What are the Astronomers, who helped enhance our understanding of the cosmos?

We have always been looking up, peering into the sky, trying to find answers to the many questions about the universe. Many astronomers have tried to unravel the mysteries of the universe. From believing that Earth was flat and the planets revolved around it, we have come a long way. Let's take a look at some of history's greatest astronomers who helped enhance our understanding of the Cosmos.

From believing that the Earth was flat and the planets revolved around it, we have come a long way.Some 2000 years ago, when it was widely believed that the world was flat, Greek mathematician and astronomer Eratosthenes (276 BC-194 BC) calculated the Earth's circumference. In those days, the very act of coming up with scientific thoughts which were at odds with the ones in existence was not encouraged. The theory that the Earth revolved around the Sun was itself considered heretical by the religious and after a trial, Italian astronomer Galileo Galilei was kept under house arrest until his death. Polish astronomer Nicolaus Copernicus didn't publish his magnum opus "De revolutions orbium coelestium" (On the Revolutions of the Heavenly Spheres) until he was on his deathbed. Let's take a look at some of history's greatest astronomers who threw new light on the cosmos.

CLAUDIUS PTOLEMY (AD 100-AD 170)

 Astronomer and mathematician Claudius Ptolemy authored several scientific teas and is noted for his Ptolemaic system. It was a geocentric (Earth-centred) model of the universe, where the sun, stars, and other planets revolved around Earth. This model was used for a long period, for over 1200 years, until the heliocentric view of the solar system was established. Although his model of the universe was wrong, his work and the scientific texts he authored helped astronomers make predictions of planetary positions and solar and lunar eclipses. "The Almagest, a comprehensive treatise on the movements of the stars and planets, was published in the 2nd Century. It is divided into 13 books. This manual served as the basic guide for Islamic and European astronomers. He also catalogued 48 constellations. 

NICOLAUS COPERNICUS (1473-1543)

 Nicolaus Copernicus changed the way scientists viewed the solar system. Back in the 16th Century, he came up with a model of the solar system where the Earth revolved around the Sun: it was the revolutionary heliocentric model. He removed Earth from the centre of the universe and replaced it with the Sun! He also didn't believe in the Ptolemaic model of the planets travelling in circular orbits around the Earth. He also explained the retrograde motion of the planets (retrograde motion is when planets appear to move in the opposite direction of the stars). When the Polish astronomer was 70, he published his book "De Revolutions Orbium Coelestium" ("On the Revolutions of the Heavenly Spheres"), on his deathbed. It took over a century for his idea to gain credence.

GALILEO GALILEI (1564-1642)

Optical astronomy began with Galileo Galilei. Born in Italy, Galilei is credited with creating the optical telescope. In fact, what he did was improve upon the existing models. He came up with his first telescope in 1609, modelling it after the telescopes produced in other parts of Europe. But here is the catch. Those telescopes could magnify objects only three times. Galileo came up with a telescope that could magnify objects 20 times. He then pointed it towards the sky, coming up with the greatest discoveries ever. He discovered the four primary moons of Jupiter which are referred to as the Galilean moons. He also discovered the rings of Saturn. Even though the theory of Earth circling the Sun had been around since Copernicus’ time, when Galileo defended it, he was kept under house arrest till the end of his lifetime.

JOHANNES KEPLER (1571-1630)

Danish astronomer Johannes Kepler modified the Copernican view of the solar system and changed it radically. He deduced that the planets travelled in elliptical orbits, one of the most revolutionary ideas at the time, replacing Copernicus view that they travelled in circular objects. He came up with three revolutionary laws involving the motions of planets these three laws make him a towering figure in astronomy. Kepler also observed a supernova in 1604. It is now called Kepler's Nova.

