Astronomy lesson 3

2. Planets and Orbits
Do you know what is the meaning of the word
“Planet”?
It means “wanderer”
Solar System
It consists of a star as well as all the planets ,moons
and other bodies travelling around it

3. what keeps the planets revolve around the
sun without wandering in the outer space?
1)Gravity
• It is the force of attraction among all objects .
• Gravity causes something you drop to fall to the floor ,and this
same type of force keeps planets in orbits .

4. • The amount of gravitational force such as that between the
sun and a planet depends on mass.
• The greater the mass of each object is ,the greater the
attraction between them is
• Distance also is a gravitational factor ,the greater the
distance is between the planet and the Sun ,the smaller the
pull of gravity .

5. 2)Inertia
• It is the second property that keeps planet in its orbit .
• It is the tendency of a moving object to stay in motion .

6. • Gravity alone would pull the planets into the Sun
,because the sun has so much mass.
• This doesn’t happen because the planets have
“inertia”
• Inertia alone ,however would cause the planets to
move in straight line .
• The balance between inertia and force of gravity
keeps the planet in their orbits around the sun .

7. • The planet would move in straight line because of its
inertia ,but gravity pulls on the planets and curves
their paths into orbits around the Sun

8. Ancient Explanation
1) Earth is considered to be the center of
universe .
• According to this model ,the Sun ,the moon and the stars revolve around the
Earth

9. 2)The other explanation stated that earth the
moon,the stars and other planets revolve
around the Sun
•This idea better explained the motions of the
planets

10. Comets
• It is a ball of ice and rocks that orbits the Sun.
• As a comet approaches the sun ,the sunlight warms the comet ice
causing the ice to turn to gas forming a cloud of gases.
• Near the sun the radiations pushes the cloud away forming comet
tail which is always pointing away from the Sun .

11. Meteoroids
• They are small rocky or metallic objects that orbits the Sun.
• The craters on the moon where formed by meteoroids
collisions

12. Meteor
• It is a meteoroid that enters Earth’s atmosphere, it appears
as a bright streak in the sky .

13. Meteorite
•If a meteor fails to break apart and burn up in the
atmosphere it can hit Earth’s surface .
•A meteoroids that strikes Earth’s surface is a
meteorites