Astronomy

d.b.gaekwad
TGT/S.SC. , JNV PARBHANI

aSTRONOMY - MeaNINg
The word Astronomy is derived from the greek
word , “Astron” meaning , “ Star” and “Nomy”, is
derived from the word , “ Nomos” means , “ Law or
Culture” .
Astronomy is a , “Law or Culture of Stars”.
Astronomy is a natural science , that is the study
of Celestial objects- planets, stars, moons ,
nabulae and galaxies. The physics, chemistry,
mathematics of evolutions of such objects out side
the earth’s atmoshphere

eaRLY aSTRONOMeRS
 Astronomer - Astronomers use the principles of
physics and mathematics to learn about the
fundamental nature of the universe, including the
sun, moon, planets, stars, ...
 Nicholas Copernicus – (1473 – 1543) the first
astronomer to teach that the sun (not the Earth)
was the center of the solar system.
 Galileo Galilei – built the first telescope in
1609 and proved Copernicus correct.

whaT IS OuT TheRe?
• Ever since mankind has looked up at the
moon and stars, we have wandered about
life in the universe.

whaT IS a uNIVeRSe ?
• The Universe is commonly defined as the
totality of
existence, including planets, stars, galaxies,
the contents of intergalactic space, and all
matter and energy.
• The universe was born with the Big Bang as
an unimaginably hot, dense point. When the
universe was just 10-34 of a second or so old

hOw bIg IS The uNIVeRSe?
• Billions of stars – planets – galaxies

The uNIVeRSe
• A small portion can be observed only of the
entire universe.
• Because the universe is only about 14 billion
years old, light has only had about 14 billion
years to travel through it. Therefore, the most
distant regions of the universe we can see are
about 14 billion light-years away.
• This is the extent of the "observable
universe," but the entire universe is probably
much larger. It could even extend infinitely in
all directions.

LIghT YeaR
A light year is a unit of
distance
It is the distance that light
can travel in one sidereal
year
Light moves at a velocity
of about 300,000 kilometers
each second
So 300,000 km/sec x 60
sec/min x 60 min/hr x 24
hr/day x 365 days/year or:
In one year light can travel
about 9.46 trillion kilometers

LIghT YeaR
• More specifically, a light year is
defined as the distance a
photon would travel, in free
space and infinitely far from
any gravitational or magnetic
field in one Julian year (365.25
days of 86400 seconds each)
• Light is used to measure
distance since it is the fastest
thing in the Universe

whaT IS a LIghT YeaR
• A light year is a unit of
distance, NOT a unit of time
• A light minute and a light
second are units related to
the light year
• A light minute is equal to
17,987,547 kilometers
• A light second is equal to
299,793 kilometers
• The Moon is 1.2 light
seconds away from Earth

whaT IS LIghT YeaR

The Solar System

Our entire Solar System
out to Pluto is only one
eight-hundredth of a light
year across
The distance to our
nearest neighbors, Alpha
Centauri and Proxima
Centauri, is 4.3 light years

whaT IS a LIghT YeaR
• Our Milky Way Galaxy is
100,000 light years
across
Milky Way Galaxy • The distance to our
nearest galaxy, the
Andromeda Galaxy, is
2,300,000 light years
• Recently the Universe has
been calculated to be at
least 156 billion light
years across

LIghT YeaR: gOINg baCk IN TIMe
Because a light year is directly
related to the time light takes to
travel through space, it follows
that as we look out into the
universe we also look back in
time
If a star is 1 million light years
away, it has taken 1 million
years for the light to reach us,
and the light we are seeing was
created 1 million years ago
So we are seeing the star as it
looked 1 million years ago, not
how it looks today

whaT IS LIghT YeaR

The Crab Nebula

In about 5,350 BC a star in the constellation
Taurus exploded
That star was about 6,300 light years away
from Earth meaning that the light from the
explosion took 6,300 years to cross the
intervening space
That light finally reached Earth in 1054 AD
—that was the date Earthbound observers
saw the explosion that created the Crab
Nebula
Therefore when we look at the Crab Nebula
today we see it as it as it was in about
4,300 BC

aSTRONOMICaL uNIT
 The distance from Earth to the
Sun is one Astronomical Unit.
 The A.U. helps make the vast
distances in our Solar System
more manageable
 Anything closer than Earth is a
fraction of an A.U.
 Anything further away is a
multiple of an A.U.

