This is the first of a 4-part series on Astronomy and stars and asterisms being followed by in Indian astrology.
From time immemorial man has been intrigued by the
splendour above in the night sky; it still interests him. While the Sun and Moon
themselves were a mystery, supernovae terrified him. Meteor showers scared him.
Solar eclipses worried him. Lunar and Solar eclipses, he was convinced, were
the handiwork of some evil forces. Stars were linked to death, birth, seasons,
agriculture and calamities. For some, they were gods and goddesses.
What we see up above is the Universe or Cosmos; a
small part of it, to be precise. All objects in the Universe including our
Earth are floating and moving because of some mysterious force. Science gives
some explanation, but mankind still has to learn a lot.
Even before modern gadgets were invented, people had
identified many stars and planets. Arabs, Indians, Israelis,
Mesopotamians/Sumerians, Babylonians, Mayans, Incas, Africans, Greeks, Romans,
Maoris, Europeans, Australians and Americans all had been stargazing –and even
worshipping stars - for millennia. While these stars were used by all for
voyages, the Arabs used it heavily for travel in the deserts too. Many names of
stars you hear now are in Arabic.
Hipparchus (190-120 BCE*) of Nicaea, Turkey is
considered the greatest ancient astronomer, according to western historians of
science. Though he believed the Earth was at the centre of the Cosmos, his
calculations were very close to modern values. Looking at the sky with his bare
eyes, he created a catalogue of 850 stars in 129 BCE and divided them in to six
magnitudes based on brightness – from the faintest to the brightest.
Astronomers and Theories
Ancient civilizations were convinced that the Earth
was at the centre of the Universe; Modern scientists call this geocentric (geo=pertaining
to the Earth) theory. Indian astrology
still depends on geocentric theory but ‘predictions’ are based on the Moon’s
movement. In Europe, those who knew that the Sun was at the centre of the solar
system (the heliocentric theory; Helios = the Sun) were tortured and humiliated
by the church.
Indian astronomers, many of them followers of the
geocentric theory, had contributed to the development of Astronomy because of
their knowledge of Mathematics. Aryabhatta (5th Century CE), who changed the
Indian concept by propagating the heliocentric theory, deserves special
mention. Other Indians who worked on astronomy are: Lagadha, Varamihira,
Bhaskara I, Bhaskara II, Brahmagupta, Mahendra, Neelkantha, Achyut Pisharody
etc. The Lunar calendar was in vogue in India as early as around 1500 BCE. Saptarshi
calendar has been traced to about 7,000 BCE. But they ended up being misguided on crucial
facts because of their obsession with linking everything to religion and
rituals. Shwetambara sect of Jainism too worked on the sky and stars – there
were about 50 books authored by them. There were siddhantas (Theories or
Treatises) written by Pitamaha, Surya, Vyasa, Atri, Vasistha, Kasyapa,
Parasara, Narada, Garga, Manu, Marichi, Lomasa (Romaka), Angiras, Bhrgu,
Paulisa, Chyavana, Yavana and Shaunaka but only five are available. Siddhantas
of Surya, Vasistha, Pitamaha, Paulisa and Romaka are found in Panchasiddhanta
by Varahamihira (circa 578 CE). The Vedas mention 27 Nakshatras
(stars or asterisms) and 5 planets.
Both Ramayana and Mahabharat, Indian
epics, contain reference to stars. Mahabharat, the story of a war of
cousins, is believed to be about 5,000 years old. The war might have been
fought between 1924 BCE and 3711 BCE, according to some historians, based on
astronomical calculations.
Surprisingly, while they lavishly praise Hipparchus,
the westerners play down the Indian achievements; in many works of modern
scientists and science writers you would not find any mention of the ancient
Indians.
Some references to stellar positions in vedas,
the early Indian scriptures, take Indian astronomy to 4500 BCE. For 2,500 years
between 2000 BCE and 500 CE, Indians had found the circumference of the Earth,
rotation of the Earth, calculated the distance to the Moon, studied about
eclipses which all led them to the conclusion that the Sun, not the Earth, was
the centre of the planetary system. They had also basic information about
gravitation. Many, before and after Aryabhatta and Varahamihira, had done
researches worthy of scientific scrutiny. There were errors, some very
marginal, but the relevance of their efforts cannot be ignored. Many of their
works were taken to the Middle East and ancient Persia. Western writers like
David Pingree think it happened vice versa. There were imports of information
too from these areas. Books like Aryabhatteeya, Bramhsphutasiddhanta,
Siddhanta Shiromani, Brihatsamhita etc enriched Indian astronomy. The
ancient Nalanda University had a separate department Khagola teaching
astronomy (Khagola Sastra) where Aryabahatta is believed to have had his
education. Two centuries before calculus was invented in Europe, Indian
astronomers were using pi (π) and trigonometry.
Many puranas described Mahameru (Tibetan
mountains?) as the centre of universe. This concept gradually changed during
the first millennium of CE.
There were observatories too. Besides the ancient
universities, modern Indian rulers also encouraged study of astronomy. Jantar
Mantars are 5 observatories of 18th century. There is a chapter on astronomic
instruments in Brahmasphutasiddhanta. (See Michael Wood’s BBC
documentary ‘Story of India’-part 4). Water Clock, Gnomon, Star clock etc were
used by Indians over 2000 years ago.
Modern Indian observatories are located at Kodaikanal
(Tamil Nadu), Hyderabad (Andhra Pradesh) and Naini Tal (UP).
Dr. Vainu Bappu, from Tellicherry, Kerala, is regarded
as the father of modern Indian astronomy.
Other modern Indian
astronomers/physicists include Nobel laureate S. Chandrashekhar, Jayant
Narlikar, E.C.G. Sudarshan, A.L. Narayanan, A.K. Das, Jaswant Yadav etc.
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| Dr. Vainu Bappu |
The ‘astronomy-laced astrology’ (Jyotisha Sastra)
was practiced by Indians for over 3500 years. There is a saying in Sanskrit
that ‘whatever you see is the Sun, the Sun, the Sun! (Sarvadarshanam Suryah,
Suryah, Suryah)’. Or simply put, it is the Suns that you see all around.
Incidentally, planets also were treated as stars.
The seven sages (Saptarshis), King Dhruva,
Rohini, Ardra, Agasthya.... all these divine beings and saints of Indian
mythology have representations in the sky. Many books and documentaries are
available on the subject. This article is no substitute for them. Its purpose
is to give a basic understanding of some of the heavenly objects widely talked
of by Indians.
