In our solar system, nine planets circle around our Sun. The
Sun sits in the middle while the planets travel in circular
paths (called orbits) around it. These nine planets travel in
the same direction (counter- clockwise looking down from
the Sun's north pole).
Inner system contains Mercury, Venus, Earth and Mars. These
four planets are closest to Sun.
Outer system contains Jupiter, Saturn, Uranus, Neptune
The inner planets are separated from the outer planets by
the Asteroid Belt.
Day and night occur because of earths rotation. It turns
dark outside when the sun is on the other side of earth. All
of this happens during the 24 hour cycle.
How Days & Nights occur?
The seasons are caused by the tilt of the Earth's rotational axis away or
toward the sun as it travels through its year-long path around the sun.
The Earth has a tilt of 23.5 degrees relative to the "ecliptic plane" (the
imaginary surface formed by it's almost-circular path around the sun). The
tilt toward the sun is maximized during Northern Hemisphere summer in
late June (the "summer solstice"). At this time, the amount of sunlight
reaching the Northern Hemisphere is at a maximum.
In late December, on the date of the "winter solstice", the Earth's tilt away
from the sun is maximized, leading to a minimum of sunlight reaching the
Northern Hemisphere. The seasons, of course, are reversed in the Southern
How do seasons occur?
Time Zones are a geographical world globe division of
15o each, starting at Greenwich, in England, created to help
people know what time is it now in another part of the
What are Time zones?
Many of the objects you can see in the night sky are stars,
large objects in space that produce light. Stars are so far
away that their light does not reach us for years. As light
from so far away passes through our atmosphere, it is
moved around so that the star seems to twinkle.
What are stars?
A celestial body moving in an elliptical orbit around a star.
What are Planets?
Difference between stars & Planets
A star has its own light.
Stars twinkle at night.
The relative positions of the stars do
not undergo any noticeable change.
Since the stars are very far away, the
telescope can only make them look
brighter but not larger.
A star has very high temperature.
There are billions of stars in the
A planet has no light of its own. It shines by
reflecting the light of the sun.
Planets do not twinkle.
Since planets are very mush closer to the
earth than the stars are, their motion around
the sun is noticeable as a daily shifting of
their relative positions in the sky.
Most planets on the other hand are near
enough to the earth to be magnified by the
Planets have low temperatures.
There are only nine planets in the solar
Venus is covered in clouds.
These clouds are about 10 miles (16.5 km) thick and begin
about 50 miles (83 km) above the ground.
From the surface of a planet, clouds obscure sunlight.
From up above, however, they reflect sunlight very
Venus reflects about 60-80 percent of the sunlight it
Why do Venus shines?
The brightness of a star depends on its size , temperature
& its distance from the Earth.
Star Temperature Color Distance from
Sun 6000 Yellow 8 light min
Sirius 11000 White 8.6 light years
Arcturus 4000 Orange 36 light years
Betelgeuse 3000 Red 520 light years
Spica 25000 Blue 220 light years
Some well known Bright Stars
A group of stars forming a pattern that is traditionally
named after its apparent form or identified with a
mythological figure. For example Orion.
Moon: the Earth’s Satellite
A system of millions or billions of stars, together with gas
and dust, held together by gravitational attraction.
What is Galaxy?
There are billions of Galaxies in the Universe. Some are
very small with only a few million stars. While others could
have as many as 400 billion stars, or even more. There are
three kinds of Galaxies, Spiral, Elliptical, and Irregular. The
only difference between the three is what shape they are.
The three types of Galaxy
Our galaxy, the Milky Way, is typical: it has hundreds of
billions of stars, enough gas and dust to make billions more
stars, and at least ten times as much dark matter as all the
stars and gas put together. And it’s all held together by
gravity. Like more than two-thirds of the known galaxies,
the Milky Way has a spiral shape. At the centre of the
spiral, a lot of energy and, occasionally, vivid flare. are
being generated. Based on the immense gravity that
would be required explain the movement of stars and the
energy expelled, the astronomers conclude that the centre
of the Milky Way is a supermassive black hole.
Other galaxies have elliptical shapes, and a few have
unusual shapes like toothpicks or rings. The Hubble Ultra
Deep Field (HUDF) shows this diversity. Hubble observed a
tiny patch of sky (one-tenth the diameter of the moon) for
one million seconds (11.6 days) and found approximately
10,000 galaxies, of all sizes, shapes, and colours. From the
ground, we see very little in this spot, which is in the
After the Big Bang, the Universe was composed of
radiation and subatomic particles
The shapes of galaxies are influenced by their neighbours,
and, often, galaxies collide. The Milky Way is itself on
a collision course with our nearest neighbour, the
Andromeda galaxy. Even though it is the same age as the
Milky Way, Hubble observations reveal that the stars in
Andromeda's halo are much younger than those in the
Milky Way. From this and other evidence, astronomers
infer that Andromeda has already smashed into at least
one and maybe several other galaxies.