Aryabhata

Considered one of the biggest innovative thinkers and contributors to the Indian history, Aryabhata gave a whole new dimension to astronomy, mathematical rules and propositions.

Born in 476 A.D., in Kerala, the Hindu astronomer Aryabhata studied in Nalanda University near Kusumaputra, now Patna. His only surviving work is amassed in Aryabhatiya, recognized as a masterpiece. His genius led the ruler Gupta to promote him as the head of the University.

Aryabhata was the first to expound that the Earth is round and days and nights are caused because the Earth rotates around its axis. He also rightly explained about the occurrence of the eclipses. According to the Hindu Mythology, solar and lunar eclipses occur because "Rahu" gobbled up the moon and the sun. But he said the eclipses transpired due to the shadows cast by the Earth and the Moon.

His contributions in Mathematics are spectacular and very valuable. He gave the value of (PI) 3.1416, claiming, for the first time that it was just an analogue. It’s believed that he also formulated tables in maths, which later came to be called as the "Tables of Sine". His method to find solution for quadratic equations of the sort: ax(sq.) – by(sq.) = c is also recognized world-wide. He devised a method to write the cumbersome numbers in a poetic form. But this summary is rather complex to grasp. Basically, Aryabhatya dealt with aspects of mathematics, astronomical calculations, geometry, square root, cube root, progression and celestial sphere, all written in Sanskrit in the form of verses. His contribution is so vast that it is hard to write a small gist of the whole thing. In acknowledgement to his contributions in Astronomy and maths, India’s first satellite was named "ARYABHATA".

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The Greatest Historical Astronomers

An interesting book entitled, "Human Accomplishment" by Charles Murray has attempted to select the most important figures in the arts and sciences from 800 BC to 1950 AD. A total of 4002 significant figures were culled from a large number of authoritative sources covering astronomy, physics, mathematics, chemistry, biology, earth sciences, technology, the various arts, and philosophy. Murray used statistical analysis as a guide to avoid selections based on nationality, gender, race, or popularity. I think he did a very credible job in his selection process. The top twenty people were ranked within each class. For example, the two most important figures in physics were Newton and Einstein, in mathematics, Euler and Newton, and in technology, Watt and Edison.

Of the 4002 significant figures selected, 124 were astronomers. 204 were chemists, 85 were in the earth sciences, 218 were physicists and 101 were mathematicians. As for the arts, there were 522 significant musicians and 1128 significant authors.

Here are his top twenty astronomers in rank order with accomplishments:

1.GALILEO Galilei (1564-1642)   

                               

Resolved the stars in the Milky Way, discovered sunspots and measured the Sun’s rotation, observed Venus phases, discovered four moons of Jupiter, observed lunar features and measured lunar wobble, supported the Copernican system of planetary movement via his observations.

2. KEPLER Johannes (1571 – 1630)

Using Brahe’s precise data derived his three laws of planetary elliptical motion, provided explanation of optical image formation through small apertures, the first enunciation of the inverse square law for intensity of illumination.

3. HERSCHEL William (1738 – 1822)

The discoverer of Uranus and several satellites of Saturn and Uranus, discovered that some double stars orbit each other, discovered infrared radiation, attempted to map the Milky Way’s shape, known for building state-of-the-art telescopes.

4. LAPLACE Pierre-Simon (1749 – 1827)

Postulated the solar system evolved from a large flattened cloud of gas, published differential equations describing planetary orbits and tides, determined the masses of Jupiter, Saturn and Uranus, applied probability theory to errors in observations.

5. COPERNICUS Nicolaus (1473 – 1543)

Proposed Earth orbited the Sun via De Revolutionibus Orbium Coelestium contradicting the long held Ptolomic belief that the Sun orbited the Earth thereby laying the groundwork for Galileo and Kepler.

6. PTOLOMY Claudius (2^nd century AD)

Through his Almagest constructed an accurate geocentric model of the solar system consisting of a series of deferents and epicycles that was followed for 15 centuries until Copernicus.

7. BRAHE Tycho (1546 – 1601)

Chronicled supernova of 1572 and discovered it had no diurnal parallax proving it lay beyond the Moon, plotted the motion of the comet of 1577, accurately plotted motions of planets used by Kepler after his death.

8, HALLEY Edmond (1656 – 1742)

Astronomer Royal, discovered Omega Centauri, paid for publishing Newton’s Principia, using Newton’ gravitational law predicted the comet of 1682 would return in 76 years, invented the idea of using transits of Mercury and Venus to determine distance to the Sun.

9, CASSINI Giovanni (1625 – 1712)

Measured Mars and Jupiter rotation periods, first scientific records of zodiacal light, discovered the Cassini division, and investigated atmospheric refraction.