Nakshtara means star in astronomy, but in Indian Astrology,
it refers to one of the asterisms (small group of stars) of 27 divisions of the
lunar zodiac (rāshi). ‘Zodiac’ is the Greek term for ‘circle of stars/animals’.
Origin of Universe and Galaxies
Cosmology is the
science that deals with the origin and evolution of the Universe. It is believed that the Universe was formed
out of a big explosion, referred to as the big bang, 13.77 billion years
ago. That is why scientists say the Universe began with a ‘singularity’ – born
from a single point (in space and time). Ancient Indians, who too had a similar
theory, believed the sound of explosion – ‘Aum’ – was something special. They
called it the pranav mantra, an integral part of Hinduism’s ritual
hymns. The Big Bang’s singularity concept is being seriously challenged by many
scientists.
There are many
theories about the origin of the Universe. Scientists are like economists. One
comes out with a theory, another refutes it.
Galaxies
Galaxies
What looks like a star in the night sky may be a
distant galaxy – or accumulation of stars. A galaxy can be called a
‘sub-Universe’ or an ‘island universe’. Within a galaxy, there are many stellar
systems like the Solar System. Our solar system is situated in a galaxy called
the Milky Way (Ākāsh Ganga or Ksheerapatham). It is also called
the home galaxy.
The current belief
among scientists is that after the big bang, ‘matter’ (Sansk. Dravyam)
was thrown out in all directions. The ‘matter’ comprising gases and dust
grouped together to form stars and galaxies. Due to various processes,
collisions and gravitational force, the dust and gas eventually
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| Heart (R) and Soul (Left) Nebulae Courtesy: NASA |
They all –
including the galaxies and the strewn matter of dust and gas - are in
continuous motion. They rotate around imaginary axes and are on an endless
voyage, at very high speeds - a kind of dance set to some unknown tune and
rhythm by an unknown. The Sun takes about 225-250 million years to complete one
orbit around the centre of the Milky Way from a distance of about 25,000 light
years. Its speed along the orbital track is about 750,000-800,000 km per hour,
taking the whole Solar System with it! Watch this video: At the same time it is
moving upward at a speed of 25,000 km from the plane of the Milky Way! We
crossed the plane 2 million years ago, according to scientists of Stanford
University. In 16 million years, it will reach a height of 250 million light
years and come down to a position 250 million light years below the disk of the
Milky Way. Then it will move up again. The Sun’s up and down journey will
continue throughout its life. How and why? We will have to wait for answers.
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| Artist's Impression of the Collision (NASA) |
years but other events can interfere with its activity.
The collision will
throw all objects in different directions but scientists hope the Sun will be
tossed away to a new region and the planets and other solar objects will move
with it! Barely half a billion years later, the Sun will start its
self-destruction, expanding to become a red giant destroying the Earth and the
inner planets. (The planets between the Earth and the Sun are called inner
planets. Planets between the Earth and Pluto are outer planets).
Dark Energy, Dark
Matter….
Scientists think if
all the objects in the Universe were attracting each other, causing
gravitational pull, the Universe would not be expanding very fast. There is
some force that counters the gravity which they call the Dark Energy. It
exists throughout the Universe accelerating the expansion. According to NASA,
over 72 per cent of the Universe comprises Dark Energy,
There is a theory
that large part of the mass of the Universe is missing! It does not emit light
and is not visible. NASA says over 23% of the Universe is accounted by Dark
Matter.
These are nascent
topics that scientists are grappling with.
How Many of Them?
There are about
170,000,000,000 (170 billion) galaxies within the observable limits of the
Universe that extends to about 13.77 billion Light Years away from us in all
directions. Our Milky Way contains about 400 million stars (100 billion, says
NASA while 200 billion is the figure in Wikipedia). There could be a minimum of
1,000,000,000,000,000,000,000,000 (1 septillion) stars, say scientists1,
in the Universe (100 billion galaxies, says NASA). It could be more because
some galaxies contain 1 trillion to 100 trillion stars. About 30-50 stars, may
be more, are born every year in the Universe, according to some scientists.
Distance, Width and
Length
The Universe is so
huge we cannot measure the distance in miles of kilometers. Instead, it is
measured in Light Years. A Light Year is the distance that light travels in a
year. The approximate speed of light is 300,000 km per second. In a day, light
travels about 26 billion km and in a year about 9,500,000,000,000 km; about 9.5
trillion kilometers! There is another measure used for objects outside the
Solar System – the parsec. A parsec (pc in short) is equal to 3.26 Light
Years.
The star Dubhe, a
component of the Saptarshi asterism is about 125 million Light Years
away from the Earth. That is about 1,183,000,000,000,000,000,000,000 km away!
Our nearest galaxy Andromeda is 21,000,000,000,000,000,000 km away – that is 21
quintillion km!
Scientists
discovered the most distant galaxy in 2012 – a galaxy designated as ‘z8_GND_5296’
at a distance of 13.1 billion years! What scientists saw was a galaxy as it was
13.1 billion years ago. The light from it light started travelling 13.1 billion
years ago; the universe was just 700-800 million old then!
Our Milky Way’s
spiral disk is 2,000 to 3,000 Light Years thick and over 100,000 Light Years
wide. The Sun is about 25,000 Light Years from the centre of the disk. If you
were to look from above the disk, the Milky Way would look like this:
But within the
Solar System, distance is measured in AU (Astronomical Unit). One AU is the
average distance between the Earth and the Sun; about 150 million km.
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| Courtesy: NASA |
Orphan Stars
In addition to the
stars in the galaxies, there are independent stars too; they are the Orphans or
Outcasts. They are found as far as 100,000 Light Years away from their nearest
galaxies. There may be millions of Orphans in the Universe.
Origin of Solar
System
A mentioned above,
our planetary system with satellites, asteroids and comets was formed around
4.6 billion years ago with the Sun (Sol, in Latin) at the centre. There are now
eight planets, after the International Astronomic Union (IAU) kicked out Pluto
in 2006. The largest planet is Jupiter and the smallest is Mercury. Some of
them have satellites.
