3rd and 4th grade Earth Science

4.E.2.1

Motions of the Earth, Sun and Moon

How Big is the Earth?

The Earth is the biggest of all the terrestrial planets. A terrestrial planet is a dense planet found in the inner Solar System. The diameter of Earth is 7,926 miles. The circumference measured around the equator is 24,901 miles. There are currently almost 7 billion people living on the Earth. About 30% of the Earth's surface is covered with land, while about 70% is covered by oceans.

The Planet

Our planet is an oasis of life in an otherwise desolate universe. The Earth's temperature, weather, atmosphere and many other factors are just right to keep us alive

Earth

In a way, the Earth is like a giant merry-go-round. Instead of giant friends pushing the Earth in circles, the Earth’s spin, or rotation was caused by forces during its creation. The Earth was formed amidst a giant cloud of dust and gas. Slowly over many millions of years this dust and gas slowly condensed under the force of its own gravity forming a small mass. As the mass grew larger and larger, so did the force of its gravity. As the young Earth’s gravity became more powerful, it began attracting dust and gas towards it at a faster rate. This caused a sort of traffic jam, as these materials raced towards the Earth. What resulted was a giant whirlpool like swirl of dust and gas. Consider what happens when you drain your bathtub. As the water all tries to rush down the drain at the same time, a circular funnel or whirlpool is created.

Earth’s Rotation

•The Earth is the third planet from the sun and it is the fifth largest planet in the solar system.

•The water bodies cover nearly 70 percent of the Earth's surface and the oceans are at least 4 kilometers deep.

•The Earth rotates around its own axis that tilts at around 23 ½ degrees. It is because of this angle of inclination of 23 ½ degrees that we have the four seasons.

•The planet Earth is around 4.5 to 4.6 billion years old and the oldest known living organism is less than 3.9 billion years old.

•It is the only planet in the solar system that has plate tectonics. The tectonic plates are regions that are floating on top of the magma of the Earth and can move against each other.

•The earth is not a perfect sphere but is slightly flattened at the north and south poles. Its shape can be described as an oblate spheroid and the Earth's rotation causes the central portion to bulge out.

•The internal temperature of the earth i.e. the Earth's core is as high as 7500 Kelvin, which is hotter than the surface of the sun.

•The core of the earth is surrounded by the mantle which has a thickness of 2900 kilometers.

Facts About Earth

Our Sun is not unique in the universe. It is a common middle-sized yellow star which scientists have named Sol, after the ancient Roman name. This is why our system of planets is called the Solar System. There are trillions of other stars in the universe just like it. Many of these stars have their own systems of planets, moons, asteroids, and comets.

The Sun was born in a vast cloud of gas and dust around 5 billion years ago. Indeed, these vast nebulae are the birth places of all stars. Over a period of many millions of years, this gas and dust began to fall into a common center under the force of its own gravity.

Sun

We don't often think of the Sun as having cooler areas on its surface. The Sun is far too hot for an astronaut to ever visit, but there are areas which are slightly cooler than others. These areas are known as sun spots. Sun spots are still very hot. However, because they are slightly cooler than the rest of the surface of the Sun, they appear slightly darker in color. The gravitational forces in Sun spots are also stronger than the other hotter areas. Of course, you cannot look directly at the Sun to see these spots because you would damage your eyes. Astronomers have to use special telescopes with filters and other instruments to be able to see the cooler spots on the surface of the Sun.

Sun spots come and go on a regular basis. At times, there are very few, if any sun spots. At other times there are far more. They generally increase in intensity and then decrease over a period of 11 years. This 11 year cycle is known as the Saros Cycle.

Sun Spots

~The sun is a star. ~The sun is the closest star to our

planet. Remember! ~The Earth orbits around the sun.~The sun is way bigger than the

Earth. ~DON’T TOUCH THE SUN! IT’S

HOT! The sun’s average surface temperature is 5700 C. Compare

that to the Earth’s average temperature, which is 20 C.

~The sun is 150 million km (93 million miles) away from the Earth.

~How old is the sun? Can you imagine 4.5 billion years?~We know that the Earth’s

structure consists of different layers. The sun also has layers but unlike the Earth, the sun is entirely gaseous; there is no solid surface.

~The sun rotates on its axis approximately once every 26

days. .

INTERESTING FACTS

ABOUT THE SUN

Luna is a beautiful world that lies some 384,400 kilometers (almost 239,000 miles) from Earth. It is littered with mountains, valleys, old volcano sites, and many bowl-like holes called craters. Luna is a neat world to explore because you can see it without a telescope or binoculars. I know you have seen it. In fact, you may even see it tonight, that is because Luna is our moon.