10, HIPPARCHUS of Nicaea(190 - 120 BC)

Founder of systematic observational astronomy, discovered the precession of the equinoxes, confirmed Eratosthenes value for the obliquity of the ecliptic, completed a catalog of 1080 stars.

11, BAADE Wilhelm (1893 – 1960)

Proposed supernova could produce cosmic rays and neutron stars, first resolved stars in Andromeda galaxy, defined Population I and II stars and two kinds of Cepheid variables.

12. HUBBLE Edwin (1889 – 1953)

Discovered the Hubble classification of galaxies, using Cepheid variables in M31 and M33 calculated their distances, showed that galaxy distribution was cosmologically uniform, showed galaxies were moving away from us at speeds proportional to their distance (Hubble’s Law).

13. BESSEL Friedrich (1784 – 1846)

Father of modern astrometry, published first accurate stellar parallax, discovered orbital deflections of Sirius and Procyon from unseen white dwarfs.

14, HUGGINS Sir William (1824 – 1910)

Invented the stellar spectroscope, comparing laboratory and stellar spectra demonstrated that the Orion nebula's pure emission spectra indicated its gaseous nature while Andromeda galaxy had continuous spectra, imaged solar prominences in H Alpha light.

15, HALE George (1868 – 1938)

The first astrophysicist, invented the spectroheliograph allowing photography of solar prominences in daylight, discovered magnetic fields in sunspots, planned and completed the 200-inch Mt. Palomar telescope.

16, EDDINGTON Sir Arthur (1882 – 1944)

An astrophysicist, discovered the stellar mass-luminosity relationship, explained Cepheid variable pulsations and very high densities of white dwarfs, formulated the Eddington Limit which relates star’s maximum luminosity to its gravitational force.

17. HERTZSPRUNG Ejnar (1873 – 1967)

Studied stellar proper motions and motions of binary stars, using photography studied stellar brightness, compared stellar color ratios, plotted color-magnitude diagram for the Hyades cluster, which evolved to the Hertzsprung-Russell diagram. 

18. OLBERS Heinrich (1758 – 1840)

Discovered several comets, searched for missing planet between Mars and Jupiter forecasted by Bode’s Law and discovered Pallas and Vesta suggesting these were fragments of the missing planet, formulated Olber’s Paradox.

19, KUIPER Gerard (1905 – 73)

First planetary scientist, spectroscopically detected CH₄ on Titan and CO₂ on Mars, identified the comet-like debris of Kuiper’s Belt at the edge of the solar system.

20. HEVELIUS Johannes (1611 – 87)

An accomplished instrument maker, introduced the vernier scale for accuracy, developed a catalog of star positions and a celestial atlas, discovered four comets and was the first to observe a transit of Mercury.

Although one could quibble with the rank ordering of these great astronomers, it seems difficult to dislodge any from the list with anybody else. I recommend this book to anyone interested in the arts and sciences.

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The Formation of Galaxies

Theoretical investigations indicate that galaxies formed from a diluted but lumpy mixture of hydrogen and helium gas - the primordial elements forged in the Big Bang. They also indicate that two vastly different scales of mass prevailed less than 100 million years after the Big Bang, which ultimately affected the formation of galaxies. (See the later discussion of dark matter and the formation of structure.)

Two Scales of Matter

Matter either was clumped into vast collections more than a million times the mass of the Milky Way, or into small clumps one million times smaller than the mass of our Milky Way. Superclusters of galaxies may have evolved from the former. Globular clusters such as M15 in the adjacent image may have evolved from the latter.

Results from Recent Observations

As we look deeper into the Universe and therefore back in time, galaxies appear to emit more of their light in the blue part of the visible spectrum. This blue light is a sign that very young, massive and luminous stars are forming (see the discussion of the spiral arms in spiral galaxies, for example). Since we see these galaxies as they were between 5 and 10 billion years ago, we appear to be witnessing events that occurred within a few billion years after these galaxies were formed. Astronomers also have noticed that as they examine the images of these distant blue galaxies, the images are frequently distorted or contain what appear to be multiple nuclei. The Milky Way seen at a similar great distance would look like a uniformed flattened disk, with a single bright nucleus -- the galactic center. Nearby "multiple-nuclei" galaxies that have been studied show the cores of individual galaxies colliding and merging into one single system of stars and gas. These collisions are violent, and take millions of years to play out. But in at least some instances, such as NGC 1275, recently observed with the Hubble Space Telescope, galaxy collisions can actually trigger the formation of massive stars.