Sun Is Small
The largest known
star in terms of radius is VY Canis Majoris, a red supergiant, 3,900 Light
Years away from the Earth. It has a radius 1650 times the Sun’s and is 270,000
times brighter than the Sun. The age of the star is estimated to be 190-240
million years. The alphabets ‘VY’ does not stand for anything. It is just an
entry in the scientists’ catalogue. However, the current largest star may lose its rank as more new stars are discovered. (http://www.universetoday.com/13507/what-is-the-biggest-star-in-the-universe/)
80-150 times more
massive than the Sun, a blue variable Pistol Star, discovered in 1997 (in the
constellation of Sagittarius) near the centre of our Milky Way, is also 200-300 times
bigger. It is 10-16 million times brighter than the Sun. University of Florida
says the star is only 5 to 6 million times brighter than the Sun. Pistol Star is
at a distance of 25,000 Light Years from us but can be seen with naked eye; its
age could be 1.7-2.1 million years (Harvard University). Pistol Star is
the brightest star known in the Universe in terms of light emission. Like all
heavy stars, it will have a million years of life.
Bright Stars
‘Top ten’ bright
stars, as seen with naked eye from the Earth (known as apparent magnitude) are
ranked as under@:
Sirius or Alpha
Canis Majoris or Dog Star (Rudra)
Canopus or Alpha
Carinae or Suhail (Agastya/Velaka$)
Rigil Kentaurus or
Alpha Centauri A or Rigil Kent (Trishanku)
Arcturus or Alpha
Bootis or Haris El Salma (Swati/Chothi)
Vega or Alpha Lyrae
or Harp Star (Abhijit)
Capella or Alpha
Aurigae or Alhajoth (Shadaasya or Brahmahridaya)
Rigel or Beta
Orionis or Algebar (Baan Raja)
Procyon or Alpha
Canis Majoris or Anticanis (Parswan)
Archernar or Alpha
Eridani ( Nadeemukha or Matsyamukha)
Betelgeuse or Alpha
Orionis or Al Mankib (Ardra/Athira)
@Sanskrit in blue, Malayalam in
green
What stars are the
brightest in the Milky Way? Tim Thomson3 lists them:
Pistol Star
Cyg OB2#12*
HD93129A
Eta Carinae
QPM 241
HDE319718
HD93129A
*On the basis of
some complex criteria, Cyg OB2#12 can replace Pistol Star as the winner
Tim Thomson says
University of Florida has come out with a new champion, LBV 1806-20, a blue
variable, which may be as bright as 40 million Suns. It is about 150 times
bigger too. But we cannot see it because it is on the other side of the Milky
Way, 45,000 Light Years away. The Pistol Star is only is 5-6 million brighter
than the Sun.
There is a
suggestion that a star, R136a1 at the centre of Tarantula Nebula is the
brightest in the Universe. It is claimed to be 8.77 million times brighter than
our Sun.
What lies beyond
13.77 billion Light Years? Gas and dust as well as galaxies, young and old, and
stars in making, fully developed stars – or all probably young! There may be a
boundary for our Universe; or there may not! Science has not given us an answer
so far.
Meteoroids,
Asteroids and Comets
Meteoroids are rocks up to
around 10 meters in size. They belong to the solar system. Larger ones are
called asteroids. When an asteroid or meteoroid enters the Earth’s atmosphere
and burns up, it is called meteors. If it falls to the ground, it is called a
meteorite. Hundreds of meteors burn up in the Earth’s atmosphere every year.
Asteroids are rocks that
circle the Sun like planets do. They are also called mini-planets or planetoids.
There is an elliptical belt of asteroids about 300 million km away from the Sun;
it is between the orbits of Mars and Jupiter. There are thousands of them in
the belt. About 20,000 are
catalogued. An asteroid Ceres or Minor Planet 1, is
almost one-fourth the size of the moon. It has a rotation period of over 9
hours and circles around the Sun in over 4.5 years. NASA’s Shoemaker spacecraft
landed on Ceres in February, 2001. If they (“the killer asteroids”) slip in to the
Earth’s gravity and eventually crash, there will be enormous damages – like the
crash that killed dinosaurs and caused extensive destruction of life 65 million
years ago. Another asteroid Minor Planet 3, also called Vesta, can be seen with
naked eyes! Scientists believe asteroids are remnants from the time of
formation of the Solar System. All these asteroids put together would have
formed a planet, half the size of the moon. It was Jupiter’s gravitational pull
that thwarted it. All the asteroids do not follow the ‘specified’ path between
Mars and Jupiter. There are ones with chaotic orbits.
Comets are ice rocks
consisting of frozen water, gases and dust. They have regular and irregular
paths around the Sun. Remainders of outer planets or cosmic leftovers, they are
as old as the Solar System. As a comet approaches the Sun, it vaporizes forming
a small atmospheric region called the coma around its core. The dust particles
form a tail, extending to millions of kilometers. The core is called the
nucleus. The coma’s diameter can be as long as 100,000 km. (The Moon’s diameter
is only 3,500 km). There are long-period comets (orbital periods-over 200 years
for circling around the Sun) and short-period comets (orbital periods-less than
200 years). Comet Haley is the most famous comet that visits the Sun every 76
years. Another one, the Shoemaker-Levy, crashed in to Jupiter in 1994. Oort’s cloud, almost on the edge of the Solar
System, is home to millions of comets. The cloud is thought to have a radius of
50,000-80,000 AU. But much inside, 30-1000 AU away from the Sun, is another area,
the Kuiper’s Belt, beyond Neptune’s orbit where short-period comets are thought
to come from. Both regions are named after the scientists who discovered them.
Magellanic
Clouds: These are two galaxies – the
Large Magellanic Cloud and the Small Magellenic Cloud – spotted in 1519 by the
Portuguese explorer Ferdinand Magellan (1480-1521).They can be seen with naked
eye in the southern hemisphere. Distances to these galaxies are respectively
160,000 and 180,000 Light Years.
Exoplanets: Planets of stars
outside the solar system are called Exoplanets. Many distant stars have
planetary systems. NASA says there are nearly 900 confirmed Exoplanets.
Exoplanets that are
larger than the Earth but smaller than Uranus or Neptune are labeled
super-Earths. Gliese 677, a 3 star system, in the constellation of Scorpius has
probably about 7 inhabitable planets. The planets circle around the third star
(Gliese 677C).
Why Does A Star Twinkle?
The stars do not twinkle if you view them from Space.
Light from the stars reach us after traveling through different layers of the
Earth’s atmosphere. Light bends slightly when it passes through varying
densities of air. This causes the twinkling. Turbulence in the atmosphere of
stars also causes twinkling which can be viewed from space. This occurs only in
the case of distant stellar bodies, not closer objects like planets or the
Moon; these closer bodies do not have atmosphere either. Stars in the region of
horizon tend to twinkle more because their light has to travel more through the
air to reach us.
