Stars and The Solar system

Introduction

Vast Space Filled With Stars

Where ever we see above to the sky a vast majority seems empty and in this space are dwindling natural bodies this unimaginable space is called universe. 

Sun and Family 

Or The vast unimaginable space whiche encompasses most distant stars, planets and anything else, which exists is called universe and the science which deals with it is called astronomy so we can say astronomy is the the study of universe.

Galaxy

When we see in the night sky we see little bright light points commonly called stars but what we see are not all stars but there are  planets ,satellites meteors etc too. During the day-time, we see a bright ball of fire in the sky which appears to move from the east to the west. We call it the sun.

At night, we see thousands of stars in the sky. If we watch the sky through a telescope we may see millions of stars, some of which are brightly coloured. We see certain groups of stars which appear to be in clusters. They are called constellations.

There is the moon whose size changes every day. The moon is a satellite of the earth which completes one revolution around the earth in 27.5 days. Furthermore,we see an occasional comet. It appears as a ball of fire, having a tail. Then, there are shooting starts or meteors. They appear to fall from the sky. In addition to it, there are planets like the morning stars.Bodies such as the earth, moon,planets, sun, stars, meteors, comets, etc are called heavenly or Celestial bodies.The description of all these are given below...

1. Universe : The sum of everything that exists in the cosmos i.e everything under consideration is called universe it is an entity or one component of a larger entity known as the multiverse. Some times space and time or all its contents is called universe.
2. Natural or Celestial body: It is defined as A natural occuring object which is located outside of Earth's atmosphere or space such as a comet, an asteroid, the Moon, a planet, the Sun, or a star.
3. Star: It is a luminous celestial body which is made up of plasma mainly hydrogen spherical in shape looking like a dot whose position is fixed  relative to other dots e.g sun. The largest known star is UY Scuti believed to be 1700 times larger than the sun ,the brightest star is Sirius A and B. The brightest star in the univers is Sirius, also known as the “Dog Star” or, more officially, Alpha Canis Majoris, for its position in the constellation Canis Major. Sirius is a binary star dominated by a luminous main sequence star, Sirius A, with an apparent magnitude of -1.46. The smallest known star is EBLM J0555-57Ab, the star is located some 600 light-years away in our Milky Way galaxy. Nearest star to our earth is the star Proxima Centauri. It is a companion star to the binary star system Alpha Centauri AB and is approx 4.2 light-years away from Earth.

1. Planet:  It is a non luminous celestial body which revolve around the star like seven planets of sun earth mercury etc. Each of the seven major bodies which move relative to the fixed stars in the night sky Mercury, Venus, the Sun, Mars, Jupiter and Saturn. 

Earth

Jupiter 

Mars

1. Stallite:  it is also a celestial body which revolves around the plant e.g Moon.The surface of the moon is rugged. Itis made of very large craters (deep depressions or holes) and very high mountains. It has no atmosphere, and hence, no life on it and Its gravitational pull is one sixth that the earth, same side of moon is facing  towards the earth. On the day side of the moon, the temperature could be as high as 110°C. On the contrary, the temperature on the night side of the moon could be as low as - 150°C.

