stars, class 8

Celestial object:  the object present outside the earth in the space is called Celestial object 

for example other planet ,asteroids etc.

Astronomy : it is the branch of science who is deal with the celestial objects and their phenomena.

Moon

• Moon is the nearest celestial object of Earth
• it is seen as bright as object during night 
• it is Earth's neutral satellite
• Does not have its own light it reflects the light of sun.
• At night we see different shapes of moon this is known as phases of moon 
• Moon also revolve on its own axis in 29.5 (29 days 12 hour 44 minutes 3 seconds) days called synodic month.
• Moon absorbed delight of sun and reflect it in night due to which it affairs bright at night that is eliminated at night
• Moon complete one revolution on its axis and  in same time it also complete one revolution around the earth that's why the half part of the moon always get the sunlight while other half does not receive any sunlight this side is known as dark side of moon
• India send mission chandrayaan -2 in this dark side 
• the moon have dusty and barren surface with crackers steep and high mountains 
• on 21 July  1969 need almond strong landed on the moon for the first time followed by Edwin eldren 
• the gravity of moon is 1/6 of earth.
• The size of moon is one fourth (1/4) the size of Earth 
• moon is also known as Fossil planet
• the maximum distance of moon from earth called apogee. and the minimum distance is called Perigee 

Phases of moon:

there are eight phases of moon. in order they are new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter and waning crescent.

This cycle repeats once a month (every 29.5 days)

position 1: the back part of moon does not get the sunlight due to which the moon do not illuminate at night this face is known as new moon

position 2:  in this position 1/4th part of moon is visible called waxing crescent moon 

position 3 : in position 3 the half moon is visible is called first half moon

position 4 in this position 3/4th of the moon is visible and called waxing gibbous moon 

position 5:  at this position full moon is visible as a circular disc called full moon

position 6:  at this position again 3/4th of moon visible called waning gibbous moon 

position 7 at this position half of the moon is visible called last quarter moon 

position 8 at this position again 1/4th of the part is moon visible called waning crescent moon

Star :

• it is a celestial object which has its own light .for example Sun is also a star and it is the nearest stars of our solar system and other stars are far from the earth so they appear very small and very little light reach to earth . 
• the sun near to the earth so we get more light from the sun that's why other stars do not appear in the day while they can be seen at night. 
• the stars appear twinkling at the night due to the phenomena atmospheric refraction.
•  the first and the brightest star seen in the evening is called pole star. It does not change its position with time it always pointed north direction.
• it helps in nevigation for the passengers at night in olden days .

alpha sanctuary it is the nearest star of our solar system it is about 4.3 light year away from the earth 

light year it is a distance travelled by light in one year . it is an astronomical unit and used to measure the distance between the celestial objects like distance between star

one light year:  the distance travelled by light in one year.

1 light year: speed of light × time taken( second)

=  3 × 10^ 8 m/sec ×( 365 ×24× 60× 60)

= 9.46 × 10 ^ 15 m 

= 9.46 × 10^12 km

• the time taken by sunlight to reach the earth from the sun is 8 minute 16 second

constellations : it is a group of stars that form and the recognisable shape in the night .

• they are the device by which ancient peoples navigate at night 
• there are 88 constellation recognized by international astronomical union(IAU)

some example of constellations:

Ursa major:

• it is also known as saptarishi, great bear or big dipper.
• there are seven prominent stars in this constellation the , three stars make the handle of the dipper while the other four make the dipper (bowl).
•  if we join the first two star of the dipper then it always points towards the pole star.

• the direction the pole star is only seen in northern hemisphere, it cannot be seen through southern hemisphere 

saptrishi: 

• Atri
• Bharadvaja
• Gautama Maharishi
• Jamadagni
• Kashyapa
• Vasistha
• Vishvamitra

Orion:

• Orion is most visible in the evening sky from January to April,
• Orion is another well-known constellation that can be seen during winter in the late evenings.
• It also has seven or eight bright stars
• Orion is also called the Hunter. The three middle stars represent the belt of the hunter. The four bright stars appear to be arranged in the form of a quadrilateral.
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• The star Sirius, which is the brightest star in the sky, is located close to Orion.
• To locate Sirius, imagine a straight line passing through the three middle stars of Orion
• line towards the east lead you to a very bright star. It is Sirius
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Cassiopeia

• Cassiopeia is another prominent constellation in the northern sky. 
• It is visible during winter in the early part of the night. It looks like a distorted letter W or M

The Solar System:

The Sun and the celestial bodies which revolve around it form the solar system.

It consists of large number of bodies such as planets, comets, asteroids and meteors.

Planets:

• Planets are the opaque bodies which continuously evolve around and are lightened by sun.
• they does not have their own light
• there are eight planets in our solar system 
• the sequence of planet according to their distance from the sun is Mercury, Venus ,Earth ,Mars ,Jupiter Saturn, Uranus .
• Jupiter is the biggest and the Mercury is the smallest planet of the solar system 
• the time taken to complete one revolution in one orbit is called period of revolution
• the planet's revolve around the sun in a fixed path called orbits
• the orbits are elliptical in shape 
• the eight planet are divided into two groups i.e terrestrial  planets (rocky planets) and Jovian planets (gaseous planet).
•  the four planets near the sun i.e. Mercury, Venus, Earth and Mars are called terrestrial planet because  their structures is similar to the earth and made of stone and soil.
• the other four planets Jupiter ,Saturn, Uranus and Neptune are called gaseous planets are planets in our planets the include Mercury Venus Earth Mars
• the two group are separated by asteroid belt.

