Nobel 2020

Introduction:                                                                                                                                                                                                                                                                                                                    

Nobel Prizes are awarded in the fields of Physics, Chemistry, Physiology or Medicine, Literature, and Peace. Nobel Prizes are widely regarded as the most prestigious awards available in their respective fields.

Alfred Nobel was a Swedish Chemist, Engineer and Industrialist most famously known for the invention of dynamite. He died in 1896. In his will, he bequeathed all of his "remaining realisable assets" to be used to establish five prizes which became known as "Nobel Prizes". Nobel Prizes were first awarded in 1901.

The prize ceremonies take place annually. Each recipient  receives a gold medal, a diploma, and a monetary award. In 2020, the Nobel Prize monetary award is 10,000,000. A prize may not be shared among more than three individuals.

Three Laureates share this year’s Nobel Prize in Physics for their discoveries about one of the most exotic phenomena in the universe, the black hole. Roger Penrose showed that the general theory of relativity leads to the formation of black holes. Reinhard Genzel and Andrea Ghez discovered that an invisible and extremely heavy object governs the orbits of stars at the centre of our galaxy. A supermassive black hole is the only currently known explanation.

Roger Penrose used ingenious mathematical methods in his proof that black holes are a direct consequence of Albert Einstein’s general theory of relativity. Einstein did not himself believe that black holes really exist, these super-heavyweight monsters that capture everything that enters them. Nothing can escape, not even light.

In January 1965, ten years after Einstein’s death, Roger Penrose proved that black holes really can form and described them in detail; at their heart, black holes hide a singularity in which all the known laws of nature cease. His groundbreaking article is still regarded as the most important contribution to the general theory of relativity since Einstein.

Sir Roger Penrose

Sir Roger Penrose is a British Mathematical Physicist, Mathematician, Philosopher of Science and Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics at the University of Oxford, an emeritus fellow of Wadham College, Oxford and an honorary fellow of St John's College, Cambridge and University College London.

Penrose has made contributions to the Mathematical Physics of general relativity and cosmology. He has received several prizes and awards, including the 1988 Wolf Prize in Physics, which he shared with Stephen Hawking for the Penrose–Hawking singularity theorems, and one half of the 2020 Nobel Prize in Physics "for the discovery that black hole formation is a robust prediction of the general theory of relativity".

Reinhard Genzel and Andrea Ghez each lead a group of astronomers that, since the early 1990s, has focused on a region called Sagittarius A* at the centre of our galaxy. The orbits of the brightest stars closest to the middle of the Milky Way have been mapped with increasing precision. The measurements of these two groups agree, with both finding an extremely heavy, invisible object that pulls on the jumble of stars, causing them to rush around at dizzying speeds. Around four million solar masses are packed together in a region no larger than our solar system.

Using the world’s largest telescopes, Genzel and Ghez developed methods to see through the huge clouds of interstellar gas and dust to the centre of the Milky Way. Stretching the limits of technology, they refined new techniques to compensate for distortions caused by the Earth’s atmosphere, building unique instruments and committing themselves to long-term research. Their pioneering work has given us the most convincing evidence yet of a supermassive black hole at the centre of the Milky Way.

Andrea Mia Ghez

Andrea Mia Ghez is an American Astronomer and Professor in the Department of Physics and Astronomy at the University of California, Los Angeles. Her research focuses on the center of the Milky Way galaxy. In 2020, she became the fourth woman to be awarded the Nobel Prize in Physics, sharing one half of the prize with Reinhard Genzel the other half of the prize being awarded to Roger Penrose. The Nobel Prize was awarded to Ghez and Genzel for their discovery of a supermassive compact object, now generally recognized to be a black hole, in the Milky Way's galactic center.

Reinhard Genzel 

Reinhard Genzel  is a German Astrophysicist, Co-director of the Max Planck Institute for Extraterrestrial Physics, a Professor at LMU and an Emeritus Professor at the University of California, Berkeley. He was awarded the 2020 Nobel Prize in Physics "for the discovery of a supermassive compact object at the centre of our galaxy", which he shared with Andrea Ghez and Roger Penrose. Reinhard Genzel studies infrared- and submillimeter astronomy. He and his group are active in developing ground- and space-based instruments for astronomy. They used these to track the motions of stars at the centre of the Milky Way, around Sagittarius A*, and show that they were orbiting a very massive object, now known to be a black hole. Genzel is also active in studies of the formation and evolution of galaxies.