Click here to see how the massive star Betelgeuse (Ardra/Athira)
twinkles: http://www.aavso.org/sites/default/files/images/twinkle.gif
There are also stars with fluctuating brightness; they
are called variable stars. This is either due to the changes taking
place inside the stars or due to other objects (companion stars, planets etc
circling around) eclipsing the view from the Earth.
The Starry Realm Is Not Benign
The night sky is a beautiful spectacle from the Earth.
But, “the starry realm is not benign”, says Bob Berman. What will happen to a
man without the usual protective gear thrown out of a space ship? Bernan
describes thus (Astronomy, November 2013):
“Composed mostly of
water, a human body would quickly revert to the universe’s commonest form of H20
(water) – a block of ice. If subsequently stuck by a meteoroid (piece of
any solid object), the body would shatter in to pieces, ……. If the experience
occurred near Jupiter, radiation would sterilize all living tissue. Near white
dwarfs or neutron stars, tidal forces would rip the skeleton to pieces. In the
Earth’s vicinity, the side of the unprotected astronaut’s body facing sunward
would rapidly heat like a microwave to some 2500 Fahrenheit (1200
Celsius), above water’s boiling point. Searing solar ultraviolet rays
–including the fearsome UVC (Ultraviolet rays-short wave) never
experienced on the Earth’s surface – would deliver a painful burn in 20
seconds. A three-minute exposure would cook skin to carbon. Meanwhile being in
space would nullify one’s health insurance….The pressure differential would
force body gases outward; ear drums and eyeballs would pop.”
Note: words added
are in italics
Mercifully, if all this does not take place within
three and half minutes, the astronaut will still be dead – for want of oxygen.
The Celestial Equator
The sky looks spherical to us. Imagine that the Earth is inside this Celestial Sphere (Khagola in Sanskrit) and that there is a circular line in the sky above the Earth’s equator. This line is the
imaginary equator in the sky. It is called Celestial Equator (Khagola Madhyarekha in Sanskrit) that runs from the east to the west. There is another imaginary line running north-south. This is the meridian. Like our equator that divides the Earth in to two hemispheres, the Celestial Equator divides the sky in to two. [(a) the celestial equator (is) the great circle formed by the extension of the Earth’s equator as it intersects with the celestial sphere. The plane of the celestial equator serves as the reference plane for measuring the right ascension (RA) and declination (d) in the equatorial coordinate system…(b) an extension of the Earth’s equatorial plane cuts the celestial sphere and forms a great circle, called the celestial equator1]. A star appears to travel from the eastern horizon to the western horizon. In this journey it has to cross the Meridian. This is because of the Earth’s rotation. The highest point a star appears to reach is called Zenith. That point is on the Meridian. At the opposite end, is the lowest point, Nadir.
The Celestial Equator
The sky looks spherical to us. Imagine that the Earth is inside this Celestial Sphere (Khagola in Sanskrit) and that there is a circular line in the sky above the Earth’s equator. This line is the
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| Celestial Sphere and Celestial Equator |
Zodiac (Rāsi) and Nomenclature
The vast areas of
the sky were divided in to 12 areas by ancient astronomers, based on the Sun’s
movement. Zodiac refers to these imaginary areas. “Early astronomers described
the path in the sky about 9° on each side of the ecliptic (path of the
Sun in the sky or Celestial Sphere), which they divided into 30°
intervals, each representing a sign of the zodiac. Within their geocentric
cosmology the Sun appeared to enter a different constellation of the zodiac
each month, so the signs of the zodiac helped them mark the annual revolution
of the Earth around the Sun. These 12 constellations, also called zodiac signs,
are Aries (ram), Taurus (bull), Gemini (twins), Cancer (crab), Leo (lion),
Virgo (maiden), Libra (scales), Scorpius (scorpion), Sagittarius (archer),
Capricornus (goat), Aquarius (the
water-bearer), and Pisces (fish)”3.
The names of
constellations derived from the patterns that the major stars make. A Zodiac
may contain more than one constellation or group of stars. Now there are 88
constellations, 76 of which lie outside the Sun’s path. (There are only 75 outside the ecliptic. This dispute is because of the constellation Ophiuchus. Read about it in the third article here). Small clusters of stars
are called Asterisms. For the ancient astronomers there were only 48 constellations.
The ecliptic crosses (that is, the Sun reaches) the celestial equator at two
points – on March 20-21 and September 22-23, approximately. These points are respectively
called Vernal (Spring) and Autumnal equinoxes. Spring and Autumn commence respectively
on these days. On the day of the equinox,
one half of the Earth facing the Sun is totally bathed in sunlight. The days and
nights are almost equal.
Since a day is 24
hours long, every 2 hours a zodiac rises in the east (24 hrs/12 zodiacs). The Sun will remain in a
zodiac for about a month. Then it appears to enter the next zodiac. Thus it
enters each of the 12 zodiacs, (or 13 if we include Ophiuchus) completing a year in the process.
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Along the Ecliptic, you can see the solar zodiac starting from Aries, traveling to the west (Stellarium). Below, see the remaining zodiac going west . Images created with Stellarium. Above, you can find the Autimnal (September) Equinox in Virgo and below the Vernal (March) Equinox in Pisces
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The journey of the Moon also
appears to us in the same manner. It travels through the 27 ‘mansions’(lunar
zodiac).
