Download 1st.Prep.Unit _3_ lesson_1_

*stares:
They are big sized bodies emit enormous amounts of heat & light.
They are a huge number & the distance between them very large so we measure them by light year.
*light year:
It is the distance covered by light in one year.
Light year= 9.467x10 12km
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*Galaxies:
They are grand (bigger) units forming universe. OR They are tremendous collection of stars. OR They are a system
of thousands of millions of stars.
*Milky way galaxy:
Spiral arms extend from it when sun (solar system) lies on one spiral arm.
*Telescopes:
Used to discover celestial bodies
Two types: (Reflection telescope & Refraction telescope).
*Solar system:
Consists of: 1)-Sun
2)-Plants
3)-Moons (natural satellites)
4)-Other celestial bodies.
1-Sun:
It is the star in solar system. OR It is the biggest body in solar
system. OR It lies in the center of solar system & all bodies revolve
around it.
2- Planets:
They are eight spherical opaque bodies revolve around sun in one direction.
1-Inner
2-Outer
1-They are nearest four planets to sun.
2-Mercury, Venus, Earth& Mars.
3-Small in size
4-Structure: rocky components.
5-High density.
6-Afew number of moons rotate around them
earth (one moon)& mars (two) but mercury and
Venus have no moons
7-they have small gravitational force.
1-they are farthest four planets from sun.
2-Jupiter, Saturn, Uranus& Neptune.
3-Big in size
4-Solidified gases.
5-low density
6-they have large number of moons.
7-they have large gravitational force.
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3-Moons:
They are small planets (satellites) affected by the gravity of larger planets & rotate around them.
4- Other celestial bodies:
1-Asteriods:
They are rocky bodies rotate around sun in region of belt of wanderer asteroids
*-Belt of wanderer asteroids: It is the region separates the group of inner & outer planets.
2-Meteors:
They are luminous arrows that can be seen in sky due to completely burning of small rocky masses in earth
’s atmosphere.
3-Meteorites:
They are the remaining part of big rocky masses without burning that fall on earth ’s surface.
4-Comets:
They are masses of rocks, ice and solidified gases that revolve around sun in more elongated elliptical
orbits intersecting with orbits of planets.
*-Consists of:
1-head: Contains icy spheres that mixture of solidified gases (nitrogen, carbon dioxide& methan gases), rocky parts &
Dust and water molecules.
2-tail: Gaseous cloud.
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