Black Hole

Black hole is a region of spacetime where gravity is so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.

The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, according to general relativity it has no locally detectable features. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe directly.

Albert Einstein

Albert Einstein was a German-born Theoretical Physicist, widely acknowledged to be one of the greatest Physicists of all time. Einstein is known widely for developing the theory of relativity, but he also made important contributions to the development of the theory of quantum mechanics. Relativity and quantum mechanics are together the two pillars of modern physics. His mass–energy equivalence formula, 

which arises from relativity theory, has been dubbed "the world's most famous equation". His work is also known for its influence on the Philosophy of Science. He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect" a pivotal step in the development of quantum theory. His intellectual achievements and originality resulted in "Einstein" becoming synonymous with "genius".

Amal Kumar Raychaudhuri

Amal Kumar Raychaudhuri was an Indian Physicist, known for his research in general relativity and cosmology. His most significant contribution is the eponymous Raychaudhuri equation, which demonstrates that singularities arise inevitably in general relativity and is a key ingredient in the proofs of the Penrose–Hawking singularity theorems.

Raychaudhuri was also revered as a teacher during his tenure at Presidency College, Kolkata. Many of his students have gone on to become established Scientists.

 Stephen William Hawking

Stephen William Hawking was an English Theoretical Physicist, Cosmologist, and author who was director of research at the Centre for Theoretical Cosmology at the University of Cambridge at the time of his death. He was the Lucasian Professor of Mathematics at the University of Cambridge between 1979 and 2009.

Hawking's scientific works included a collaboration with Roger Penrose on gravitational singularity theorems in the framework of general relativity and the theoretical prediction that black holes emit radiation, often called Hawking radiation. Initially, Hawking radiation was controversial.

 General Relativity:

General relativity, also known as the general theory of relativity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.

Some predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples of such differences include gravitational time dilation, gravitational lensing, the gravitational redshift of light, the gravitational time delay and singularities/black holes.

Einstein's theory has important astrophysical implications. For example, it implies the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars. There is ample evidence that the intense radiation emitted by certain kinds of astronomical objects is due to black holes. For example, micro quasars and active galactic nuclei result from the presence of stellar black holes and supermassive black holes, respectively.

Reference:

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INDIA'S PRIDE ADITYA L-1

Aim and Objectives:

Aditya L -1 was meant to observe only the solar corona. The outer layer of the Sun, extending to thousands of km above the disc (photosphere) is termed as corona. It has a temperature of more than a million degree Kelvin which is much higher than the solar disc temperature of around 6000K. How the corona gets heated to such a high temperature is still an unanswered question in solar physics.

It is actually observed  in Solar Eclipse but from Aditya L-1 we can collect data in real time. The data collected from this instrument would also be used as inputs to climate  modes that is used to predict Earth's atmosphere more accurately than now.

Aditya L-1 with additional experiments can now provide observations of Sun's Corona (Soft and hard X ray, Emission lines in the visible and NIR) Chromophore (UV) and photosphere (broad brand filters). In addition, particle payloads will study the particle flux emanating from the Sun and reaching L-1 orbit and the magnetometer payload will measure the variation in magnetic field strength at the halo orbit around L-1. These payloads have to be placed outside the interference from the Earth's magnetic field and could not have been useful in the low Earth orbit.

 Payloads:

Visible Emission line coronagraph: Corona/ Imaging spectroscopy and spectrometer (1.05- 30 solar radii).

Solar Ultraviolet Imaging Telescope (SUIT): Photosphere and Chromosphere imaging (200- 400nm).

Aditya Solar Wind Particle Experiment (ASPEX): Solar wind/ Particle analyzer Spectrometer (H, Alpha, ions 0.1KeV to 5MeV).

Plasma Analyser Package For Aditya(PAPA): Solar wind/ Insitu measurement (ions 0.01- 25KeV; Electrons 0.01- 3Kev).

Solar Law Energy X-Ray Spectrometer(SoLES): Soft Xray/ spectrometer( 1-30KeV)

High Energy L-1 Orbiting X Ray Spectrometer(HEL10S): High X ray/spectrometer(10- 150KeV).