Solar Zodiac:
Aries/Mesha/Medam -
March 21 - April 21
Taurus/Vrishabha/Idavam -
April 22 - May 21
Gemini/Mithuna/Mithunam -
May 22 - June 22
Cancer/Karkita/Karkitakam -
June 22 - July 21/22
Leo/Simha/Chingam -
July 22 - August 22
Virgo/Kanya/Kanni -
August 23 - September 21
Libra/Tula/Tulam -
September 21 - October 21
Scorpio/Vrishchika/Vrishchikam
- October 21 - November 22
Sagittarius/Dhanus/Dhanu -
November 23 - December 22
Capricorn/Makara/Makaram -
December 22 - January 20
Aquarius/Kumbha/Kumbham -
January 21 - February 18
Pisces/Meena/Meenam -
February 19 - April 21 <zodiac>
Note: Western names
followed by names in Hindi/Sanskrit and Malayalam
Lunar Zodiac (in bracket, Malayalam names):
Ashwini (Ashwathi)
Bharani or Apabharani (Bharani)
Krittika (Karthika)
Rohini (Rohini)
Mrigaseersha (Makayiram)
Ardra (Athira)
Punarvasu (Punartham)
Pushya/Pushyami/Tishya (Pooyam)
Aslesha (Ayilyam)
Magha (Makam)
Purva Phalguni (Pooram)
Uttara Phalguni (Uthram)
Hasta (Atham)
Chitra (Chithira)
Svati (Chothi)
Vishakha (Vishakham)
Anuradha (Anizham)
Jyeshtha (Ketta)
Mula (Moolam)
Purva Ashasdha (Pooradam)
Uttara Ashadham (Uthradam)
Shravana (Thiruvonam)
Dhanishtha (Avittam)
Satabhishak (Chathayam)
Purva Proshthapada (Pooruruttaathi)
Uttara Proshthapada (Uthrittathi)
Revati (Revathi)
As mentioned earlier, Constellation is a large
system of stars with an identifiable configuration and Asterism is the
subgroup of stars in a constellation. Big Dipper (Saptarshis) is an
asterism in the constellation of Great Bear (Ursa Major). A zodiac contains a
constellation and many scattered stars. All constellations that appear to lie
on the Sun’s path are zodiac constellations.
Assigning names to constellations started as early as
4000 BCE by Sumerians. Aquarius was named by Sumerians after their god who
pours the water of immortality on the Earth. Ptolemy had plotted 48
constellations during the reign of Alexander the Great of which 47 are still in
use.
Arabs used stars heavily for their travels in deserts
and seas. Many stars have names in Arabic: Betelgeuse, Algol, Deneb etc.
Bayer in 17th century CE started labeling stars based on the descending order of their brightness using Greek letters. The brightest star in Leo is thus called Alpha Leo (Regulus), the next brightest is Beta Leo (Denebola) and so on. John Flamsteed of England suggested numbering stars from west to east. Thus the westernmost star of Centaurus is ‘1 Centauri’. When you read an article on stars, you will find their names under all the three methods - Arabic names (Deneb), Bayer Greek-letter names (Alpha Cygni), and Flamsteed numeric names (50 Cygni).
Bayer in 17th century CE started labeling stars based on the descending order of their brightness using Greek letters. The brightest star in Leo is thus called Alpha Leo (Regulus), the next brightest is Beta Leo (Denebola) and so on. John Flamsteed of England suggested numbering stars from west to east. Thus the westernmost star of Centaurus is ‘1 Centauri’. When you read an article on stars, you will find their names under all the three methods - Arabic names (Deneb), Bayer Greek-letter names (Alpha Cygni), and Flamsteed numeric names (50 Cygni).
There are naming
systems called BD and HD catalogues, a recent development. Modern nomenclature
uses letters, numbers and positions. There is also a Messier catalogue
developed by French astronomer Charles Messier (1730-1817) for non-comet
objects. Some scientists still use the system of Messier, though, officially,
IAU’s numbering system is considered authentic now. The unofficial in-charge of
the sky is the International Astronomic Union (IAU) founded in 1919. IAU, based
in Paris, France, (www.iau.org) assigns
names/numbers for all objects in the sky.
If you have a
software program of astronomy, do a search using any name or symbol or number
known to you to find an object in the Universe. I use Stellarium, a free software. Symbol
of a star is a Greek letter followed by three letters representing the
Constellation to which the star belongs: Alpha Centaurus is α Cen.
HIP: The European
Space Agency collected cosmic data using a satellite called Hipparcos
(1989-1993). The catalogue based on Hipparcos’s data has nearly 120,000 stars
properly numbered. Hipparcos stands for High precision parallax collecting
satellite. The name’s resemblance with Hipparchus may be noted. HIP
27989 is Alpha Orionis or α Ori as per Bayer’s system; its proper name
Betelgeuse.
NGC: New General Catalogue of
Nebulae and Clusters of Stars contains the list of 7,840 deep-sky objects. A
deep sky nebula or cluster of star is numbered using the prefix NGC.
SIMBAD: Stands for the Set of Identifications,
Measurements, and Bibliography for Astronomical Data.
It contains a list of 15 million objects outside the Solar System.
The 24 Greek letters, capital and
small, used earlier for naming stars are:
Α α Alpha, Β β
Beta, Γ γ Gamma, Δ δ Delta, Ε ε Epsilon, Ζ ζ Zeta, Η
η Eta, Θ θ Theta, Ι ι Iota, Κ κ Kappa, Λ λ
Lambda, Μ μ Mu, Ν ν Nu, Ξ ξ Xi, Ο ο Omicron, Π π
Pi, Ρ ρ Rho, Σ σ Sigma, Τ
τ Tau, Υ υ Upsilon, Φ φ Phi, Χ χ Chi, Ψ ψ Psi, Ω
ω Omega
Circumpolar Stars
Unlike stars rising
in the east and setting in the west, there are stars at the poles that do not
disappear at all. Or, some of them are not visible at all. They appear to
travel in small circles over the Earth’s north and south poles and are called
circumpolar stars. This strange behavior is due to the Earth’s journey around
the Sun and precession (explained below).
If a star rises at
7.00 PM in the east, the next day it will rise at 6.56 PM; 4 minutes early.
Consequently, the star sets in the west 4 minutes early. On the third day the
star will rise at 6.52 PM and disappear 4 minutes earlier than the previous day
in the west. Do keep in mind the daily 4-minute change. Laos keep in mind that
every two hours a zodiac appears in the east.
Children have
better vision than adults. After 40, your vision starts blurring. On a clear
night, without the moon, you can see about 7000-9,000 stars in the sky. With a
good telescope you may see about 200,000 stars. With a more powerful telescope
you can see about 15 million stars. Observatories with very powerful telescopes
see billions of stars.
How Large Is the
Solar System?
This raises the
question about the diameter of the Solar System. Ex-planet Pluto’s average distance from
the Sun is about 40 AU. If this is the criterion, the Solar System’s diameter
is about 80 AU. Sedna, suspected to have the characteristics of a
planet, is the most distant object spotted in the Solar System. It is about 960
AU (144 billion km) away from the Sun in which case the diameter of the Solar
System is about 1920 AU. But the Sun’s gravitational pull fades at 125,000 AU;
so 250,000 AU could be the diameter. There is no fixed answer to the question.