Half Moon

Full Moon

1. Meteor: It is a fast-moving streak of light in the night sky believed to be caused by the entry of extraterrestrial matter into the earth's atmosphere; a shooting star or falling star. It is an atmospheric or meteorological phenomenon. These were sometimes classified as aerial or airy meteors (winds), aqueous or watery meteors (hydrometeors: clouds, rain, snow, hail, dew, frost), luminous meteors (rainbows and aurora), and igneous or fiery meteors (lightning and shooting stars). 
2. Meteorite: it is a metallic or stony object or body that is the remains of a meteoroid usually fallen on the earth's surface.
3. Comet: A small Solar System body consisting mainly of volatile ice, dust and particles of rock whose very eccentric solar orbit periodically brings it close enough to the Sun that the ice vaporises to form an atmosphere, or coma, which may be blown by the solar wind to produce a visible tail. Or Comets Are The bright "star-like", objects with along tail, approaching the sun in highly elliptical orbit are called comets.The bright star-like objects is commonly called the "head of the comet". It consists of frozen water, along with the sun, the ice and the gases along with dust change to form gaseous matter, which appear in the form of long tail. The tail of a comet always points away from the sun,because of the pressure of solar radiations (solar wind).The tail of the comets could be as long as 800 million kilometers.The time period of revolution of the comets around the sun is very long. There Are some comets which appear after fixed interval of time. Such comets are called periodic comets. Halley's Comet is one such periodic comet which is visible once in 76 years. It was sighted in 1910 and then in 1986. It is expected to visit us in the year 2062. Unlike planets, the comets do not last for ever in the solar system. It is because as they approach the sun, they lost a good amount of their mass in the form of gases and small chunks of rocks. At last they become smaller and smaller and finally disappear.

Astronomy

All we learnt above is taken the branch of science called astronomy and one who studies it is called astronomer or astronaut. It is said that NICHOLAS COPERNICUS is THE FATHER OF MODERN ASTRONOMY (1543-1943).

15.5.2 How do the Stars Emit Light?

All stars are giant balls of hydrogen

gas and this includes our sun which is a

medium star. At the core (centre) of this

giant hydrogen cloud, the temperature is usually  from 2 million to 5 million degree celsius, the hydrogen gas

fuses (joins or melts) to form a heavier gas

called helium, at that temperature with the liberation of a huge amount of heat and light energy and  it is this fusion of hydrogen gas within the core of the star which emits light energy.

The Sun

The sun is the nearest star from the

earth. Our sun is a medium order star in

terms of its mass and brightness. You may

wonder as to why the sun does not appear

like the other stars or why does it appear

bigger and hotter than other stars in the

sky?

Stars are always moving away from each

other at a very high speed.But when

viewed from the earth, the distance between them does not seem to change, because they are very far away from us. Hence, any change in the distance between them not become perceptible in few hun years.

 Why do the stars appear from east to west?

The earth rotates about its north-south axis from west to east. Thus due to relative motion, all heavenly bodies (stars, planets, moon), etc., appear to move from east to west.

How far is the nearest star

Alpha Centauri, from the earth.

The distance of the sun from the earth is 150 million kilometers. Whereas the distance of the nearest star (after sun) from the earth (Alpha Centauri) is 40678000 million kilometers. It is on account of these enormous distance that stars appear very small and appear to have much less heat and light as compared to the sun.

How big is the sun as compared

to earth?

The diameter of the sun is 1,400,000

km (approx). This diameter is 109 times the

diameter of the earth. Thus sun is

approximately 300,000 times heavier than

the earth.

What are Units of Measuring the

Distance of Stars from the Earth?

Most of the stars are so far away from the

earth, that even the light which travel at a

speed of 3 x 10³ km/s (300,000 km/s) takes

million of years to reach on the earth. Thus,

the distances of the stars are measured in

light years.

What is a Light Year?

The distance travelled by the light at a

speed of 300,000 km/s in one year (365

days) is called light year.

1 light year speed of light x 365 days

                  = 300,000 km/s x 365x24x60x60s

                  =9,460,000,000,000 km

                  = 9.46 x 10¹km

What is a Light Minute?

The distance travelled by the light at a

speed of 300,000 km/s in one minute (60

seconds) is called a light minute.

1 light minute = 300,000 km/s x 1 minute

                           = 300,000 km/s x 60s

                           = 18,000,000 km=18x 10⁰km

 How far is the nearest star

Alpha Centauri, from the earth in

kilometers ?

Alpha Centauri is at a distance of 4.3 light

years.

Therefore, Distance in kilometer - Distance

travelled in one light year x Number of light

years

= 9.46 x 10¹² km/light year x 4.3 light

=40.678 x 10¹km.

