SCIENCE COURSE: 7th. GRADE.
PROF. LIRIETT HERRERA
APRIL 20, 2012
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“There are no walls at the edge of this universe...
Absence of gravity is the limit of space existence”.
Toba Beta
UNIT IOBJECTIVES
•To identify the different types of celestial bodies.
•To discover what a star is and how we can
•distinguish one star from another.
•To learn about the different shapes of galaxies.
To know the Solar System and its components
UNIT I
The celestial bodies in the universe are very diverse
•. Here we have a list of celestial bodies from our universe:
•Planets: Like the Earth, which is the planet we live on.
•Satellites: Like the Moon, which is the Earth’s natural satellite.
•Comets: Which orbit the Sun on a very long trajectory.
•Asteroids: Rocky bodies which are smaller than planets, •very often irregular in shape, and which orbit around the Sun.
•Stars: Like the Sun which continuously radiate energy into the space around them.
•Galaxies: Groups of tens or hundreds of thousands of stars.
• The Universe contains approximately 100,000 galaxies.
Cluster of Galaxies: Made up of many different galaxies
The Stars
If we look at the night sky on a clear night, we can see
hundreds of small lights which seem to be twinkling. These
are the stars.
If we look more closely we can see that some of the stars
seem to form groups. These are constellations. The best
known constellations are: Ursa Major, and Ursa Minor,
Orion, Leo and Pegasus, etc.
Different types of stars
Stars have different characteristics:
•Colour: When we look at the stars through binoculars or even with
the naked eye we can see different tones in different stars. Some
are blush, reddish, orange, and so on. The Sun is a yellow star.
•Size: The Sun is a medium- sized star. Betelgeuse, a star in the
constellation of Orion, is 600 times bigger than a Sun. On the other
hand, Sirius B in the constellation of Canis Major is 100 times
smaller than the Sun.
•Brightness: Some stars are brighter than others. Sirius is very
bright. Other stars are so faint that we cannot see them with the
naked eye. They have been discovered thanks to the use of
telescopes.
•Light: Some stars emit more light than others. Two stars
emitting the same amount of light will not be as bright as each
other if they are at different distances from the Earth.
Groups of stars
The Sun has no other star in its immediate surroundings, but this is unusual. It is more common to find stars in groups.
•The Binary Star System: These are two stars that turn around a common centre point.
•Cluster Star System: These are groups of tens, hundreds or thousands of stars.
The Galaxies
Galaxies are made up of groups of stars, gases and
dust (small solid particles).
Our galaxy is called the Milky Way. The nearest
galaxy to our own is Andromeda which is more than
two million light years away.
This means that when we look at this galaxy we are
seeing it as it was more than two million years ago.
Shapes of Galaxies
Elliptical: More or less spherical
Spiral: A flat disc, with several arms coming out of the nucleus of the spiral.
Irregular: With no specific shape.
The Solar System
We have already seen that there are different types of
celestial bodies in the Solar System.
The Sun is the central body. It is a Star. The planets,
their satellites, comets and asteroids revolve around
the Sun.
The planets revolve around the Sun in practically circular
orbits.
The planets which are farthest away revolve more slowly and
take longer to complete a full revolution
Rocky planets and gaseous planets
The planets can be classified into two different groups: the rocky planets and the gaseous planets.
Mercury, Venus and the Earth, Mars and Pluto are rocky planets. They have a solid surface.
Jupiter, Saturn, Uranus and Neptune are all gaseous planets. They do not have a solid surface.
PLANET DISTANCE FROM
THE SUN
PERIOD OF
ROTATION
PERIOD OF
REVOLUTION
Mercury 0.39 58.65 days 88 days
Venus 0.72 243 days 224.6 days
Earth 1.00 23 h 56 min 365.25 days
Mars 1.52 24 h 37 min 1.88 years
Jupiter 5.20 9 h 55 min 11.86 years
Saturn 9.54 10h 40 min 29.46 years
Uranus 19.19 17 h 14 min 84.07 years
Neptune 30.06 16 h 7 min 164.82 years
Pluto 39.44 6 38 days 274.70 years
The planets in the Solar System