The Life Cycle of
Stars
A bit of physics
here. Mass is a word widely used in astronomy. We all study it in schools and
try to forget…. It is inertia, your teacher might have told you. If you spin a
top, it comes to rest after sometime. Unless acted upon by an external force, a
body in motion continues to be in motion. It is this tendency or quality that
is called inertia. Mass is said to be “the
quantity of matter which a body contains”. When a body is pulled by gravity, it
‘gets weight’. The gravity of each body in space is different. If you weigh 60
kg here, you will weigh only 10 kg on the Moon but 1,624 kg on the Sun - the
same body, the same person, the same mass – but you are subjected to different
measures of gravity.
Our Moon is affected by the Earth’s gravitation. In
turn, the Earth experiences the Moon’s gravity too. The pull of the Earth is
more powerful than the Moon’s. The Sun’s pull is still greater. If you double your mass, all these figures mentioned
above will also double. Distance too is a factor, but leave it aside for now.
In Space, you feel weightless (needs
advanced reading); your weight is zero, you still have inertia and hence
mass. Confused? Don’t worry, even a brilliant scientist cannot define Mass, according to
scientists themselves.
The Sun contains 99.86% of the mass in the solar system! Its
mass is 1.989 x 1030 kilograms =1,989,000,000,000,000,000,000,000,000,000
kg or 1.989 nonillion kg; about 330,000 times the Earth’s mass. Mass of a star
is always compared with the Sun while preparing its profile.
Like human beings,
stars are born; they live and, after millions or billions of years, die
depending on their characteristics and surroundings.
Stage 1. There are clouds of gases and dust in Space.
Such dense cloudy objects are called Nebulae. Many stars could be born in a
nebula. Turbulent system of the materials in a nebula collapses inward under
its own gravitational pull forming a dense centre called the inner core. This
is the ‘star’ in gestation; it is called a protostar, the equivalent of a
foetus or a child.
Stage 2. The protostar glows suggesting that the inner
temperature is in millions of degrees. The compression continues as hydrogen is
converted in to helium.
Stage 3. Energy is released which reduces the speed of
contraction. The protostar shines and now it is called Main Sequence Star (MSS). The Sun is a MSS. A
Sun-like star stays in this state for billions of years till all the hydrogen
available becomes helium.
Stage 4. The
helium core contracts; reactions outside the core are hectic
Stage 5. Carbon is formed from helium
Stage 6. The outer layers get heated due to the
burning of whatever hydrogen left and start expanding. The star is now called
Red Giant. The Sun will be a red giant 4.5 billion years from now
Stage 7. The gases and dust that surround the core
spreads to form Planetary Nebula
Stage 8. Three-fourth of the core remains, cools,
starts fading and becomes a White Dwarf
Stage 9. Once the shining stops, it becomes invisible
and the star is now is called Black Dwarf. This is but hypothetical
A star, bigger than
the Sun (1.5 to 3 times the Solar Mass), explodes in less than second at the end of its Red Giant
stage in a massive display outshining even its own galaxy briefly. This
explosion is called Supernova. If the core does not get destroyed in the
explosion it turns in to a small Neutron star. When a Neutron star, hardly 10
km across, emits radio waves, it is called Pulsar. If the star’s mass is over 3
times the Solar Mass and the core continues to exist even after the explosion,
it contracts to become a Black Hole. We still know very little. The black holes
are fearsome ‘entities’ with intense gravitational force gobbling up everything
around them. Even light entering it cannot come out. Some scientists have even
wondered if our Universe itself is inside a black hole!
The whole processes from birth to death last billions
of years. In about 5 billion years, the Sun will become a Red
Giant, its radius becoming 100 times longer than it is now. Its outer layer
will be beyond the Earth’s orbit. The
Earth will get vaporized. Distant planets like Uranus and Neptune may become
hospitable and man will have migrated to those planets by then.
Wolf-Rayet stars represent a final burst of activity before a huge star
begins to die. These stars, which are at least 20 times more massive
than the Sun, “live fast and die hard”, according to
The final stages of a star depend on its size; like yellow dwarf, red dwarf, red giant and super dwarf (Read NASA’s article4 for more information):
NASA(3a).
The final stages of a star depend on its size; like yellow dwarf, red dwarf, red giant and super dwarf (Read NASA’s article4 for more information):
Our Sun, a yellow
dwarf star, is 5 billion years old and will die in another 5 billion years provided our Milky Way galaxy does not crash in to
Andromeda galaxy in 4 billion years from now. In that case, who knows, the Sun
may not be there to perform the final rituals of its life! For the time being,
we are safe!
The colour of a star depends on its surface
temperature. The following data in Kelvin scale (apprx.) may be helpful:
(Kelvin scale in degrees (K) = Temperature in 0C
+ 273)
11,000+ Blue
(Sirius, Spica, Rigel, Vega)
6,000-7,500 Blue to White (Canopus,
Procyon)
5,000-6,000 White to Yellow (Sun,
Capella)
3,500-5,000 Orange to Red (Arcturus,
Aldebaran, Betelgeuse)
Below 3,500 Red (Betelgeuse, Antares)
If a star’s
temperature is about 4,0000C, it is more yellowish than orange.
(Mars is a red planet because the iron content on its surface reflects
sunlight). Our Sun’s surface temperature is only 5,8000K. Towards
the evening of its life a star may have orange or red color. Betelgeuse, a
supergiant and a favourite of Indians, is an old hand, estimated to be about
400 to 600 Light Years away– it will die in about 1,000 million years, a short
time in Cosmology. It may become a black
hole. The resultant supernova may not harm the Earth. Scientists say the Earth
will be affected only if a supernova occurs within 50 Light Years -
approximately 11,350,000,000,000 km or 11.35 trillion km.
A very large supernova (of a star greater than 30 times the Mass of the Sun) involving large quantum of energy - perhaps next only to the Big Bang - is called a Hypernova. It is also called a 'collapsed star' or 'Collapsar'.
A very large supernova (of a star greater than 30 times the Mass of the Sun) involving large quantum of energy - perhaps next only to the Big Bang - is called a Hypernova. It is also called a 'collapsed star' or 'Collapsar'.
How to measure the
brightness of a star?
Most of the
articles on brightness in newspapers and periodicals as well as in the internet
tend to be esoteric. It is very difficult to find one for common man. What all a common
man wants to know is ‘if he keeps a distant star, say X, and the Sun side by
side, how many times will X be brighter than the Sun?’
