Grade VIII- STARS AND THE SOLAR SYSTEM

STARS AND THE SOLAR SYSTEM

 

CELESTIAL OBJECTS:

The stars, the planets, the moon and many other objects in the outer space are called celestial objects.

 

GALAXIES:

Galaxy is a group of stars and other celestial bodies.

Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies.

• Spiral galaxies, such as the Milky Way, consist of a flat disk with a bulging center and surrounding spiral arms.
  
• Elliptical galaxies are shaped as their name suggests. They are generally round but stretch longer along one axis than along the other. They may be nearly circular or so elongated that they take on a cigarlike appearance.
  
• Galaxies that are not spiral or elliptical are called irregular galaxies. Irregular galaxies appear misshapen and lack a distinct form, often because they are within the gravitational influence of other galaxies close by.
  

STAR:

A star is a dense cloud of hydrogen and helium gas contracting under its own gravitational pull. In all the stars hydrogen atoms are continuously converted into helium atoms and this process is accompanied by a large amount of energy. This energy is radiated in the form of heat and light.

Reaction which takes place inside a star is nuclear fusion reaction

 

Why the stars appear to move from east to west?

The stars appear to move from east to west as the Earth rotates from west to east on its axis. A star which rises in the east in the evening sets in the west in the early morning.

 

Light year: It is the distance covered by light in one year.

1 Light year=9.46× 10¹²km

The nearest star to Sun, Proxima Centauri is 4.3 light years away.

In other words, its light takes 4.3 light years to reach us: we see it as it was 4.3 years ago.

 

PHASES OF MOON

The various shapes of the bright part of the moon as seen during a month are called phases of the moon.

 

 

 

 

 

 

 

 

 

 

 

 

What causes the different phases of the Moon?

The phases of the Moon depend on its position in relation to the sun and Earth. As the Moon makes its way around the Earth, we see the bright parts of the Moon's surface at different angles. These are called "phases" of the Moon.

 

New moon (or dark moon):

The new moon is seen when the moon and the sun are on the same side of Earth.

The moon is between the sun and the Earth. We see the side which is not lit, so the moon is dark.

 

Full moon

The Full Moon is when the Earth is between the sun and the moon.

 

 

The number of days between one new moon and the next new moon is days.

 

The moon goes through a complete moon phase's cycle in about one month. But it's not exactly one month. As seen by an observer on earth it is 29.5 days. If you were to view the moon cycling the earth from outside our solar system, the time required is 27.3 days, roughly two days less. This is because the earth is a moving platform.

 

SURFACE OF MOON:

The moon's surface is dusty and barren. The Moon has many mountains the low gravity of the Moon allows mountains to be very tall. The most "moonish" features of the Moon are its craters. These were caused when meteoroids or asteroids impacted onto the Moon.

 

 

Constellation:

A constellation is a group of stars that has a recognizable shape.

 

Ursa Major

Ursa Major is a constellation visible throughout the year in most of the northern hemisphere. Its name means the Great Bear in Latin.

 

How we can locate pole star?

Look at the two stars at the end of Ursa Major. Imagine a straight line passing through these stars. Extend this imaginary line towards the north direction. (About five times the distance between the two stars).This line will lead to the Pole Star.

 

 

 

 

 

 

ORION

Orion is very useful as an aid to locating other stars. By extending the line of the Belt southeastward, Sirius can be found

 

 

 

 

 

 

 

 

 

 

Meteoroids, Meteor & Meteorites

Little chunks of rock and debris in space are called meteoroids.

 

When meteoroid enters the atmosphere, air friction causes the body to heat up and emit light, thus forming a fireball, also known as a meteor or shooting star.

 

Meteoroids pieces that survive the journey and hit the ground are called meteorites.

 

COMET

Comets are cosmic snowballs of frozen gases, rock and dust. When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head. The dust and gases form a tail that stretches away from the Sun for millions of kilometers.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ASTEROIDS

In a belt between the orbits of Mars and Jupiter, millions of small irregular rocky bodies revolve around the sun. These are asteroids also known as minor planets.

 

SOLAR SYSTEM

Our solar system is made up of a star - the Sun - eight planets, moons, a bunch of comets, asteroids and space rocks, ice and several dwarf planets, such as Pluto. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

 

Remember the order of the planets like this:
My Very Educated Mother Just Showed Us Neptune.