Advanced Triaxial High Ronation Digital Magnetometer: Measure magnetic field(Range  -256nT to +256nT; Accurate 0.5nT)

Orbit of Satellite:

A satellite placed in the halo orbit around the Lagrangian point 1(L1) of the Sun Earth System has the major advantage of continuously viewing the sun without any occultation or eclipses. Therefore, the Aditya- 1 mission has now revised to Aditya- L1 mission and will be inserted in the halo orbit around the L1 which is 1.5 million km from the Earth.

There are five special points where a small mass can orbit in a constant pattern with two larger masses. Of the five Lagrange points three are unstable and two are stable. These are positions in space where the gravitational force of a body like Sun and Earth produce enhanced regions of attraction and repulsion.

These can be used to reduce fuel consumption needed to remain in position. At the L1 point, the orbital period of the object is exactly equal to Earth's Orbital period.

INDIAN LAUNCHING VEHICLES:

Launchers or launch Vehicles are used to carry space craft to space. India has two operational Launchers, Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV).

GSLV with indigenous Cryogenic Upper Stage has enabled the launching up to two tonne class of communication satellites. The next variant of GSLV is GSLV MK 111, with indigenous high thrust cryogenic engine and stage, having the capability of launching four tonne class of communication satellites.

In order to achieve high accuracy in placing satellites into their orbits, a combination of accuracy, efficiency power and immaculate planning are required. ISRO's Launch Vehicle Programme spans numerous centers and employ over 5000 people.

Liquid propulsion system Centre and ISRO Propulsion Complex, located at Valiamala and Mahendragiri respectively, develop the liquid and cryogenic stages for these launch vehicles. Satish Dhawan Space Centre, SHAR is the space port of India and is responsible for integration of launchers. It houses two operational launch pads from where all GSLV and PSLV flights take place.

PSLV:

 Height- 44cm

 Diameter- 2.8m

 Number of stages- 4

 Left Off Mass- 320 tonnes(XL)

 Varients- 3( PSLV- G, PSLV- CA, PSLV- XL)

 First Flight- Sept 20, 1993.

Challenges:

What makes an Aditya L1 mission challenging is the distance of the Sun from Earth (about 149 million km on average compared to the only 3.84 lakh km to the moon)

The super hot temperatures and radiations in the solar atmosphere make it difficult to study.

NASA's Parker Solar Probe’s January 29 flyby was the closest the spacecraft has gone to the Sun in its planned seven-year journey so far. Computer modelling estimates show that the temperature on the Sun-facing side of the probe’s heat shield, the Thermal Protection System, reached 612 degrees Celsius, even as the spacecraft and instruments behind the shield remained at about 30°C, NASA said. During the spacecraft’s three closest perihelia in 2024-25, the TPS will see temperatures around 1370°C.

Aditya L1 will stay much away and the heat is not expected to be a major concern for the instruments on board. But there are other challenges.

Many of the instruments and their compounds for this mission are being manufactured for the first time in the country, presenting as much of a challenges as an opportunity for India's scientific engineering and space communities. One of the such components is the highly polished mirror which would be mounted on space- based telescope.

Due to the risks involved, payloads in earlier ISRO missions have largely remained stationary in space; however, Aditya L1 will have some moving components, scientists said. For example, the spacecraft’s design allows for multiple operations of the front window of the telescope — which means the window can be opened or shut as required.

Chairman of ISRO:

Full name: Kailasavadivoo Sivan

Born on  14th April, 1957

Previous work: Served as the Director of the Vikram Sarabhai Space Center and the Liquid Propulsion Center.

Born place: Mela Sarakkalvilai, near Nagercoil, Kanyakumari District, Tamil Nadu

Education:      Madras University

                       Madras Institute of Technology( B.Tech.)

                       IISc Bangalore( M.E.)

                       IIT Bombay(Ph.D.)