Luminosity is the only
option. In this method, the Sun’s brightness is treated as 1. If the value of
luminosity for X is 100, it means X is 100 times brighter than the Sun; It is
like comparing 1 Watt bulb with a 100 Watt bulb. Leave aside how luminosity is
calculated.
(The symbol for
luminosity is ‘L’ followed by the symbol ‘ʘ’ as subscript. The symbol ‘ʘ’
- a dot inside a circle - represents the Sun. Luminosity of Pollux is 43 Lʘ.
This means luminosity of Pollux is 43 times the luminosity of the Sun.
Similarly, ‘R’ followed by ‘®’ refers to the radius of the Sun. The radius of
Pollux is approximately 9 Rʘ. It means radius of Pollux is 9 times
the radius of the Sun. Similarly, the Sun’s mass is the standard for comparing
masses of objects in the universe. This value is represented by Mʘ).
Unfortunately, the exact
of luminosity of stars is not reliable; charts show different figures for the
same star due to limitations faced by scientists. . Because of the difficulty
in measuring luminosity of stars, one star can have different values. E.g.,
Aldebaran’s luminosity is shown 200 to 700 (times the Sun’s) in different
articles.
When you read about
comparative brightness, take it tentatively. There is a list of 500 bright
stars or the ‘500 club’ that we can see at night with naked eye. The 500 club
includes stars whose apparent magnitude is 4 or less. The list is topped by
Sirius, also called Alpha Canis Majoris with an apparent magnitude -1.44. The
500th star is Acamar or Theta Eridani (3.97). Thanks to www.astrostudio.org for this list - it
helps a beginner and an expert alike.
Wobble of the Earth
(Precession)
The Earth with a
circumference of about 40,070 KM (25,000 miles) rotates at a speed of over
1,600 KM (1,000 Miles) per hour. Its speed of journey around the Sun is over
100,000 km per hour. All the action is not as steady as you think. The Earth
sways; its orbital speed varies.
When a toy top
spins, it is not doing it at perpendicular to the plane. There is a sort of
circular swaying like a dancer. The Earth too does it while it spins around its
imaginary axis. This swaying is called wobble or precession. See the
diagram (below) from www.mydarksky.org.
The Earth’s axis,
now points at Polaris (Dhruva). Hence it is called the polar star. The
‘Pole’ position changes by 10 during a period of over 71 years
approximately. Since the circle of precession covers 3600, you can
calculate the approximate time required for completion of one full
circular movement of the pole (71x360). It lasts about 26,000 years which is
called a Great Year or Platonic Year. Watch this video clip
(animation) from Aryan Navabi: http://www.youtube.com/watch?v=82p-DYgGFjI
.
Circa 8000 BCE, Tau
Herculis (Constellation Hercules) was the pole star. By 18400 CE it will be
back again.
About 5,000 years
ago Thuban (Alpha Draconis in Constellation Draco, the poisonous serpent) was
the pole star; later it was Kochab (Beta Ursa Minoris of Little Bear
constellation). Thuban will become the pole star again in 20346 CE.
After 13,000 years
Vega (Abhijit) will be the pole star. ‘Now scientists attribute the
wobble to a shifting surface caused by seasonal variation’5. The irregular distribution of mass within the Earth
plays a role; so do the gravitational forces of the Sun, Moon and other
planets.
You
will see a very useful animation here: http://www.themistsofavalon.net/t4070-the Earth-wobble?highlight=wobble;
the wobble will appear only if you log in. Registration is free.
It is interesting to read more on the causes and
effects of wobble. One notable change was a ten day-correction while shifting
from Julian to Gregorian calendar: what followed October 04 in 1582 CE was not
October 05, but October 15.
Can a planet fall
in to the Sun?
The sun’s
gravitational force is mighty. All bodies circling it including the Earth should
fall in to the Sun. But they cannot. For example, the Earth travels at over
100,000 km per hour. As it moves at great speed, the gravitation of the Sun
tries to pull it, but the Earth’s speed is just enough to resist this pull; at
the same time the speed is not good enough to escape from the grip of the Sun.
So it keeps moving around the Sun. The same principle applies to the Moon. It
cannot fall in to the Earth. And the Sun
itself will not fall in to the centre of Milky Way because of its speed. All
objects in the universe circling around a star or centre of a galaxy remain in
their orbits because of this phenomenon. (Just to remind you, the galaxies are
travelling in all directions at high speeds away from the point from where they
originated after the big bang).
End of the Universe
Well, the Universe
had a beginning. It should have an end too. ‘The Universe may one day
collapse and everything in it – including the Earth – will be compressed in to
a small, super hot, hard ball, scientists have warned.
‘The risk of a collapse is even greater than previously thought and the
process may have already started somewhere in the universe, scientists claim’.
The news comes from the University of Southern
Denmark. Everything in the Universe will become millions of times heavier than
it is now. The weight will squeeze all
material in to a super hot, super-heavy ball and that’s it – the end of the
Universe. This implosion is called the phase transition.
The Moon and the Rāsis
The Moon is the
brightest object in the night sky. It is about 384,000 km (average distance)
away from us. It is believed to have formed about 4.5 billion years ago from a
large chunk of the Earth was ripped off following a collision with an object as
big as the Mars. The gravitational pull of the Earth made the chunk circle
around the Earth. Named the Moon, it thus became our only natural satellite. It
reflects sunlight that gives it the sheen. Actually the Moon’s surface is dark.
Tides are caused by the gravitational effect of the Moon. Its radius is 1,738
km. When it comes between the Sun and the Earth at a particular distance, it
covers the solar disc fully causing Solar Eclipse. When the Earth comes in
between the Moon and the Sun at a particular distance covering the Moon’s disc
fully, total Lunar Eclipse occurs. The eclipses can be partial, if the the
Sun’s/Moon’s disc is not fully covered. All astrologers get busy when total or
partial eclipses occur. There were manned and unmanned missions to the Moon.
India’s spacecraft (Chandrayaan mission, 2008) helped find presence of
water ice close to the surface at the lunar poles. We always see only one side
of the Moon because the time it takes for one rotation about its axis and the
time to orbit the Earth are the same – this phenomenon is called ‘synchronous
rotation’.
Indian vedic astrology follows the sidereal (Latin
‘sidus’ means star) time while western astrology follows the solar time.