TheORIeS ON ORIgIN OF OuR eaRTh
 GEORGES DE BUFFON’S THEORY OF
COMET’S COLLISION.
 EMANUEL KANT’S THEORY OF
GASEOUS MATTER.
 INTER STELLER DUST HYPOTHESIS
OF OTTO SCHMIDST.
 BINARY STAR HYPOTHESIS OF
RUSSEL & LITTLETON

geORgeS de buFFON’S TheORY
 A Comet about to collide with
the Sun.
 The Collision results in
release of material from the
Sun.
 Released material condenses
and acquires the shape of
planets which starts revolving
around the Sun.

LIMITaTIONS TO The TheORY
 Buffon’s theory fails to explain the
peculiar position of planets around the
sun which are arranged in such a manner
that the largest ones occupy the middle
orbits while the smaller ones occupy the
marginal orbits.

eMaNueL kaNT’S TheORY OF gaSeOuS MaTTeR
 Cold fragments of the primordial
matter attracted towards each other
by gravitational pull.
 High temperature and angular
velocity transform the matter into a
gaseous state.
 Centrifugal force throws out
concentric rings of the gaseous
matter.
 Concentric rings condense and
acquire the shape of Planets and
Sub Planets.

LIMITaTIONS TO The TheORY
 Failed to explain the sudden coming
into play of the gravitational pull and
the source of angular motion for the
particles.

INTeR STeLLeR duST
hYPOTheSIS OF OTTO SChMIdST
 Dust particles revolving around
the Sun under the influence of
the gravitational pull.
 The dust particles starts
consolidating by colliding with
one another.
 Eventually nine planets and
their sub planets emerge.

LIMITATIONS TO THE THEORY
 Schmidst failed to explain the primordial
existence of dust, clouds and their
attraction towards the Sun considering
the great distances between Stars in the
Universe

BINARY STAR HYPOTHESIS OF
RUSSEL & LITTLETON
 The Sun existed in “Binary
Companionship” with a “Companion
Star”.
 A third star happened to pass by this
Binary arrangement.
 Pull being exerted upon the
companions star by the sun and the
third star resulting in separation of
materials from the companion star.
 Fragments of the companion star
getting transformed into planets which
revolves around the Sun.

LIMITATIONS TO THE THEORY
 This hypothesis does not explain the
placement of the Planets in different
orbits at varying distances from the
Sun.

GALAXY
 The word galaxy is derived from the Greek
word “ Galaxias” literally “Milky",
 Galaxies range from dwarfs with as few as ten
million (107) stars to giants with one
hundred trillion (1014) stars,each orbiting their
galaxy's own center of mass.
 Galaxies contain varying numbers of star
systems, star clusters and types of interstellar
clouds. In between these objects is a sparse
interstellar medium of gas, dust, and cosmic
rays. Super massive black holes reside at the
center of most galaxies. They are thought to
be the primary driver of active galactic
nuclei found at the core of some galaxies. The
Milky Way galaxy is known to harbor at least
one such object.

THE NAME OF OUR GALAXYAAKASH GANGA MILKY WAY
• The name of our galaxy is the Milky Way. Our Sun and
all of the stars that you see at night belong to the Milky
Way. When you go outside on a dark night and look up,
you will see a milky, misty-looking band stretching
across the sky. When you look at this band, you are
looking into the densest parts of the Milky Way, the
"disk" and the "bulge."

WHERE IS THE SUN LOCATED
 The Sun is near the inner rim of

The Sun's location in
the Milky Way Galaxy.
The angles represent
longitudes in
the galactic coordinate
system.

the Galaxy's Orion Arm.
 The Sun is currently 16–98 Light
year from the central plane of the
Galactic disk.
 It takes the Solar System about
240 million years to complete one
orbit of the Galaxy (a Galactic
year),so the Sun is thought to have
completed 18–20 orbits during its
lifetime and 1/1250 of a revolution
since the origin of humans.

WHAT IS A GALACTIC YEAR
 The galactic year, also known as a cosmic year, is the
duration of time required for the Solar
System to orbit once around the center of the Milky
Way Galaxy.
 Estimates of the length of one orbit range from 225 to
250 million "terrestrial" years.
 According to NASA, the Solar System is traveling at
an average speed of 828,000 km/h (230 km/s) or
514,000 mph (143 mi/s) relative to the galactic
center,which is about one 1300th of the speed of light.
If you could travel at that speed in a jet aircraft along
the equator, you would go all the way around the world
in approximately 2 minutes and 54 seconds.