15.5.4.3 Why do the stars appear to us

like point objects?

years

The stars, much like our sun are

celestial bodies, which continuously emit

heat and light. Our sun is a medium sized

star but It appears bigger to us, because it is nearest to the earth. All the stars appear to us like points, because they are very far away from the earth. Most of the stars are so much far away, that the light from them

takes million of years to reach the earth.

 Appeared to be changed the distance between any two stars not change when viewed from the earth?

Stars are always moving away from each

other at a very high speed but when

viewed from the earth, the distance between them does not seem to change, because they are very far away from us. Hence, any change in the distance between them does not become perceptible in few hundreds of years.

15.5.4.5 Why do the stars appear to move

from east to west?

It is because the earth rotates about

its north-south axis from west to east. Thus due to relative motion, all heavenly bodies (stars, planets, moon), etc., appear to move from east to west.

15.5.4.6 Why does the pole star (Polarls

or Dhruva Tara) not change its position in

the sky?

The direction of the Pole star is situated 

which is directly above the geographic

north-pole of the earth's axis. Therefore the position relative to the earth does change and hence, it appears stationary.

Constellations

A group of stars which forms a recognisable

pattern or shape is called a constellation.

Astronomers have divided the whole

sky into 88 constellations. Each  constellation is assigned a name

object to which it closely resembles. In 

ancient Indian astronomy, the constellations were known as Nakashatras. A few of the

prominent constellations are discussed

below.

(1) Ursa Major or Big Dipper or Vrihat

Saptarishi

This constellation consists of 7 bright stars arranged in a pattern somewhat

resembling the shape of a big bear. The

stars marked 1, 2, 3 and 4 represent the

body and the stars marked 5, 6, and 7

represent the tail of the big bear. The head

and paws of the big bear are formed by

some faint stars, not shown in diagram.

Ursa Major

The Ursa Major constellation can be linked

to the following objects:

(i) It looks like an oversized ladle in which

stars marked 1, 2, 3, and 4 form the cup of

the ladle and stars marked 5,6 and 7 form

the handle.

The stars 1 and 2 at the end of the

cup of the ladle are called pointer stars, as

they point in the direction of the pole star.

(ii) It looks like a question mark suspended

across the sky, where the stars 1, 2, 3 and 4

form the curved path and the stars 5,6, and

7 straight line part of the question mark.

(iii) It resembles a kite having a long tail.

The Ursa Major is visible clearly in

the northern part of the sky in the summer

months, between April to September.

(2) Ursa Minor or Laghu Saptarishi or

Dhruva Matsaya Ursa Minor constellation is also a group of seven stars, similar to that of Ursa Major. However, the stars in Ursa Minor are closer and dimmer as compared to the stars of Ursa Major and  They form an outline of a kite or a  ladle. At the tail of Ursa Minor is a star of

average brightness. It is called pole star or

polaris. In Indian astronomy, the pole star is called Dhruva Tara. Ursa Minor is clearly

seen in northern sky in July in summer.

Ursa major

Polaris or Pole star

Pointer stars

Fig. 15.4 Relative Positions of Ursa Major and Ursa Minor.

How to locate the pole star?

Look straight in the direction of the stars

situated at the far end of the ladle in Ursa

Major (stars 1 and 2) and The star of medium brightness in the direction of the above stars is the pole star . These stars star 1 and 2 in Ursa Major which point in the direction of the pole star are called pointer stars.

(3) Orion or Hunter or Mriga or Vyadha

Orion is another constellation of 7

stars and is one of the most magnificent

constellations in the winter sky. Its name in Indian astronomy is Vyadha or Mriga. It

looks like a hunter with his shield and club

upraised (Fig. 15.5). The seven major stars in it form the body of the hunter. The head and limbs are formed by faint stars.

Phases of The Moon

The moon is a non-luminous body. It has no light of its own and  It only reflects the light of the sun falling on its surface. This reflected light reaches the earth and  we see the moon. The part of the moon which is visible, is that reflects the sunlight towards the earth.The New Moon day, the moon is between the sun and the earth and the reflected light from the moon does not reach the earth

and hence it is not visible, In a way, the dark side of the moon is facing us on New Moon day. But The night, just after the new moon day, we see the crescent Moon. It is because only the reflected light from the crescent part reaches the earth and The rest of the moon is only faintly visible, because the sunlight reflected from the earth also falls on the moon's disc.