He is the son of mango farmer and studied in Tamil medium at Government School in Mela Sarakkalvillai. He is the first graduate from his family. He completed his masters in Aerospace Engineering from IISc Bangalore. In 1982, he started working in ISRO for PSLV project. He completed his PhD in Aerospace Engineering from IIT Bombay. He is a Fellow of Indian National Academy of Engineering and Aeronautical society of India. In 2014, he was appointed as director of ISRO's Liquid Propulsion Center and in 2015 as a director of Vikram Sarabhai Space Center. Sivan was appointed the chief of ISRO in January 2018 and he assumed office on 15 January. Under his chairmanship, ISRO launched Chandrayaan 2, the second mission to the moon on July 22, 2019. On 2020, December 30, his chairmanship was extend by a year to 2022 January, his early tenure was up to January 2021.

Reference:

i.       https://www.isro.gov.in/aditya-l1-first-indian-mission_to_study_sun

ii.     https://www.researchgate.net/publication/327675634_Space_System_Architecture_of_India's_Aditya-L1_Mission_to_study_the_Sun

iii.   https://earth.esa.int/web/eoportal/satellite-missions/a/aditya-1

iv.    Wikipedia about Prof Kilasavadivo Sivan.

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Booming of Galaxy

Introduction:

A Galaxy is a huge collection of dust, gas, and billions of stars and their solar system. A galaxy is held together by gravity. Our Galaxy, the Milky way also has a Supermassive black hole in the middle. Sometimes galaxies get too close and smash into each other. Our Milky way galaxy will someday bump into Andromeda, our closest galactic neighbour.

But not to worry.....It won’t happen for about five billion years. Even if it happened tomorrow we might not notice.

Galaxies are so big and spread out at the ends that even though galaxies bump into each, the planets and solar systems often don’t get close to colliding.

The word Galaxy is derived from the GREEK galaxies literally “MILKY’’ a reference to the Milky way. Galaxies range in size from dwarfs with just a few hundred million stars [108] to giants with one hundred million [1014] stars each orbiting its galaxy's center of mass.

Why is it important to understand Galaxy?

Galaxies show us how the matter in the universe is organized in large scales and scientists study how the matter is currently organized and has changed throughout cosmic time.

Galaxy Formation:

The galaxies were more numerous, but smaller, bluer and clumpier, in the distant past than they are today and that galaxy mergers play a significant role in their evolution. At same time, quasars and galaxies that emitted their light when the universe was less than a billion years old so we know that large condensations of matter had begun to form at least that early. Many quasars are found in centers of elliptical galaxies. This means that some of the first large concentrations of matter must have evolved into the elliptical galaxies that we see in today’s universe. It seems likely that the supermassive black hole in the center of galaxies and the spherical distribution of ordinary matter around formed at the same time and through related physical processes.

Dramatic confirmation of that picture arrived only in the last decade, when astronomers discovered a curious empirical relationship: as we saw in Active Galaxies, Quasars, and Supermassive Black Holes; the more massive a galaxy is, the more massive its central black hole is. Somehow, the black hole and the galaxy “know” enough about each other to match their growth rates.

Since Galaxies are observed over cosmological length and time scales, the description of their formation and evolution must involve cosmology. The study of properties of space and time on large scales. Modern cosmology is based upon the cosmological principle, the hypothesis that the universe is especially homogeneous and isotropic.

Types of galaxies are included Spiral galaxies, Elliptical galaxies, Irregular galaxies. This shape classification of galaxies was created by Edwin Hubble in 1926.

Spiral Galaxies: These are the most common type of galaxy in the universe. Of all known galaxies in the universe, 77% of them are classified as spiral galaxies.

Elliptical Galaxies: These are classified by their ovular shape and lack of central bulge.  

Irregular Galaxies: Each irregular galaxy doesn’t have a size or shape that is what we known as irregular. These don’t have any previously discussed components.

Milkyway Galaxy:

The Milkyway is the galaxy that contain our solar system, with the name describing the galaxy’s appearance from earth. A hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. From earth, the Mlikyway appears as a band because its disk shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s most astronomer thought that the Milkyway contained all the stars in the universe. In 1920, great debate between the astronomer Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milkyway is just one of many galaxies.

The Milkyway is a barred Spiral galaxy with an estimated visible diameter of 150-200,000 light years, an increase from traditional estimates of 100,000 light years. It is estimated to contain 100-400 billion stars and at least that number of planets. The solar system is located at a radius of about 27000 light years from the galactic center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.