WHERE ARE YOU IN THE UNIVERSE
• 25,000 light years from the galaxy
center, in the Orion Arm, which is
roughly halfway between the
center and the edge.
• its at the edge near one of the
spiral ends......
• we’re located in a minor arm of
the galaxy. Our local spiral arm is
sometimes Orion Arm, or
sometimes the Orion Spur. It’s
between the Sagittarius and
Perseus Arms of the Milky Way.

SOLAR SYSTEM
• A solar system is the collection
of planets, asteroids, and moons
(moons orbit the planets) that
occupy a space around a sun
and are held within the
gravitational pull of the Sun. Our
solar system consists of eight
planets (Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus,
Neptune) and a planetoid, Pluto.

PLANETS- DEFINITIONS
 The word planet is derived from the Greek word,

“Planetai” which means a “Wandering Star”.
 On september 13,2006 International Astronomical Union
adopted the following definition of a Planet:A. A "planet“ is a celestial body that is in
orbit around the Sun .
B. Has sufficient mass for its self-gravity to overcome
rigid body forces so that it assumes a hydrostatic
equilibrium (nearly round) shape.
C.Has cleared the neighborhood around its
orbit. i.e. doesn’t allow any other celestial
object to intersect its orbit

OUR PLANETS
In the order of their proximity to the sun









My – Mercury
Very – Venus
Elegant – Earth
Mother – Mars
Just – Jupiter
Served – Saturn
Us – Uranus
Nuts – Neptune

THE SUN
• The Sun is the star at the center of
the Solar System
• The Sun is composed primarily of
the chemical
elements hydrogen and helium; they
account for 74.9% and 23.8% of the
mass of the Sun in the photosphere.
• It has a diameter of about
1,392,684 km around 109 times that
of Earth, and its mass is approximately
330,000 times the mass of Earth.

THE SUN
•
•

•

The surface of the sun is called the
photosphere.
The photosphere is 340 miles thick and it's
temperature s range from 5,500 °C to
6,000 °C. It has dark spots called sunspots
which are the only solar activity observable
by the naked eye.
The source of the sun's fuel is hydrogen
and helium gases. Through a special
chemical reaction, called nuclear fusion,
the hydrogen gas is "burned" releasing an
enormous amount of energy in the form of
light and heat.

MERCURY
 Distance (From Sun) :- 58
Million Kms.
 Revolution Motion :-88
Days.
 Rotation Motion :- 59 Days.

VENUS
• Distance (From Sun) :- 108
Million Kms.
• Revolution Motion :- 255 Days
• Rotation Motion :- 243 Days
• It is also known as Morning
Evening Star
• It could be seen hour befoe
Sun rise and after Sun st.
• Twin sister of the Earth
• Known as Red Planet

VENUS TRANSIT

Image of the 2012 Transit taken by
NASA's Solar Dynamics Observatory
spacecraft

VENUS TRANSIT
• A transit of Venus across
the Sun takes place when
the planet Venus passes directly
between the Sun and Earth (or
another planet), becoming visible
against (and hence obscuring a
small portion of) the solar disk.
• During a transit, Venus can be seen
from Earth as a small black disk
moving across the face of the Sun.
The duration of such transits is
usually measured in hours (the
transit of 2012 lasted 6 hours and 40
minutes)

DIFFERNCE BETWEEN TRANSIT
& ECLIPSE

• Transit is the
passage of a
planet across
the disk of the
Sun - only
transits of the
inner planets
Mercury and
Venus are
possible
• A transit

• An eclipse in
when the moon
passes in front
of the Sun.

• An eclipse
totally hides
what it is in
front of.

EARTH
• Distance ( From the
Sun) :- 150 Million Kms.
• Revolution Motion :365 Days 5 Hours 48
Minutes 43 Seconds
• Rotation Motion :-1 Day
(24 Hours )
• Known as Blue Planet
• Life is found .

eaRth -the Blue Planet
• Equatorial
Circumference :12756 Kms.
• Polar Circumference
:- 12714 Kms.

the Moon - the onlY
Satellite of the eaRth

the Moon - the onlY Satellite
of the eaRth
 Perigee Distance :- 3 Lakh 84 Thousand
Kilometers.
 Apogee Distance :- 4 Lakh 6 Thousand Kilometers.
 Circumfernce is - 3476 Kilometers .
 Highest mountain is Libnitus located at south
pole.
 Highest peak is 35000 ft.
 Ratio of Gravity between moon to earth is 0.166
 Revolution time of the moon around the earth is 27
Days 7 Hours 43 Minutes 11. 47 Seconds