Inner planet	Outer planet.
Mercury, Venus, Earth and Mars	Jupiter ,Saturn, Uranus and Neptune
they are near to sun	they are far from the Sun
they are made up of dense minerals	they are made up of hot gases mainly hydrogen and helium
they move faster and have a shorter period of revolution	the move slowly and have a longer period of revolution
they have thin rocky crust	they are all gases bodies
they have a mantle rich in iron and magnesium	they are made of gas
they have a core of molten metals	they have ring system around them
They  have thin atmosphere
they have very few satellites or no satellites,	they have a large number of natural satellites that is moon

some planets 

Mercury (Budh)

• Mercury is the closest planet to the sun 
• it is extremely hot this planet has no water on it 
• Mercury have no gas likes CO2, H2 O2 which  act as building block of life 
• Mercury have no protective blanket like ozone 
• it is usually hidden due to sun glare 

Venus (Shukra)

• Venus is the second planet in the distance from the Sun 
• this planet is nearest to the earth and is also the brightest planet 
• Venus is also known as evening start as well as morning star 
• Venus is surrounded by a thick cloud  known as Veiled planet 
• Venus is like the Earth in size and Mars and hence also known as Earth's twin.
• it also rotates clockwise like  Uranus
• Venus is the hottest planet even hotter than Mercury of our solar system due to its veil  cloud
• Venus has no water there is no sufficient oxygen

Earth (Prithvi)

• Earth is the largest of the inner planet 
• the earth is 23(1/2)  degrees tilted on its axis 
•  it take 23 hours 56 minutes and 4 seconds to rotate on its axis
•  it take 365 days 5 hours and 48 minutes to revolve around the sun 
• it is also known as watery planet or blue planet due to presence of amount of water on it
• Earth is only planet that  sustain all life on it 
• it has large quantity of oxygen which support life 
• Earth also have carbon dioxide, nitrogen ,oxygen which act as building block of life
• the earth is neither too hot not too cold it has Goldilock zone
• Goldilocks zone make it suitable for life 
• Earth has a protective blanket of ozone layer

Mars:(Mangal)

• it is also known as red planet due to presence of ferrous oxide on its surface 
• it has two natural satellites : phobos and diamos.

Jupiter (Brihaspati)

• It is the largest planet of the solar system. it is also known as winter planet because the temperature is very low minus 148°
• Gannymeda is largest satellite
•  it has 67 moons
•  it can accommodate 1300 Earth 
• Jupiter has a red spot which is a strom and surviving for many years and it is twice wide as Earth

Saturn (Shani)

• It is the second largest planet of solar system 
• it has unique beautiful rings around 
• it made up of ice and dust
•  it has 82 natural satellites 
• Titan is largest satellite.
• Saturn is less dense than water

Uranus 

• it is 4th time bigger in size than Earth 
• it rotate from east to west direction which is opposite to other planets accept Venus.
•  it is used tilted from its access so call up planet on its side
•  it is the third biggest planet it also have 13 rings  

Neptune

• it is 8th planet of solar system 
• it is similar to Uranus and considered as twins.
• it is surrounded by methane gas 
• it is it has strong winds which is more powerful than other planets

Pluto 

• Pluto was given a new name as dwarf planet in September 2006
• it loses it to planatery status on 24 August 2006.

comets:

• these are the celestial bodies that revolve around the sun in an elliptical orbit 
• they are also called as visitor of solar system
• comets are made up of frozen gas which are hold together Rocky and metallic materials
• comet become visible only when it travel close to the sun 
• it's ice melt and the gas and the dust is sweep back into a tail
• they have very long tail that always directed away from the sun
• when the commit travel close to the sun the ice melt to a head of gas called a Coma 
• Halley’s comet, which appears after nearly every 76 years. It was last seen in 1986 next seen in 2061.

meteors and meteorites:

• Meteor originate from the asteroid belt ,when two meteor suddenly collide and broken into pieces some of the their parts are moved towards the Earth  and due to gravity of earth the attract toward the surface of Earth.
• due to friction between atmosphere they burn and evaporate before it reaching to the surface,it is seen as streak bright light in the sky.these are called meteors.
• when the material is large and start to the surface of Earth called meteorites.
• Meteorites help scientists in investigating the nature of the material from which the solar system was formed

Meteor Showers : When the Earth crosses the tail of a comet, swarms of meteors are seen.

These are known as meteor showers.

artificial satellite:

• they are men made objects that are launched from earth and evolve around the earth much closer than the natural satellite.
• Aryabhatta was the first Indian satellite. Some other Indian satellites are INSAT, IRS, Kalpana-1, EDUSAT, etc.
•  it is are of two type: polar satellite and geostationary satellite

Polar satellite	Geostationary satellite
they revolve around the polls	they revolve around the equator
they revolve closer to the earth than Geostationary satellites	they revolve away to the earth than polar satellites
there is speed is high so that their revolve the earth three to four times in a day	they have comparatively slow speed than polar satellite they take 24 hours to revolve around the Earth thus looks stationary from the Earth's surface
they are used for weather forecasting ,ore search etc.	they are used for telecommunication,remote sensing etc