The crescent goes on increasing

every day, till on the fifteenth day (from the

New Moon day), the full bright face of the

moon is visible but The earth is between the sun and the moon, such that

the night side of the earth is facing the day side of the moon. This is called Full Moon day. This gradual increase every day in the bright disc of the moon is called waxing of the moon.

 The bright face of the moon goes on decreasing every night After the Full Moon and this decrease in the bright disc of the moon is called waning of the moon. By another fifteen days, New Moon is formed. This waxing and waning of the disc of the moon, as the moon revolves around the earth is called phases of the moon. The moon revolves around the

earth. As the earth moves around the sun,

in the same way the moon revolves around the sun, along with the earth. The moon completes one revolution around the earth in 271 days. It takes exactly the same time to spin once about the axis. Due to the same time for rotation on its axis and revolution around the earth, it always presents the same face towards the earth. However, as the moon revolves

around the earth, the earth moves ahead in its own orbit around the sun. Thus, from the earth the moon appears to complete 

one revolution between one New Moon to next Moon in 291 ½ days. Lunar calendars

commonly used by astrologers are based

on the fact that the Moon completes one

revolution around the Earth in 29% days.

Test Yourself

1. Define celestial bodies? Name any

three celestial bodies.

2. Why do you classify the sun as a star?

3. Why do the stars appear like point

objects?

4. What is a constellation? How does the

constellation differ from a star?

5. what is the name a star which appears stationary from the earth. In which constellation is it situated?

6. What is "a light minute?" How many light minutes is the earth from the sun? Express this distance in kilometers?

7. How much time is involved from one new moon to another new moon as seen from the surface of the earth?

8. In how much time does the moon

complete one rotation about its own axis?

15.7 Planets

A solid heavenly body which

revolves around the sun in a well defined

orbit is called planet.

If you carefully look at the clear night

sky, you will find some objects which (i)

appear bigger and brighter than the stars (ii) they do not twinkle (iii) they change their position with respect to the other stars.

These bright objects are planets, which

means wanderers, as they change their

position in the night sky.

There are nine planets in all,

including the earth. They have no light of

their own, but appear to shine as the

sunlight from their surface is reflected. All

planets (except Venus) rotate from the west

to the east. Due to different speeds of planets the position of them with respect to the earth changes every day. these planets are called Graha In Indian

astronomy, all planets revolves around the sun.

The list of all the planets in the order

of increasing distance from the sun is given below, along with their Hindi names

Name of Planet.             Name of Planet

(in English).                          (in Hindi)

1. Mercury                                 Budha

2. Venus                                      Shukra

3. Earth                                      Prithvi

4. Mars.                                      Mangal

5. Jupiter                                    Brihaspati

6. Saturn                                    Shani

7. Uranus.                                   Indra or Arun

8.Neptune                                  Varun

9. Pluto                                       Yama

15.8 The Solar System

Sun is the nearest star for us on the earth. It is believed that the sun was born 5 billion years (500 crore years) ago. It has been emitting a huge amount of heat and light and is expected to do the same for another 5 billion years. The sun along with the nine planets and their moons constitutes the solar system moreover In addition to the planets and their moons, other heavenly bodies have been found to revolve around the sun. They are asteroids, comets and meteors. Let us study more about them.

Asteroids

The small piece of rocks or metal which revolve around the sun, in between the orbits of the mars and jupiter asteroids (meaning star like or minor planets).

Asteroids are not visible to the

unaided eye, but can be easily seen

through a powerful telescope. They are of

different sizes, the largest being Ceres,

which is 633 km in diameter. It is estimated that there are around 100,000 asteroids. Each asteroid has its own orbit. Actually the orbits of asteroids are spread over a large distance forming a band.

There are two schools of thought in

formation of asteroids.