RelationShiP BetWeen Moon
& the eaRth
A. Tides occurs due to
the gravity pull of
the moon
B. Tides
C. Lunar Eclipse occurs
when sun earth and
the moon comes in a
straight line.
D. Solar Eclipse occurs
when sun the moon
and the earth comes

MiSSion ChanDRaYan
 THE WORD CHANDRAYAAN – 1 IS DERIVED FROM A
SANSKRIT WORD LITEARLLY MEANING MOON
VECHILE.
 IT IS INDIA’S FIRST MISSION TO MOON DEVOLPED
BY ISRO (INDIAN SPACE RESARCH ORGANISATION).
 THE MISSION INCLUDES A LUNAR ORBITER AND AN
IMPACTOR.
 IT WAS LAUNCHED ON 22 OCTOBER 2008 WITH
HELP OF A MODIFIED VERSION OF PSLV XL FROM
SATISH DHAWAN SPACE CENTRE, SRIHARIKOTA,
ANDHRA PRADESH AT 6:23 IST.
 ESTIMATED COST - RS 386 CRORE
(US$ 80 MILLION)

MiSSion ChanDRaYan
 THE IDEA OF UNDERTAKING AN INDIAN
SCIENTIFIC MISSION TO MOON WAS INITIALLY
MOOTED IN A MEETING OF THE INDIAN
ACADEMY OF SCIENCES IN 1999 THAT WAS
FOLLOWED UP BY DISCUSSIONS IN THE
ASTRONAUTICAL SOCIETY OF INDIA IN 2000.
 A NATIONAL LUNAR MISSION TASK FORCE WAS
CONSTITUTED BY THE INDIAN SPACE
RESEARCH ORGANISATION (ISRO) PROVIDED
AN ASSESSMENT ON THE FEASIBILITY OF AN
INDIAN MISSION TO THE MOON AS WELL AS
DWELT ON THE FOCUS OF SUCH A MISSION
AND ITS POSSIBLE CONFIGURATION.

SPeCifiCation of ChanDRaYan


MASS:-

1380 KG AT LAUNCH, 675 KG AT LUNAR
ORBIT, AND 523 KG AFTER RELEASING THE
IMPACTOR.
 DIMENSIONS:
CUBOID IN SHAPE OF APPROXIMATELY 1.5M.
 POWER:MAINLY POWERED BY ITS SOLAR ARRAY,
WHICH INCLUDES ONE SOLAR PANEL
COVERING A TOTAL AREA OF 2.15 X 1.8 M
GENERATING 700 W OF POWER, STORED IN A
36 A-H LITHIUM-ION BATTERY.USES A
BIPROPELLANT INTEGRATED PROPULSION
SYSTEM.

SPeCifiCation of
ChanDRaYan







IT HAS THREE SOLID STATE RECORDERS (SSRS)
ONBOARD TO RECORD DATA FROM VARIOUS
PAYLOADS.
SSR-1 WILL STORE SCIENCE PAYLOAD DATA AND
HAS CAPABILITY OF STORING 32GB DATA.
SSR-2 WILL STORE SCIENCE PAYLOAD DATA
ALONG WITH SPACECRAFT ATTITUDE
INFORMATION (GYRO AND STAR SENSOR),
SATELLITE HOUSE KEEPING AND OTHER
AUXILIARY DATA. THE STORING CAPACITY OF
SSR-2 IS 8GB.
M3 (MOON MINERALOGY MAPPER) PAYLOAD HAS
AN INDEPENDENT SSR WITH 10GB CAPACITY.

PaYloaDS of ChanDRaYan
• THE SCIENTIFIC PAYLOAD
HAS A TOTAL MASS OF 90
KG AND CONTAINS FIVE
INDIAN AND SIX FOREIGN
INSTRUMENTS .