Cosmic Cannibalism

In the depths of space, we may be witnessing collisions between smaller galaxies triggering the formation of massive luminous stars. The images, rich in blue light, gives tantalizing evidence that "environment" may have been more important than cosmic "genetics." Galactic cannibalism was far more common in the ancient past. Galaxies may have grown to their current size by consuming their neighbors. The ultimate building blocks may indeed have been the paltry million-solar-mass clumps that theoreticians believe were abundant before the Universe was a few million years old.

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Source:
NASA Space Short
NASA Headquarters
Washington, D.C.
December, 1994

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what are galaxies ?

We assume the stars to be gathered together into galaxies and that these form the basic building blocks of the visible matter in the Universe. Many of the galaxies are similar to our own Milky Way, but many are rather different.
The adjacent image shows the Hubble Deep Field: the Hubble Space Telescope was pointed at the same region of the sky (in the constellation Ursa Major) for 10 consecutive days and images were combined to give the most distant optical view of the Universe yet obtained. In this image, almost every smudge is a galaxy, and objects down to visual magnitude +30 can be seen.
Because looking out to such large distances implies looking back in time because of the finite speed of light, this image is actually giving us a view of the Universe early in the history of galaxy formation. This image may represent what the Universe looked like only a billion years or so after the Big Bang. 

 The Hubble Classification

Galaxies may be viewed as the basic building blocks for the large-scale visible stucture of the Universe. There are may galaxy types, having rather diverse features. Therefore, it is useful to have a way to classify galaxies into different types.

The Tuning Fork Diagram

Hubble introduced the classification scheme illustrated in the following figure, which separates most galaxies into elliptical, normal spiral, and barred spiral categories, and then sub-classifies these categories with respect to properties such as the amount of flattening for elliptical galaxies and the nature of the arms for spiral galaxies. The galaxies that do not fit into these categories are classified separately as irregular galaxies. 

Hubble Classification of Galaxies

This diagram is termed the Hubble classification scheme, or (because of its shape) the "tuning fork diagram". 

Examples of Hubble Galaxy Types

 

Here are some examples of specific galaxies that illustrate some of the Hubble classification types.

• M81: Type Sb spiral
• NGC2997: Type Sc spiral
• M95: Type SBa barred spiral
• NGC1365: Type SBb barred spiral
• Leo I: Type E3 (dwarf) elliptical
• M110: Type E6 elliptical
• Small Magellanic Cloud: Irregular type 

Observation of Galaxies

Many of the more nearby galaxies can be observed through small telescopes.

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What is the age of the universe ?

As we shall discuss further in connection with the big bang, there is strong evidence that the Universe has not always existed, but instead came into being a finite amount of time ago. There are several measures of the age of the Universe. Let us discuss two: (1) the age of globular clusters and (2) the inverse of the Hubble constant. 

Globular Clusters

 

As we have already discussed, the turn-off point for the HR diagram in globular clusters provides a measure of the age of the cluster. Thus, the age of such clusters place a limit on the age of the Universe, for it must be at least as old as the objects that it contains. Such estimates typically yield ages in the range 14-18 billion years 

Hubble Time

 

The inverse of the Hubble constant H has the units of time because the Hubble law is
v = H d where v is the velocity of recession, H is the Hubble constant, and d is the distance. Thus, from this equation, we have that 1/H = d/v. but d/v is distance divided by velocity, which is time (e.g., if I travel 180 miles at 60 miles/hour, the time required is t = d/v = 180/60 = 3 hours).
Thus, the Hubble time T is just the inverse of the Hubble Constant:


T = 1 / H Taking a value of H = 20 km/s/Mly (where Mly means mega-light years),
where all the factors are necessary to convert the time units to years and I've rounded some numbers to simplify the display.
The physical interpretation of the Hubble time is that it gives the time for the Universe to run backwards to the Big Bang if the expansion rate (the Hubble "constant") were constant. Thus, it is a measure of the age of the Universe. The Hubble "constant" actually isn't constant, so the Hubble time is really only a rough estimate of the age of the Universe.
Reasonable assumptions for the value of the Hubble constant and the geometry of the Universe typically yield ages of 10-20 billion years for the age of the Universe. For example, H near 50 km/s/Mpc gives a larger value for the age of the Universe (around 16 thousand million years), while a larger value of 80 km/s/Mpc gives a lower value for the age (around 10 thousand million years). Therefore, we shall take this information, and additional information from other methods to estimate the age of the Universe that we have not discussed, to indicate an age of approximately 15 billion years for the Universe.

