number of hours in one of its days. One Earth day = 24 hours.
E W The Earth rotates on its axis from WEST to EAST. It takes 24 hours for the Earth to make one complete rotation on its axis.
As the Earth continually rotates on its axis, tilted over at about 23 degrees, it is also moving in another way. It is revolving. To revolve is to follow a path around the sun.
Earth takes about 365 days to make one complete orbit around the sun. As Earth moves around the sun, Earth’s axis stays tilted in the same direction. The tilt of Earth’s axis plus its orbit causes the seasons.
N The path that the Earth travels on is called its orbit. Earth’s orbit around the sun follows the same path.
But not every planet has the same number of hours in their day. Some planets have shorter days while others have longer days. The amount of time it takes the planet to complete one full rotation determines the length of each planet’s day.
Earth is divided into halves called hemispheres. The upper half is the Northern Hemisphere. The lower half is called the Southern Hemisphere.
The hemispheres are divided into halves by the imaginary line called the Equator. Equa = Equal Hemi = Half
There is also the Western Hemisphere and the Eastern Hemisphere. The Earth is cut in half from North to South.
Because of the tilt of the Earth, the Northern Hemispheres is tilted toward the sun during the summer months and gets more rays of sunlight. There are also more hours of daylight and it’s warmer. Summer is here.
When it is summer in the Northern Hemisphere, the opposite season is occurring in the Southern Hemisphere. The Southern Hemisphere is tilted away from the sun and gets less sunlight. There are fewer hours of daylight, and it’s cooler. It is winter.
In December, the Northern Hemisphere is tilted away from the sun. It’s winter now. At the same time, the Southern Hemisphere is tilted toward the sun. Now it’s summer in the Southern Hemisphere.
PATTERNS in the SKY For thousands of years, people have seen pictures in the stars. They connect the stars to make a pattern or a shape. This is the Big Dipper.
Star patterns are called constellations. Constellations are groups of stars that seem to form a pattern in the night sky. The early Greeks named constellations after animals or people from stories called myths.
The Big Dipper is part of a constellation called Ursa Major, or The Great Bear. Orion is a constellation named after a hunter in a Greek myth.
As Earth rotates on its axis, constellations seem to move across the night sky. Like the sun, constellations seem to rise in the east and set in the west. Stars above the North Pole, don’t seem to move as much. They move in a circle.
The positions of the constellations seem to change with the seasons. This is because we see different parts of space as Earth revolves around the sun. Stars do change over time, but it will take millions of years for a constellation to change its shape.
Show What You Know Day and night are caused by Earth’s ______________________. 2. Earth revolves around the sun once every _____________________. 3. Earth’s seasons are caused by Earth’s revolution and _____________. During winter in the Northern Hemisphere, there are ___________ ____________ and it is _____________. 5. When it is spring in the Northern Hemisphere, it is ______________ in the Southern Hemisphere. 6. Constellations appear to move across the night sky because of Earth’s ___________________________.
Earth Earth number 3 - Earth the perfect home for me! M-V-E-M-J-S-U-N (P - Little Pluto doesn’t count any more )
MERCURY Mercury is the closest planet to our sun. It’s only 36 million miles from our sun. Mercury orbits the sun every 88 days and spins or rotates on its axis every 59 days.
Mercury is the smallest planet in our Solar System. It is about the size of our moon. Mercury has no moons or natural satellites of its own. There is very little atmosphere because of the limited gravitational force. The gravitational force is about 1/3 of Earth.
Mercury is extremely hot during the day because it is so close to the sun. It can reach 450 degrees C ( 840 degrees F) during the day and then plummet to -170 degrees C ( -275 degrees F) at night. Mercury is very similar to Earth in composition. It has a very rocky surface and an iron core.
MERCURY Roman god of commerce, travel and thievery Mercury Mercury number 1! Mercury closest to the sun.
VENUS Venus is the 2nd planet from our sun. It is located between Mercury and Earth, about 47 million miles from our sun. Venus orbits the sun every 225 days. It spins or rotates on its axis around the sun every 243 days. So each day is longer than its year.
Venus rotates east to west instead of west to east, like on Earth. Venus is called our “sister planet” because it is almost the same size as Earth. Venus has no natural satellites or moons. The atmosphere is 95% carbon dioxide. There is no magnetic field on Venus.
Venus is covered with thick clouds which hold in the heat. (greenhouse effect) Temperatures range from about 500 degrees C (900 degrees F) to -32 degrees C (-50 degrees F). Venus has a rocky, waterless surface with mountains, canyons, plains, and a 200 -mile long river of hardened lava.
VENUS Roman god of love and beauty Venus Venus number 2. Too hot for me – too hot for you!
EARTH Earth is the 3rd planet from our sun. It is located 93 million miles from the sun. Earth orbits our sun about every 365 days, travelling at more than 67,000 mph. Earth spins or rotates on its axis every 24 hours.
Earth 5th largest of all the planets. It has one natural satellite, our moon. The atmosphere is gaseous consisting of 78% nitrogen and 21% oxygen. Earth’s gravity is 9.8 meters per second squared. Strong enough to keep us from floating away.
Over 71% of Earth is covered in water! Allowing life to flourish. The coldest temperature ever recorded was 89 degrees C (-128 degrees F). The hottest temperature was 58 degrees C ( 136 degrees F).