2. “There are no walls at the edge of this
universe...
Absence of gravity is the limit of space
.
existence”.
Toba Beta
3. UNIT I
UNIT I
OBJECTIVES
•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
4. The celestial bodies in the universe are very diverse
•. Here we have a list of celestial bodies from our universe:
5. •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
6. 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.
7. 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.
8. •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.
9. 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.
10. 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.
11. 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.
12. 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
13. 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.
14. The planets in the Solar System
PLANET DISTANCE FROM PERIOD OF PERIOD OF
THE SUN ROTATION 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