The Fate of the Universe

 

The Universe is currently expanding. One extremely important cosmological question is whether this expansion will continue forever. As we shall see later, this is a question that does not yet have a definitive answer. Ultimately, this will turn out to be a question of how much mass is contained in the Universe. If it is below a critical amount, the Universe will expand forever. If it is above the critical amount, the expansion will eventually reverse and the Universe will collapse on itself, leading to what has been termed the big crunch. If it is exactly equal to the critical amount, the expansion will slow, but will only stop after an infinite amount of time. Thus, in this case the Universe will expand forever too.

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Precession of the Earth's Rotation Axis

The Earth's rotation axis is not fixed in space. Like a rotating toy top, the direction of the rotation axis executes a slow precession with a period of 26,000 years (see following figure).

Pole Stars are Transient

 

Thus, Polaris will not always be the Pole Star or North Star. The Earth's rotation axis happens to be pointing almost exactly at Polaris now, but in 13,000 years the precession of the rotation axis will mean that the bright star Vega in the constellation Lyra will be approximately at the North Celestial Pole, while in 26,000 more years Polaris will once again be the Pole Star.

Precession of the Equinoxes

 

Since the rotation axis is precessing in space, the orientation of the Celestial Equator also precesses with the same period. This means that the position of the equinoxes is changing slowly with respect to the background stars. This precession of the equinoxes means that the right ascension and declination of objects changes very slowly over a 26,000 year period. This effect is negligibly small for casual observing, but is an important correction for precise observations.

The Dawning of the Age of Aquarius (Almost)

 

Because of the precession of the equinoxes, the vernal equinox moves through all the constellations of the Zodiac over the 26,000 year precession period. Presently the vernal equinox is in the constellation Pisces and is slowly approaching Aquarius.

The Vernal Equinox

This is the origin of the "Age of Aquarius" celebrated in the musical Hair: a period when according to astrological mysticism and related hokum there will be unusual harmony and understanding in the world. We could certainly use a dose of harmony and understanding in this old world; unfortunately, it is unlikely to come because of something as irrelevant as the position of the vernal equinox with respect to the constellations of the Zodiac.

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10 Strange and Amazing Astronomy Facts

Even though man has studied the heavens for thousands of years, we still know very little about the Universe we live in. And as we continue to learn more, we are consistently amazed, and sometimes confused, by what we learn. Here is a collection of amazing, interesting, and strange astronomy facts, in no particular order.

• Scientists believe that we can only see about 5% of the matter in the Universe. The rest is made up of invisible matter (called Dark Matter) and a mysterious form of energy known as Dark Energy.


• Neutron stars are so dense, that a soup can full of neutron star material would have more mass than the Moon.


• The Sun produces so much energy, that every second the core releases the equivalent of 100 billion nuclear bombs.


• Galileo Galilei is often incorrectly credited with the invention of the telescope. Instead, historians now believe the Dutch eyeglass maker Johannes Lippershey as its creator. Galileo was, however, probably the first to use the device to study the heavens.


• Black Holes are so dense, and produce such intense gravity, that even light can not escape. Theoretical physicists predict that there are situations under which light can escape (which is called Hawking radiation).


• Light from distant stars and galaxies takes so long to reach us, that we are actually seeing objects as they appeared hundreds, thousands or even millions of years ago. So, as we look up at the sky, we are really looking back in time.


• The Crab Nebula was produced by a supernova explosion in 1054 A.D. The Chinese and Arab astronomers at the time noted that the explosion was so bright, that it was visible during the day, and lit up the night sky for months.


• Shooting stars are usually just tiny dust particles falling through our atmosphere. Comets sometimes pass through Earth’s orbit, leaving trails of dust behind. Then as Earth plows through the dust in its path, the particles heat up, creating the streaks in the night sky.


• Even though Mercury is the closest planet to the Sun, temperatures can reach -280 degrees F. Why? Since Mercury has almost no atmosphere, there is nothing to trap heat near the surface. So, the dark side of Mercury (the side facing away from the Sun) is very cold.


• Venus is considerably hotter than Mercury, even though it is further away from the Sun. The thickness of Venus’ atmosphere traps heat near the surface of the planet.

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Why astronomy is cool ?( Five reasons )

Planetary Nebula Mz3: The Ant Nebula

It’s beautiful

 

If you go out on a dark moonless night, you will immediately know what I mean. The Milky Way, stretching its jagged course across the heavens, is quite a sight to behold. The constellations, particularly the winter constellations, have an elegance and familiarity to them. The Moon is also an appealing object, with its ever changing phases and frequent conjunctions with other planets in the sky. Through a small telescope, planetary disks, galaxies, nebulae and open clusters come into view, often startling in their majesty.