It is the second largest galaxy in the local group (after the Andromeda galaxy), with its stellar disk approximately 170,000-200,000 light years in diameter and on average approximately 1000 light year thick. The Milkyway is approximately 890 billion to 1.54 trillion times the mass of the sun.

Star Formation in Galaxies:

Stars are heavily bodies, which shine like our sun. Many shines brightly, the others have a dim glow. Some are red while others are blue, stars are giant balls of gas made of hydrogen, bound together by their own force of gravity. The energy that makes them shine comes from a kind of power plant in their interior, where atomic nuclei of hydrogen atoms are fused together to form helium atoms. The stars don’t live forever and die at some point. Many simply get extinguished, while very heavy stars expand and explode. Their remains become either a neutron star or a blackhole.

How is a Star born?

The cradle of a star is a cloud of hydrogen and dust. There are numerous such clouds in the universe. By the action of external force –such as explosion of a star this cloud gets compressed and keeps pulling itself together due to increasing force of attraction among the particles. After a few hundreds of thousands of years, it begins to shine. A proto-star, a star in the early stages, is formed. This keeps pulling itself together while rotating, and becomes hotter and hotter, till its interior reaches a temperature of around 10-million-degree Celsius. In the core of the star, the fusion of hydrogen into helium releases an enormous amount of energy. Now, the star becomes a main sequence star. It shines approximately for 10 billion years, till it dies.

The life cycle of a star:

A proto- star arises from a cloud. The shining main sequence star explodes in a Supernova. Its mass collects together to form a neutron star or a blackhole.

Why do all stars not shine with the same intensity?

There are two reasons why all the stars in the night sky don’t shine equally brightly. Firstly, the stars are at different distances from the earth, secondly, the luminosity. Young stars are bright, hot and shine bluish- white, and older stars which have already given out a lot of their energy are red in colour. Our sun is middle aged (about 4.8billion years old) with a temperature of around 5778K on its surface, and shines with a bright yellowish-white color. Stars are like a window to the past. If a star is 10 light years away, we are observing 10 years back star.

How do stars die?

When the fusion of hydrogen into helium takes place in the core of the star, it continues to shine for about 10 billion years.

At some point of time, however, all the hydrogen gets consumed. Helium then melts to form carbon. What happens after this, depends on the mass of the star. Lighter stars like the sun expand to become a red giant, till the fusion stops, and then implode to become a white mass about the size of the earth. Very large stars, about 20 times heavier than our sun, expand to become a giant and finally explode. This is known as ‘Supernova’. The remains of supernova become either a neutron star or a blackhole.

Dark Matter:

Dark matter is a form of matter throughout to account for approximately 85% of the matter in the universe and about a quarter of its total mass energy density or about 2.241x10^-27 kg/m^3.

Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present that can be seen. For this reason, most experts think that dark matter is abundant in the universe and that it has had a strong influence on its structure and evolution. Dark matter is called dark because it doesn’t appear to interact with the electromagnetic radiation, and is therefore difficult to detect.

The hypothesis of dark matter has an elaborate history. In a talk given in 1884, lord Kelvin estimated the number of dark bodies in the milkyway from the observed velocity dispersion of stars orbiting around the center of the galaxy. Lord Kelvin thus concluded “many of our stars” perhaps a great majority of them, may be dark bodies.

Dark matter contributes 85% of total mass, while dark energy plus dark matter contributes 95% of total mass energy content. Because dark matter has not yet been observed directly, if it exists, it must barely interact with ordinary baryonic matter and radiation, except through gravity. Most dark matter is thought to be non-baryonic in nature. It may be composed of some as yet undiscovered subatomic particles. Dark matter is classified as “cold” “warm” or “hot” according to its velocity.

Black Hole:

Black hole is a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because matter has been squeezes into a tiny space. This can happen when a star is dying.

No light can get out of a black hole and all light is absorbed by it, so black holes cannot be seen but can be detected by its surroundings variations.

How big are black holes?

Black holes can be big or small scientists think the smallest black hole are as small as just one atom. These black holes are very tiny but have the mass of a large mountain.

Black holes are the concept which cannot be understood completely and in maximum cases the assumptions were made.

The largest black holes are called Supermassive. These blackholes have masses that are more than 1 million suns together. The supermassive blackhole at the center of the milky-way galaxy is called Sagittarius. It has a mass equal to about 4 million suns and would fit inside a large ball that would hold a few million earths.