The planets in our solar system can be divided into two groups. The innermost four planets—Mercury, Venus, Earth, and Mars—are small, rocky worlds. They are called the terrestrial (earthlike) planets. Earth is the largest terrestrial planet.

The outer four planets—Jupiter, Saturn, Uranus, and Neptune—are called gas giants or Jovian (Jupiter like) planets. They have gaseous atmospheres and no solid surfaces. All four Jovian planets consist mainly of hydrogen and helium.

 

 

 

Why Venus is hottest planet of our Solar system?

Venus has an extremely dense atmosphere, which consists mainly of carbon dioxide. The enormously CO₂-rich atmosphere, along with thick clouds of sulfur dioxide, generates the strongest greenhouse effect in the solar system, making Venus hottest planet of our solar system.

 

Venus is so much brighter than any other planet viewed in the sky. Why is it so bright?

70% of the light that hits Venus is reflected back into space. There are droplets of sulfuric acid and acidic crystals in the atmosphere of Venus. The smooth surfaces of these droplets of sulfuric acid and crystals reflect light very well, which is one reason why Venus is so bright. 

 

According to International Astronomical Union (IAU)

(1) A "planet" is a celestial body that

(a) is in orbit around the Sun,

(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes nearly round shape, and

(c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that

(a) is in orbit around the Sun,

(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape,

(c) has not cleared the neighbourhood around its orbit, and

(d) is not a satellite.

 

Artificial Satellite

An artificial satellite is an object which has been placed into orbit by human endeavor.

Geostationary and Polar Orbiting satellites:

1. Geostationary satellites are positioned at an exact height above the earth. At this height they rotate around the earth at the same speed as the earth rotates around its axis, so in effect remaining stationary above a point on the earth.
   

   As they remain stationary they are ideal for use as communications satellites and also for remote imaging as they can repeatedly scan the same points on the earth beneath them.
   

2. Polar Orbiting satellites by comparison have a much lower orbit, moving around the earth fairly rapidly, and scanning different areas of the earth at relatively infrequent periods.
   

Uses of different types of satellites:

1. Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects
   
2. Communications satellites are satellites stationed in space for the purpose of telecommunications.
   
3. Navigational satellites are enable mobile receivers on the ground to determine their exact location
   
4. Earth observation satellites are satellites intended for non-military uses such as environmental monitoring, meteorology, map making etc
   
5. Weather satellites are primarily used to monitor Earth's weather and climate
   
6. Scientific Research Satellite (commercial and noncommercial)
   

   Scientific research satellites provide us with meteorological information, land survey data (e.g., remote sensing), and other different scientific research applications such as earth science, marine science, and atmospheric research
   

   
    

VISiT

http://science.nationalgeographic.com/science/space/solar-system.html

http://solarsystem.nasa.gov/planets/

Ch11-FORCE AND PRESSURE

Force:
A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction
Force has both direction and magnitude.
SI unit of force is newton (N)

Effects of Force:
a) Force can make a stationary object move.
b) Force can stop a moving object.
c) Force can change the direction of a moving object.
d) Force can change speed of a moving object.
e) Force can change the shape of an object.

There are Two Type of Forces:

Contact Forces - involve physical contact between objects.
Examples: the force involved in kicking a ball, pulling a wagon, compressing a
spring, etc

Action-at-a-distance force- doesn’t involve physical contact between two interacting objects.
Examples: the gravitational force and the electromagnetic force
Gravitational force is the weakest force among all forces existing in nature. It is also
the easiest to observe, because it acts on all matter and it is always attractive.

Examples of Contact and Action-at-a-Distance Forces:
Contact Forces
a) Muscular Force
b) Normal Force, Air Resistance Force
c) Applied Force
d) Spring Force

e) Frictional Force

Action-at-a-Distance Forces

a) Gravitational Force
b) Electrostatic Force
c) Magnetic Force

Resultant/Net force acting on an object:
1. If forces applied on an object are in the same direction
Net force=addition of all forces

2. If forces applied on an object are in the opposite direction
Net force=difference of forces

Balanced Forces:
When forces acting on a body do not bring about any change in its state of motion, then the forces acting on the body are said to be balanced.
Net resultant force acting on body = zero
Unbalanced Forces:
When forces acting on a body bring about a change in its state of motion, then the forces acting on the body are said to be unbalanced.
Net resultant force acting on body is not equal to zero

Comparision between Balanced and Unbalanced Forces

Q. For each situation, determine the net force acting upon the object.

Q. The net force is known for each situation. However, the magnitudes of a few of the individual forces are not known. Analyze each situation individually and determine the magnitude of the unknown forces.