Moon

On July 20, 1969, American astronauts landed on the surface of the Moon in a spacecraft named the Apollo 11. Neil Armstrong was the first human being to step onto the surface of the Moon. This mission was followed by 5 more successful missions to land on the Moon. In total, 12 astronauts walked on the surface of the Moon from 1969 to 1972. The astronauts collected 382 kg (842 pounds) of rock samples from the moon during these missions. They conducted many scientific experiments also, including solar wind experiments, soil, magnetic field experiments, and many others. They were also able to travel around on the surface of the Moon in a rover vehicle that kind of looked like a dune buggy.

History About The Moon

~How long does it take the Moon to orbit the Earth? …..The Moon takes about 27 days (27 days, 7 hours, 43 minutes, 11.6 seconds) to go all the way around the Earth and return to its starting position.

~The Moon's orbit around the Earth is a slightly squashed circle called an ellipse.

~Whilst the Moon is orbiting the Earth, the Earth is constantly moving because it is orbiting the sun.

~How old is the Moon? …..The Moon is 4.5 billion years old.

~Which direction does the Moon travel around the Earth? …..Looking down from the north pole we would see the Moon orbiting counterclockwise from west to east.

It's probably easiest to understand the moon cycle in this order: new moon and full moon, first quarter and third quarter, and the phases in between.

As shown in the above diagram, the new moon occurs when the moon is positioned between the earth and sun. The three objects are in approximate alignment (why "approximate" is explained below). The entire illuminated portion of the moon is on the back side of the moon, the half that we cannot see.

At a full moon, the earth, moon, and sun are in approximate alignment, just as the new moon, but the moon is on the opposite side of the earth, so the entire sunlit part of the moon is facing us. The shadowed portion is entirely hidden from view.

The first quarter and third quarter moons (both often called a "half moon"), happen when the moon is at a 90 degree angle with respect to the earth and sun. So we are seeing exactly half of the moon illuminated and half in shadow.

Once you understand those four key moon phases, the phases between should be fairly easy to visualize, as the illuminated portion gradually transitions between them.

An easy way to remember and understand those "between" lunar phase names is by breaking out and defining 4 words: crescent, gibbous, waxing, and waning. The word crescent refers to the phases where the moon is less that half illuminated. The word gibbous refers to phases where the moon is more than half illuminated. Waxing essentially means "growing" or expanding in illumination, and waning means "shrinking" or decreasing in illumination.

Thus you can simply combine the two words to create the phase name, as follows:

After the new moon, the sunlit portion is increasing, but less than half, so it is waxing crescent. After the first quarter, the sunlit portion is still increasing, but now it is more than half, so it is waxing gibbous. After the full moon (maximum illumination), the light continually decreases. So the waning gibbous phase occurs next. Following the third quarter is the waning crescent, which wanes until the light is completely gone -- a new moon.

Phases Of The Moon

Waxing Crescent Moon Waxing Gibbous Moon

Waxing Moon

Waning Crescent Moon Waning Gibbous Moon

Waning Moon

First Quarter Moon Third Quarter Moon

Quarter Moon

Full moon is a lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun.

As seen from Earth, the hemisphere of the Moon that is facing the Earth (the near side) is almost fully illuminated by the Sun and appears round. Only during a full moon is the opposite hemisphere of the Moon, which is not visible from Earth (the far side), completely unilluminated.

Full Moon

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible from Earth during the night, when they are not obscured by atmospheric phenomena, appearing as a multitude of fixed luminous points because of their immense distance. Historically, the most prominent stars on the celestial sphere were grouped together into constellations and asterisms, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations.

Stars

So What Defines A Planet?

The International Astronomical Union defines a planet as a celestial body that orbits around a star (like our sun) and is big enough that it forms into a shape of a sphere by its own gravity. But a planet cannot be big enough that it can cause thermonuclear fusion. It also has to have a clear orbit with no other bodies of comparable size influencing its gravitational force.

Did You Know There Are Two Categories of Planets?

A Planet falls into two categories. It is either a Terrestrial Planet or a Gas Giant. Planets that have a body composed mainly of rock (like the Earth) is called a terrestrial planet. This would include Mercury, Venus, Mars and Earth. Gas Giants, however, are planets that are made of gas. They do not have a solid surface crust. Jupiter and Saturn falls into this category. Uranus and Neptune are also Gas Giants, but they also fall into sub category called Ice Giants because they contain a huge proportion of rock and ice as well.

Characteristics of the Planets

Appearance

Sun Mars Mercury

Venus

Earth

Jupiter

Saturn

Uranus

Neptune

Pluto

1,390,000

6,800 4,900 12,100 12,800 143,000 125,000 51,100 495,00 23,00

Size

***Measured in km

***Distance measured in Kilometers

Mercury 58 million

Venus 108 million

Earth 149.6 million

Mars 228 million

Jupiter 778.5 million

Saturn 1.43 billion

Uranus 2.88 billion

Neptune 4.5 billion

Pluto 4.98 billion

Average Distance From The Sun