Of course, the beauty of the universe is not limited to what is immediately visible to our eyes. Deep space objects, seen through the largest of telescopes, are candidates for some of the most beautiful things ever seen by human eyes. Who could not fail to be impressed by the wonderful Hubble photos of the Crab and Eagle nebulas, or the views of the outer planets and moons from space probes such as Voyager and Cassini? To see for yourself, each day NASA publishes it’s Astronomy Picture of the Day. Few images ever fail to impress.

It’s extreme.

 

Nothing can be taken for granted about space. Most of it is unimaginably cold, interspersed occasionally by blisteringly hot stars with coronal temperatures of millions of degrees. Almost everything is racing around at breakneck speed: barreling through space at velocities of hundreds or thousands of kilometers a second relative to us. That’s enough to cause quite an impact if we were to get in their way. All around us catastrophic convulsions are taking place, with vast explosions and unconscionably high energies. This is a Universe of supernovas, neutron stars, magnetars, pulsars and Gamma Ray Bursts – beams of high energy radiation that would eliminate all life on our planet in an instant were our Earth unfortunate enough to stray too close. Black holes exist that can compress the mass of whole stars into volumes a few kilometers wide, creating gravitational fields that nothing, not even light itself, can escape from.

This is the stuff of childhood fantasies. Superpowers. Forcefields. Instantaneous death. The destruction of worlds. It is no wonder that space features so prominently in the minds of the young.

It ignites our curiosity.

 

Astronomy confronts us with some of the biggest and most challenging problems about the nature of ourselves and the fabric of reality. As a science, it has lead the way in overturning ancient notions of how nature should behave. At one time we believed ourselves to be at the centre of the Universe, with all objects, including the Sun, revolving around the Earth. Astronomers through the ages slowly revealed a different truth. Our star and our home planet are among countless billions in a very ancient Universe. Everything we do ultimately only affects an infinitesimally small piece of real-estate in the cosmos. This discovery, while deeply humbling, is enlightening. It tells us that we will never know everything. Our quest for knowledge is unlimited. We are ants in a cathedral, and what a cathedral it is.

The study of the stars and planets has pushed out the frontiers of knowledge in every direction. It’s contribution to science and mathematics cannot be underestimated. Without astronomy, the modern world as we know it would not exist. Astronomy continues to confound us and guide us right to this day. Gigantic accelerators are busy smashing sub-atomic particles into smithereens to gain greater insights into the nature of matter because objects in space do not always behave the way our current scientific models expect them to. Astronomy has revolutionised our understanding of nature and it will continue to do so.

It tells us about our past.

 

When you look into space, at any star you care to mention, you are looking into history. You are not seeing the star as it is now, but as it was when the photons of light left its photosphere many years ago. If you can find the Andromeda Galaxy in the sky, you are getting a picture of how it looked two million years ago, long before humans ever roamed our planet. The largest telescopes can see back billions of years ago, to galaxies in their infancy, still in the process of being formed.

History is about ourselves, how we got here, why things are how they are. Astronomy opens history even further by explaining the origins of our planet, our sun, our galaxy – even providing insights into our Universe and how it all started some 13 odd billion years ago.

Astronomy is fascinating even when applied to our own modest human story. We have had an intense relationship with the stars and planets for thousands of years. It guided the ancient cycles of sowing and harvesting. It provided the raw material for belief systems, rituals and religions. It contributed to our language. It assisted with navigation and discovery. In living memory, we have witnessed men walking on the Moon and robot probes being flung out of the solar system – events likely to be celebrated for millennia to come. Our relationship with the stars has shaped the culture of today.

It’s our future.

 

Astronomy is important to our future, from the short term to the distant long term. Over the coming decades, private companies will take over much of the heavy lifting formerly associated with government agencies such as NASA and ESA. This will create new jobs and new wealth. Bigger telescopes and better equipment will provide insights into reality that will stretch our technological capabilities. Over the coming centuries perhaps we will explore and colonise deep space for ourselves, using technologies yet undreamt of. In the end, billions of years from now, our sun will expand, frying everything on this planet before diminishing in size itself, its fuel spent, its job done.

Perhaps there is a large asteroid or comet out there in space with our name on it. Perhaps our planet will eventually turn against us, forcing us to find a new home. Perhaps we will find a way to cross the enormous gulfs separating us from other stars in our galaxy. All of these possibilities lead us to the conclusion that the stars will feature prominently in the future of the human race.

Astronomy is available to all, from the small child with his toy rocketship, to the octogenarian peering through her telescope at a crater on the Moon. Few endeavours are so wide in scope, so rich in detail, or so marvelous in implication. I invite you to join in.

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