1. According to one school, these are

original rocks and the metal chunks,

which failed to form a planet, when other

planets were formed in the solar

system.

2. According to the second school of

thought, they are the debris of a planet

which collided with a moon of the

Jupiter.

Following were the decisions of the General

Assembly of IAU on 23rd August 2006.

1. A planet is a body in near circular orbit

around a star (in our case sun), which is

big enough for the force of gravity to

make it round and should not take more

than 2 centuries to revolve around the

Sun.

2. planet Pluto takes 248 years to revolve around

the Sun, so it is disqualified as a planet.

3. Now Scientifically the Pluto and objects beyond it are called 'plutons', new members of solar family. The order of plutons is (1) pluto (ii) charon, (iii) 2003 UB,19-From August 2006 onward:

(i) There are eight planets revolving around the Sun.

(ii) There are three plutons revolving

around the Sun, beyond neptune, in

highly tilted orbits.

(iii) Mercury is the nearest planet from the

Sun.

(iv) Neptune is the farthest planet from the Sun.

(v) Pluto is the first member of plutons.

(vi) Next to pluto is charon and finally 2003

UB-

(vii) Plutons have highly tilted orbit and take

more than 200 years to revolve around

the Sun.

TEST YOURSELF

1. What is a planet? How many planets

revolve around the Sun?

2. Name the planet which (I) is nearest to the

sun (ii) is farthest from the Sun (ii)

supports life?

3. Name the planet which (i) revolves

around the sun from east to west (ii)

intersects the orbit of another planet?

4. Name one planet that was predicted

before its discovery?

5. Name the planet having (i) largest

number of moons (II) a system of number

of rings?

6. What is the solar system? Name all the

planets of solar system in the increasing

order of distance from the sun ?

Exercises

1. Fill in the blanks by choosing correct words from the following list:

List: meteorite, pluto, moon, planets, universe, core, comet, constellation.

(1) The branch of science which deals with the study of

is called astronomy.

(ii) The unburnt part of a meteor which reaches the earth is called

(iii) The heavenly bodies which revolve around the sun are called_

(iv) The heavenly bodies which revolve around the planets are called

(v) The orbit of

is not in the same plane as that of the other planets.

(vi) A heavenly body with along tail, moving around the sun in an elliptical path is called

(vii) In the

of the sun, hydrogen gas fuses with the liberation of the energy.

(viii) A group of stars which resembles an animal or some other known object is called

2. Statements given below are incorrect. Write correct statements.

(i) Halley's comet visits our solar system after 26 years.

(ii) Helium gas constitutes most of the atmosphere of the sun and the stars.

(iii) Pole star is nearest to our solar system.

(lv) Astronomers have divided the sky into 68 constellations.

(v) Meteors on burning leave behind gold dust and light.

(vi) The orbit of neptune is different from the orbits of the other planets in the solar system.

(vii) Mars is the second planet nearest to the sun.

(viii) Moon revolves around the earth in 21½ days.

3. Answer the following questions:

(i) What is universe ? Name six different kinds of heavenly bodies found in the universe ?

(ii) With the reference to the average distance from the sun, state: (a) the serial number of the

planet earth (b) the average distance of the earth from the sun (c) the time in which the sunlight

reaches the earth?

(iii) (a) Name the natural satellite of the earth?

(b) In how many days does this satellite complete one revolution around the earth?

(c) In how many days does this satellite rotate around its own axis?

(d) How does the gravity of this satellite compare with the earth?

(e) State the maximum temperature on the day side and minimum temperature on the

night side of this satellite?

(iv) What do you understand by the following terms (a) New Moon (b) Full Moon?

(v) (a) Define solar system?

(b) Name all the planets in the solar system in the order of their distance from the sun ?

(vi) (a) How many moons mars have?

(b) Write the name of these moons?

(vii) What is comet? Why does a comet develop a tail while approaching the sun?

(viii) What is star? What makes the star give about vast amount of energy?

(ix) (a) How are meteors different from stars?

(b) How are meteors different from meteorites?