How do black hole form?

Scientists think the smallest black holes formed when the universe began. Stellar black holes are made when the centers of a very big star falls in up to itself or collapses. When this happen, it causes a supernova is an exploding star, that blasts part of the star into space.

What happens if a person goes into a black hole?

If you jump into the black hole feet first, the gravitational force on your toes would be much stronger than that on your head and you will be elongated in a slightly different direction. you could literally end up looking like a Spaghetti.

Conclusion:

The study of galaxy formation is never ending and there is much more to know as we move on. However, linking observations to theory is significantly impeded by many uncertainties both observational and theoretical.

Currently most observational studies are based on mass limited galaxies, since stellar mass is relatively easy to measure well with many of its properties.

Finding a reliable way to trace real galaxies growth over a large mass range is one of the key challenges still facing this field.

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GREAT CONJUCTION OF SATURN AND JUPITER

Introduction:

A great conjunction is a conjunction of the planets Jupiter and Saturn, when the two planets appear closest together in the sky. Great conjunctions occur approximately every 20 years when Jupiter "overtakes" Saturn in its orbit. They are named "great" for being by far the rarest of the conjunctions between naked-eye planets (i.e. excluding Uranus and Neptune). 

Stitched photograph of the great conjunction of 2020 four hours before closest approach, with Jupiter 6–7 arcminutes below Saturn.

The spacing between the planets varies from conjunction to conjunction with most events being 0.5 to 1.3 degrees (30 to 78 arcminutes, or 1 to 2.5 times the width of a full moon). Very close conjunctions happen much less frequently (though the maximum of 1.3° is still close by inner planet standards): separations of less than 10 arcminutes have only happened four times since 1200, most recently in 2020.

History:

Great conjunctions attracted considerable attention in the past as omens. During the late Middle Ages and Renaissance, they were a topic broached by the pre-scientific and transitional astronomer-astrologers of the period up to the time of Tycho Brahe and Johannes Kepler, by scholastic thinkers such as Roger Bacon and Pierre d'Ailly, and they are mentioned in popular and literary works by authors such as Dante and Shakespeare. This interest is traced back in Europe to translations of Arabic texts especially Albumasar's book on conjunctions.

Despite mathematical errors and some disagreement among astrologers about when trigons began, belief in the significance of such events generated a stream of publications that grew steadily until the end of the 16th century. As the great conjunction of 1583 was last in the water trigon it was widely supposed to herald apocalyptic changes; a papal bull against divination was issued in 1586 but as nothing significant happened by the feared event of 1603, public interest rapidly died. By the start of the next trigon, modern scientific consensus had long-established astrology as pseudoscience, and planetary alignments were no longer perceived as omens.

Celestial mechanics: 

Diagram of longitude pattern from joannes kepler’s 1606 book De stella nova 

On average, great conjunction seasons occur once every 19.859 Julian years (each of which is 365.25 days). This number can be calculated by the synodic period formula in which J and S are the orbital periods of Jupiter (4332.59 days) and Saturn (10759.22 days), respectively. (In practice, Earth's orbit size can cause great conjunctions to reoccur up to some months away from the average time or the time they happen on the Sun). Since the equivalent periods of other naked-eye planet pairs are all under 27 months, this makes great conjunctions the rarest.

Occasionally there is more than one great conjunction in a season when they occur close enough to opposition: this is called a triple conjunction (which is not exclusive to great conjunctions). A triple conjunction is a conjunction of Jupiter and Saturn at or near their opposition to the Sun. In this scenario, Jupiter and Saturn will occupy the same right ascension on three occasions or same ecliptic longitude on three occasions depending on which definition of "conjunction" one uses (this is due to apparent retrograde motion and happens within months). The most recent triple conjunction occurred in 1980–81 while the next will be in 2238–39.

Diagram showing the movements of Jupiter and Saturn during the 1980–81 triple conjunction.

The most recent great conjunction occurred on 21 December 2020, and the next will occur on 4 November 2040. During the 2020 great conjunction, the two planets were separated in the sky by 6 arcminutes at their closest point, which was the closest distance between the two planets since 1623. The closeness is the result of the conjunction occurring in the vicinity of one of the two longitudes where the two orbits appear to intersect when viewed from the Sun (which has a point of view similar to Earth).