1
2

3

 INDIAN PAYLOADS
1.TERRAIN MAPPING
CAMERA
2. HYPER SPECTRAL
IMAGER
3.LUNAR LASER RANGING
INSTRUMENT
4.HIGH ENERGY X-RAY
PAYLOAD
5. MOON IMPACT PROBE

FIRST PICTURE SENT
BY CHANDRAYAN

inDia’S SatelliteS SinCe
inDePenDenCe
•
•

Aryabhata was India's first satellite.
It was launched by the Soviet Union
on 19 April 1975 from Kapustin
Yar using a Kosmos-3M launch
vehicle.
• It was built to conduct experiments
in X-ray astronomy, aeronomics, and
solar physics. The spacecraft was a
26-sided polygon 1.4 m in diameter.
• The satellite reentered the Earth's
atmosphere on 11 February 1992.
It was 360kgs.

aRtifiCial Satellite-hoW
Sent

Shroud

Protects the spacecraft

Upper stage
Orbit insertion rocket
engines and
propellant tanks

Main vehicle
Primary liquid or solid
rocket propellant
tanks

Booster packs

Solid strap-ons for some
rockets to increase initial
thrust

Engine /
nozzles

Mechanism for combining
propellants and focusing

Step 7: Mechanical deployments

Step 6: Satellite initial checkout
Step 5: Orbit insertion
Step 4: Shroud opening
Step 3: Main engine cut-off and
separation

Step 2: Booster cut-off and separation

Step 1: Ignition and launch

launCh SeQuenCe
Step 1

AV
North
NORTH
POLE
Pole

AV

Step 2
Step 3

Launch into parking orbit
(With orbit insertion burn)
Minimum energy transfer
Burn 1 to change path
Burn 2 to change to higher
orbit
AV

Orbit plane transfer
(With vector thrust burn)

launCh funDaMentalS
force = (mass) x (acceleration)
f = (m)(a)
The thrust of a launch vehicle must
oppose gravity and atmospheric
drag
To get into orbit, a vehicle must achieve a velocity
FORCE TIME
FORCE & TIME &
of FORCE 24 (24 times&the speed of sound)FUEL
mach

Thrust = Pounds or Kg

Impulse = Pounds per sec
= Newtons per sec

Specific Impulse (Isp)
Isp =
Thrust (lb)
fuel weight (lb) burned in

aRounD in oRBit
V
V

NORTH
POLE

LAUNCH INTO PARKING ORBIT
(WITH ORBIT INSERTION BURN )

ORBIT PLANE TRANSFER
(WITH VECTOR THRUST BURN )

V2

NORTH
POLE

V1
HOHMANN (MINIMUM ENERGY)
TRANSFER
(BURN 1 TO CHANGE TO ELLIPTICAL
ORBIT AND BURN 2 TO CHANGE TO

NORTH
POLE

V2

V1
FAST TRANSFER
(BURN 1 TO CHANGE TO LARGE ELLIPSE AND
BURN 2 TO FORCE INTO NEW ORBIT)

STAGE OF LAUNCH VEHICLE
• The technique, called staging,
is used in all current launch
vehicles.
• There are two standard forms
of staging: serial staging and
parallel staging.
• In serial staging the stages are
stacked vertically in the rocket
and are fired one after another.
• Parallel staging uses stages
strapped alongside each other
which are fired
simultaneously.
• Most launch vehicle use both

LAUNCH TO GEOSTATIONAry
OrbIT

• It is normal for launch vehicles
to have 3 stages, and for each
stage to be dropped as its
propellant is consumed.
• The first stage uses a single
powerful engine, the Vulcain.
• Heavy lift rockets like the
Ariane 5 have two or more
solid rocket boosters (SRB) to
help the launcher to lift
heavier satellites
• Both the main engine and SRB
are ignited at lift off
• The SRB are jettisoned about 2
minutes into the flight when
their fuel is spent 

OrbIT

• About 8 minutes into the
flight the first stage has
consumed all its fuel.
• The first stage is
jettisoned and the second
stage engine ignites 
• The payload is protected
by an aerodynamic fairing
inside the atmosphere.
This is not needed when
the rocket is in space so it
is jettisoned 

OrbIT
• About 25 minutes into the flight
the seond stage has consumed
all its fuel and is jetissoned 
• The third stage is ignited. and
burns until the correct velocity
has been achieved. At this
time it is shut down 
• The satellite has enough speed
to coast to 36000 km altitude,
the highest point of the flight.
• This highest point is called the
apogee

OrbIT

• The launch vehicle needs
to accelerate the satellite
to a horizontal velocity of
10.3 km/s at an altitude of
about 500km.
• This puts the satellite in an
elliptical geostationary
transfer orbit (GTO)
• In this orbit the satellite
will coast up to the
geostationary orbit at
36,000 km altitude
• Gravity slows the satellite
until, at 36000 km, it is only
travelling at 1.6 km/s

OrbIT
• The satellite completes
several orbits of the GTO
while its electronic systems
are powered up.
• AT the highest point, called
apogee, the satellite fires
its own rocket motor, called
the apogee boost motor
ABM)
• The ABM accelerates the
satellite from 1.6 km/s to 3.1
km/s, putting the satellite
into a circular orbit at 36000
km altitude. It is now in the
geostationary orbit.

