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Lesson 1 celestial bodies

The celestial body is anybody swims in the space such as stars, planets, moons and rocky or gaseous bodies.

Stars: - When you look at the sky in a clear maples night, you will see a huge number of bright bodies called “Stars”

Stars

They are big-sized bodies emit enormous amounts of heat and light.

Stars appear small although they are big-sized, because they are millions of kilometers away from us.

The dist between the stars are very large, so astronomers don’t measure them by kilometers, but with the “ Light year”

Light year It is the distance covered by light in one year

and it equals 9.467× 1012 km.

What is meant by: The distance between the Sun and a star is three light years?

This means that the distance between the sun and this star = 3×9.467×1012 =28.401×1012km.

Ex: Calculate the distance in light year between two stars, if the distance between them equals 37.868×1012km.

Distance = = 4 light years

Star form groups called “Galaxies”

Galaxies

They are the grand (bigger) units forming this universe.

They are a tremendous collection of stars.

They are system that consists of thousands of millions of stars.

The galaxy system that our Solar system belongs to it is known as “the way of chopped hay galaxy” القَشِّ المُقَطَّعِ" or “The milky way galaxy” الطريق اللبنى"

Milky Way galaxy takes an oval shape with coiled spiral arms extend from it, the sun lies on one of these spiral arms.

Solar System

Through the astronomical expedition, astronomers knew the solar system.

The sun

It is the star of our solar system

It is the biggest body in the solar system

The planets

- They are eight spherical opaque bodies revolve around the sun in one direction (counter clock wise) ضد اتجاه عقارب الساعة

They revolve around the sun in semi- circular or elliptical (oval) paths (orbits).

The paths of planets lie in one plane perpendicular to the Sun’s axis of rotation rotation around itself

The planets of the solar system are divided into two groups according to their distances from the Sun:

The inner planets group (the nearest to the Sun).

The outer planets group (The farthest planets from the Sun).

The small or inner planets group

They are the nearest four planets to the Sun in the solar system.

They are arranged according to their distances from the Sun (begin from the nearest) as follows: Mercury, Venus, Earth and Mars.

Characteristics خصائص of the inner planets:

They are small bodies, so they are called small planets.

They have a solid surface. (all of them have an atmosphere except Mercury).

Their densities are high (ranging between 3.3 to 5.5 gm/cm.3)

They have a few numbers of moons rotating around them except Mercury and Venus which have no moons.

Notice

Earth is the planet that we live on it and it is the highest density in the inner planets.

The nearest two planets to the Earth are Venus and Mars?

The big or outer planets group

They are the farthest four planets from the Sun in the solar system.

They are arranged according to their distances from the Sun (begin from the nearest) as follows: Jupiter, Saturn, Uranus and Neptune.

Characteristics of the outer planets:

1- They are big so they are called giant عملاقةَplanets.

2- They are gaseous bodies that are formed of gaseous elements

(the most important of them are the hydrogen and helium).

-Hydrogen gas is present in a solid state on the surface of outer planets(G.R)

Due to the high pressure and extreme coldness on the surfaces of these planets.

3- Their densities are low (ranging from 0.7to 1.3gm/cm)

Because they consist of gaseous elements.

4-They have large number of moons rotating around each of them.

The difference of Gravity force on the planets, surfaces

Isaac Newton attributed the falling of an apple on his head to the gravitational force of the Earth (which causes the Falling of that apple)

Then he proved that there is attraction force among objects in the space depends on:

The mass of each object.

The distance between them.

So, the planets revolve around the Sun in fixed orbits by the action of the Sun s gravitational force on them.

The gravitational force on the surface of the planets are variable as shown in the following table :

|Planet |Force of gravity the surface (m/s2) |

|Mercury |3.78 |

|Venus |8.60 |

|Earth |9.78 |

|Mars |3.72 |

|Jupiter |22.88 |

|Saturn |9.05 |

|Uranus |7.77 |

|Neptune |11.00 |

Comparison between the inner planets and the outer planets

|Points of Comparison |The inner planets |The outer planets |

|Definition |They are nearest four planets to the sun |They are farthest four planets to the sun |

|Their arrangement from the sun |Mercury, Venus, Earth and Mars |Jupiter, Saturn, Uranus and Neptune. |

|Size |Small in size |Big in size |

|Density |High |low |

|No . of moons |A few number of moons |Large number of moons |

| |Mercury and Venus have no moons | |

The moon

They are small planets

|Planet |No. of Moons |

|Mercury |- |

|Venus |- |

|Earth |1 |

|Mars |2 |

|Jupiter |22 |

|Saturn |60 |

|Uranus |27 |

|Neptune |12 |

that are affected by

gravity of the larger

planets and rotate around them

Asteroids الكويكبات

They are celestial bodies of thousands of different sized rocky masses that rotate around the Sun in a certain region called “the belt of the wanderer asteroids " which lies between the orbits of mars and Jupiter .

The belt of the Wanderer asteroids حزام كويكباتِ السيارة

It is a region separates the group of the inner planets from the group of the outer planets.

Meteors النيازك

When small rocky masses fall within the atmosphere of the Earth, they could burn up completely as a result of the heat produced from their friction with air forming luminous arrows in the sky.

These objects are called meteors.

Meteors can be seen with the naked eye at the clear nights.

Meteorites النيازك

When large rocky masses Fall within the atmosphere of the Earth and did not burn up completely, some parts of them which are called meteorites reach to the Earth s surface.

The biggest meteorite till now has a mass of 80 tons and exists at the southern west of Africa.

Comets المذنبات

-They are masses of rocks, ice and solidified gases.

- They revolve around the Sun in more elongated elliptical orbits intersecting with the orbits of the planets.

- The comet consists of two parts which are:

1- The head It contains:

Icy spheres which are a mixture of solidified gases (carbon dioxide nitrogen and methane gases).

Rocky parts.

Dust and water molecules.

2- The tail it is considered a gaseous cloud.

- The most famous comet is Hilly which completes its revolution around the Sun each 76 years.

Astronomers discovered the celestial by instruments called Telescopes

The Function of telescope

- It is used in identifying the celestial bodies.

The Kinds of telescopes

Reflecting telescope Refracting telescope.

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Discovering the celestial bodies

Meteorites:

The remaining part of the rocky masses without burning that falls on the surface of the Earth.

They are luminous arrows that can be seen in the sky.

Meteors

Notice

- Saturn planet has the large number of moons revolving around it.

Notice

- Jupiter is the biggest planet in the solar system.

-Mercury is the nearest planet to the Sun , while Neptune is the Farthest one from the sun.

[pic]

[pic]

37.868×1012

9.467×1012

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