Because 19.859 years is equal to 1.674 Jupiter orbits and 0.674 Saturn orbits, three of these periods come close to a whole number of revolutions. This is why the longitude cycle, as shown in the diagram, has a triangular pattern. The three points of the triangle revolve in the same direction as the planets at the rate of approximately one-sixth of a revolution per four centuries, thus creating especially close conjunctions on an approximately four-century cycle. Currently the longitudes of close great conjunctions are about 307.4 and 127.4 degrees in the constellations Capricornus and Cancer respectively. The position of Earth in its orbit, however, can make the planets appear up to about 10 degrees ahead of or behind their heliocentric longitude.

Saturn's orbit plane is inclined 2.485 degrees relative to Earth's, and Jupiter's is inclined 1.303 degrees. The ascending nodes of both planets are similar (100.6 degrees for Jupiter and 113.7 degrees for Saturn), meaning if Saturn is above or below Earth's orbital plane Jupiter usually is too. Because these nodes align so well it would be expected that no closest approach will ever be much worse than the difference between the two inclinations. Indeed, between year 1 and 3000, the maximum conjunction distances were 1.3 degrees in 1306 and 1940. Conjunctions in both years occurred when the planets were tilted most out of the plane: longitude 206 degrees (therefore above the plane) in 1306, and longitude 39 degrees (therefore below the plane) in 1940. 

Notable great conjunctions (1200 to 2400):

7 BC 

When studying the great conjunction of 1603, Johannes Kepler thought that the Star of Bethlehem might have been the occurrence of a great conjunction. He calculated that a triple conjunction of Jupiter and Saturn occurred in 7 BC (−6 using astronomical year numbering).

In the year 1563,

The astronomers from the Cracow Academy (Jan Muscenius, Stanisław Jakobejusz, Nicolaus Schadeck, Petrus Probosczowicze, and others) observed the great conjunction of 1563 to compare Alfonsine tables (based on a geocentric model) with the Prutenic Tables (based on Copernican heliocentrism). In the Prutenic Tables the astronomers found Jupiter and Saturn so close to each other that Jupiter covered Saturn (actual angular separation was 6.8 minutes on 25 August 1563). The Alfonsine tables suggested that the conjunction should be observed on another day but on the day indicated by the Alfonsine tables the angular separation was a full 141 minutes. The Cracow professors suggested following the more accurate Copernican predictions and between 1578 and 1580 Copernican heliocentrism was lectured on three times by Valentin Fontani. 

In the year 2020, 

Separation of Jupiter and Saturn around the time of the 2020 great conjunction 

The great conjunction of 2020 was the closest since 1623 and eighth closest of the first three millennia AD, with a minimum separation between the two planets of 6.1 arcminutes. This great conjunction was also the most easily visible close conjunction since 1226 (as the previous close conjunctions in 1563 and 1623 were closer to the Sun and therefore more difficult to see). It occurred seven weeks after the heliocentric conjunction, when Jupiter and Saturn shared the same heliocentric longitude.

The closest separation occurred on 21st December at 18:20 UTC, when Jupiter was 0.1° south of Saturn and 30° east of the Sun. This meant both planets appeared together in the field of view of most small- and medium-sized telescopes (though they were distinguishable from each other without optical aid). During the closest approach, both planets appeared to be a binary object to the naked eye. From mid-northern latitudes, the planets were visible one hour after sunset at less than 15° in altitude above the southwestern horizon in the constellation of Capricornus.

The conjunction attracted considerable media attention, with news sources calling it the "Christmas Star" due to the proximity of the date of the conjunction to Christmas, and for a great conjunction being one of the hypothesized explanations for the biblical Star of Bethlehem. 

Sky watching programme on great conjugation of Saturn and Jupiter at St.Philomena College, Puttur

Reference:-

1. Wikipedia 

2. Newspaper
3. Journals

SUBMITTED BY:- 

Anagha R 

Ananya Rai S
Bhavya DSouza
Deeksha M
Dileep Delmond D Souza
Kadhija Tabhseera

1st M.Sc. {1st Semester}
SUBMITTED ON:- 11-01-2021