Contact Forces:
1. Muscular Force
The force resulting due to the action of muscles is known as the muscular force.
2. Friction
The force that tries to stop materials sliding across each other. Direction of frictional force is always opposite to the direction of motion.
Non-contact Forces:
1.Magnetic Force
Magnetic force is the force exerted by a magnet on another magnet or any magnetic material. Magnetic force can be either attractive or repulsive.
2. Electrostatic Force:
Some material becomes charged when they are rubbed. Their charge is called electrostatic charge.
The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.
3. Gravitational Force
If you hang an object from a spring balance, you measure a downward pull from the Earth.
This pull is called the force of gravity or just a gravitational force.
Main features of gravitational force
a) All masses attract each other
b) The greater the masses, the stronger the force.
c) The closer the masses, the stronger the force.

PRESSURE
Force (at right angles to a surface) acting on a unit area is called pressure.


Factors Effecting Pressure
1. Force: Pressure is directly proportional to force.
More the force, the more is the pressure and vice-versa 2. Area: Pressure is inversely proportional to the area
Lesser the area of contact, the more is the pressure and vice-versa.

Application of Pressure
1. Nails and pins have pointed ends
Nails and pins have very small are at the tips due to their pointed ends. A small force on the head of the pin or nail will exert considerable large pressure to drive pin into the surface easily.
2. Heavy trucks are fitted with six to eight wheels
Due to large number of wheels, the area of contact on the ground over which the weight of the heavy truck acts is increased. This reduces pressure exerted by the heavy truck on the ground.
3. Skiers use flat skies to slide over snow:
Skies have large area to reduce the pressure on the snow; enabling the skier to slide over the snow without sinking.
4. High rise buildings have wide foundations:
Wall foundations have a large horizontal area. This reduces the pressure underneath so that the walls do not sink further into the ground
5. Potters place a round piece of cloth on their head while carrying heavy load
By this they increase area of contact with their head. So, the pressure on their head is reduced and they find it easier to carry load.

PRESSURE EXERTED BY LIQUID
Liquids exert pressure due to distribution of their own weight.
Pressure in a liquid can be measured by a manometer.

* Water stream will start pouring out through the holes. This means that water is exerting pressure in all direction.
* In tin I, the water stream comes out evenly irrespective of the direction of the hole. This means that the pressure is equal at the same height or depth.
* In tin II and III, the water stream coming out of the lowest hole reaches the farthest. This shows that the pressure exerted by liquid increases with depth.
* Since there is no difference between the streams coming out of tins II and III, the pressure exerted by liquid is independent of the size of the container, but depends only on the height or the depth of the liquid.

Why base of dams are made broader?
When dams are built to stop and store water, it becomes necessary to make the base of the dam broader than the top. The base has to sustain greater pressure from the pressure of the water column as compared to the pressure exerted by the water on the surface.

ATMOSPHERIC PRESSURE
Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air above that surface.
In terms of air molecules, if the number of air molecules above a
surface increases, there are more molecules to exert a force on that surface and consequently, the pressure increases.
Atmospheric pressure is measured with an instrument called a "barometer".
Standard Atmospheric Pressure
1 atm=760 mmHg =101 300 Pa

If the area of my head were 10cm × 10cm, how much mass of air would I be carrying on my head?
At sea level the mass of air on 10cm × 10cm area is approximately equal to 1000kg.

Why we are not crushed by huge weight exerted by atmosphere on our body?
We aren’t crushed by huge atmospheric pressure because it is matched by the pressure in our lungs and blood system and cancels the pressure from outside.

Explain why, when you ‘suck’ on a straw, the liquid travels up it?
We expand our lungs to reduce the air pressure inside the straw. As a result atmospheric pressure pushes the liquid up the straw.