MArS
• Distance from the Sun
:- 228 Millions kms.
• Its Atmosphere is very
thin.
• It has two Satellites:Diamos & Phobos.
• Rotational Motion :24.64 Days.
• Revolution Motion :687 Days.

ASTErOID
• Fragmented Mass of
the Dead Planets
lying between Mars
and Jupiter is called
Asteroids.
• These also revolves
around the Sun like a
Planets.
• But they do not have
any atmosphere or
life.

JUPITEr
• Distance :- 778 Millions
Kms.
• Atmosphere is basically
made up of Hydrogen and
Helium .
• The outer surface is made
up of methane and
Ammonium
• Total number of
Satellites :- 28
• Faint Ring surrounds the
Jupiter
• So big that 1300 Earth
sized planets could be

FOUr bIG SATELLITES OF
JUPITEr
•
•
•
•

Io
Europa.
Ganymede
Calisto

SATUrN
• This Planet is located
two times farthest the
Distance between
Jupiter and the Sun i.e.
1,427 Million Kms.
• With the help of
Binoculars one could see
the Three Distinct Rings
of Saturn.
• Revolution Motion :29Years 5 Months
• Rotation Motion :- 10 Hrs
40 Minutes

FIVE SATELLITES OF SATURN

TITAN

MIMAS

DIONE

TETHYS

RHEA

UrANUS (ArUN)
• Harshel discovered this
Planet in 1781 A.D.
• Atmosphere is primarily
composed of Hydrogen and
Helium.
• Distance from the sun :- 2,869
Million Kms.
• Extremely cold Atmospheres
• Revolution Motion :-84 years.
• Rotation Motion :- 17 Hrs. 14
Min
• Numbers of Satellites :- 17
• Uranus has an axial tilt of
97.77°, so its axis of rotation

NEPTUNE (VArUN)
• This Planet was discovered
by Urbain Le Verrier in
1946.
• Distance ( From Sun) :- 4496
Million kms.
 Revolution Motion :- 164
years.
• Atmosphere is Composed of
79 % Hydrogen 18 % Helium
and 3 % Methane.
• That’s Why this Planet looks

METEOrITES & METEOrS
• Small pieces of
• When meteoroids
space debris usually
enter the Earth's
parts of comets or
atmosphere they are
asteroids)that are
called meteors.
on a collision
course with the
Earth are
called meteoroids.

WHy DO METEOrS HAVE A STrEAk
OF LIGHT??

• As they travel through our
atmosphere, meteors collide
with air molecules that knock
away materials and strip
electrons from the meteor…
• When the stripped atoms
recapture electrons, light is
emitted…
• The color of the light depends
on the temperature and the
material being “excited.”

ArE ALL METEOrS THE SAME COLOr??
• The material or element that makes up a meteor
is the main factor that determines the color of its
glowing trail…
- Sodium = orange-yellow
- Iron = yellow
- Magnesium = blue-green
- Calcium = violet
- Silicon = red

SPOrADIC METEOrS
• These are the meteors that can be seen on any
given night
• They are not associated with any particular
meteor shower
• They come from random directions in the sky

COMET
• A comet is an icy small Solar System
body that, when passing close to the Sun,
heats up and begins to outgas.
• Comet nuclei range from a few hundred
metres to tens of kilometres across and
are composed of loose collections of ice,
dust, and small rocky particles.
• The coma and tail are much larger, and if
sufficiently bright may be seen from the
Earth without the aid of a telescope.
• Halley's Comet is short-period
comets and is visible from Earth every
75–76 year

FAMOUS COMETS
S.NO.

NAME OF THE
COMET

YEAR OF
OCCURANCE

FIRST
DISCOVERED IN
THE YEAR

1

COMET
HALLEY

76.3

1066

2

GREAT COMET
OF 1811

3000

1811

4

COMET MRKOS

5.3

1957

5

COMET
KOHOUTEK

75000

1973

6
7

WACHMANN
HOLMES’
COMET

16.2
7.0

1925
1889

Astronomy

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