Sidereal time ‘is the time measured based on the earth’s rotation relative to
fixed stars’. The solar time is based on the position of the Sun.
Between two full moons, there are 29.5 days. But the
Moon takes only 27.32 days to move around the Earth. The difference arises
because of the Earth’s forward motion; the moon tries to catch up with it and
in the process covers over 3600. One needs to go deeper to
understand the difference between the two systems of measurement.
The Moon is actually moving away
from us. Scientists have estimated that it is moving away from us approximately
3.8 cm per year! It will not desert us though – before that happens the mighty
Sun, in its final stages of life, will expand and destroy the Earth and the
Moon, as mentioned earlier (see ‘Life Cycle of Stars’ above). It seems to be a
pact between the Moon and the Earth – ‘till death do us part’! And the latest
discovery is that the Moon is shrinking like a grape! Its interior has been
cooling and it is now 150 ft smaller (https://scitechdaily.com/our-moon-is-shrinking-generating-wrinkles-and-moonquakes/).
The Moon’s path in
the sky is crucial for Indian astrologers. Our forefathers initially thought it
took 28 days for the Moon to circle the Earth, as mentioned in Atharva Veda
. The Moon’s path around the Earth is called the Moon’s trajectory which is
very close to the ecliptic. This lunar path, covering 3600, was
divided in to 28 areas. The areas containing these asterisms were called rāsis
(lunar mansions or lunar zodiac). The concept of single star does not exist in
Indian tradition, with a few exceptions though. Once the Moon’s orbit was found
to be 27.322 days long, one star or asterism had to be dropped. The axe fell on
Vega (Abhijit) which was a small rāsi between Uttara Āshādha/Uthradam
and Shravan/Thiruvonam. The Moon, during its circular journey,
passes through each of these asterisms – nakshatras – in 27.322 days,
i.e. 13.330 per day i.e. the Moon will reside in a nakshatra
for 24 hours. During its journey, the
Moon’s position in these asterisms is verified. Each of those stars/asterisms
within the Moon’s trajectory or close to it is considered nakshatra
which is an area or mansion measured in degrees. The rasis bear the
names of the nakshatras. Only 12 of these nakshatras have full
moons (pournamis). These 12 months in Indian calendar are named after
these nakshatras. This method is mentioned in Vedanga Jyotish
(part of Rig Veda and Yajur Veda).
All the 27 nakshatras/stars
are females, born to Daksha, a procreator (Prajāpati) in Hindu
mythology. All are married to Chandra, the Moon god. There are different
versions about the birth of the Moon god. One of them is that he rose from the
cosmic sea that was churned by the divine beings and demons jointly to get the
holy nectar that was believed to bestow eternality. Another story says he was
born of tear drops of sage Atri. The Moon god is the deity of herbs.
In Stellarium
you can track the Moon on each day (by using the date manipulation option) and
find in which constellation it is and which nakshatra is close to it.
Amateur Astronomers
There are more
terms (Apparent Magnitude, Absolute Magnitude, Bolometric Magnitude, Variable
Star, Declination, Right Ascension, Spectral Type, Meteor Showers etc.) to be
learnt, but they are for serious students of astronomy. If you are a serious
student, you may contact the science departments of your nearest college,
planetarium, amateur astronomers or associations of amateur astronomers in your
area.
Follow the Stars
Before we start
note the following:
The software Stellarium
referred to earlier is freely available in the net. You can select in it a
single constellation or more for viewing. There are many settings which you can
make use of without any training.
After installing Stellarium,
set your location by entering its longitude and latitude. Many major Indian
locations are listed in the software. If not, check in www.wikipedia.com to see if there is a write-up
on your location. In case longitude and latitude are not mentioned in
Wikipedia, you can find the location – village or town or suburb or a nearby
place - using any search engine. One of the sites that you may get the
information from is www.heavens-above.com . Stephen Hughes’s
guide of Stellarium will be of great help you6.
Stargazing
Since this article
carries only the very basic information, a few constellations relevant to
Indians alone will be discussed.
The position of
stars changes every night. The time for viewing various constellations in India
is:
Months Major
Asterisms (not all listed)
December, January,
February Orion,
Taurus, Aries
March, April, May Gemini,
Leo, Cancer
June, July, August Scorpius,
Sagittarius, Virgo, Libra
September, October,
November Pegasus,
Pisces, Aquarius,
Capricornus
If you have any
star chart (normally published by newspapers at the start of a month), keep it
above your head, with the chart’s north facing the Earth’s north.
Note that the Sun’s
radius is about 700,000 km (435,000 miles). The size of stars referred to here
is based on radius. Also note that in the Bayer pattern of naming, a Greek
letter followed by genitive (possessive case) forms is used. E.g. Arietis for
stars in Aries, Orionis for Orion etc.
Under each
Constellation, its symbol is given. Non-traditional constellations do not have
symbols. But Denis Moskowitz has designed symbols for many such constellations
(www.suberic.net). His symbols are used for
the non-traditional constellations.
Although the first
zodiac is Aries/Mesha/Idavam, we may start with the constellation
of Orion (Mriga or Mrigavyaadha/Makayirram-Athira group)
which can be very easily identified and then move on to nearby constellations.
As far as the position of the stars is concerned, some follow a realistic
method by locating the current position of nakshatra with reference to
the Moon’s path and the distance between two nakshatras; after all, the
area available is only 3600 to accommodate 27 nakshatras.
There are many opinions about what stars represent nakshatras. An Expert’s
Opinion is also added wherever a single star can be picked as a Nakshatra.
This is based on the data collected by me from various sources over a period of
time.
Whatever described
in the next few pages could have been presented as a chart. But descriptive
information is more likely to be registered in memory than data in grids.
The Sun is not
dealt with separately as information about it is mentioned throughout above.
********************
References:
*BCE
= Before Common Era (used in place of BC); CE= Common Era (used in place of AD)
$ Velaka -The
meaning of this Sanskrit (?) word is not available in the dictionaries I referred to
Cont'd >>Page 2
- Encyclopedia of Space and Astronomy – Joseph A. Angelo Jr.
- http://www.universetoday.com/102630/how-many-stars-are-there-in-the-universe/www.tim-thompson.com
- http://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve/
3a: http://www.universetoday.com/24736/wolf-rayet-star/ - http://cms.qut.edu.au/__data/assets/pdf_file/0005/24098/Stephen-Hughes-stellarium-article.pdf
Cont'd >>Page 2
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