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