EDMOND HALLEY (1656-1742)

"Halley's comet is perhaps a term you would have heard quite often. English astronomer Edmond Halley never saw the comet named after him. Officially called 1P/Halley, Halley's  comet  is a periodic comet that passes by the Earth once every 76 years (roughly). This famed comet will return in 2061. It was Halley's mathematical prediction of the comet's return that made him a towering figure among the list of astronomers. He said that the comet that appeared in 1456, 1531, 1607, and 1682 were all the same and that it would return in 1758. Halley was never around to witness this, but the world saw the comet and its return. The comet was later named in his honour. One of the earliest catalogues of the southern sky was also produced by Halley. In 1676, he sailed to the island St. Helena, South Atlantic Ocean. There he spent a year measuring the position of stars and came up with the first catalogue of the southern sky! Seen here is a painting of the astronomer. 

WILLIAM HERSCHEL (1750-1848)

Musician-tumed astronomer William Herschel started exploring the skies with his sister Caroline quite late in his career but eventually, he compiled a catalogue of 2.500 celestial objects The German astronomer discoverest the planet Uranus and several moons of other planets it was during his mid 30s that he startet looking up and exploring the cosmos In 1759. Herschel left Germany and moved to England where he started teaching music When Herschels interest in astronomy grew, rented a telescope. He then went ahead and built himself a large telescope to watch the celestial bodies. His sister Caroline assisted him until Herschel's death and also became the first woman to discover a comet. She eventually discovered eight of them. When Herschel found a small object in the night sky, he explored further and found out that it was a planet. The Uranus was thus discovered. He was knighted by the monarch after the discovery and was appointed the court astronomer. Following this he gave up his music career and devoted himself to the skies. He found the moons of Uranus and Saturn Craters on the moon. Mars and Mimas (Saturn's moon) are named after the astronomer.

ANNIE JUMP CANNON (1863-1941)

Known as the "census taker of the sky, American astronomer Annie Jump Cannon made stellar contributions to the field of astronomy. She classified around 3,50,000  stars manually. At a time when gender representation in astronomy was  skewed. Cannon with her impeccable contributions inspired many women to pursue astronomy. During that time, stars were classified alphabetically, from A to Q. based on their temperatures. She built a new classification system with ten categories and forever changed the way scientists classified stars by developing the Harvard system which is in use even today.

CARL SAGAN (1934-1996)

American astronomer Carl Sagan was not just a science poster boy but he was one of the most influential voices in the scientific  realm  who  made the cosmos a subject of interest for the masses. Sagan played a huge role in in the American space program. He popularised astronomy and through his talks and books motivated many to become sky watchers. He also founded the Planetary Society, a non-profit that is focussed on advancing space science and exploration. He was a professor of astronomy and space sciences and director of the Laboratory for Planetary Studies at Cornell University. His contributions include explaining the high temperatures of Venus and the seasonal changes on Mars. His book "Cosmos" is a bestseller that was also turned into a television show (hosted by Sagan) which was watched by a billion people in 60 countries. He also wrote a science fiction novel "Contact" which was adapted to the screen.

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What is Gaganyaan Mission?

Four Indian pilots, who were selected to become astronauts to crew Gaganyaan, the country's first manned space mission, have returned after completing their one-year training course in Russia's Zvyozdny Gorodok city near Moscow. The contract for the training of Indian officers was signed between the Indian Space Research Organisation (ISRO) and Russian launch service provider Glavcosmos in June 2019. The four pilots of the Indian Air Force (IAF) include a Group Captain and three Wing Commanders, according to the IAF sources. The training began on February 10, 2020, but was temporarily interrupted due to the COVID-19 pandemic.

The ISRO said the astronauts will now receive module-specific training in India. They will be trained in crew and service module designed by the ISRO, learn to operate it, work around it and do simulations.

Meanwhile, the Indian space agency signed an agreement with the French space agency CNES to help prepare for the Gaganyaan mission and to serve as its single European contact in this domain. How will France help India in the mission? What is Gaganyaan all about?

What is Gaganyaan Mission all about?

Gaganyaan is a 10.000-crore manned space mission, which will launch three Indian astronauts (the fourth astronaut will be a backup) to circle Earth at a distance of about 300-400 km from the surface for up to seven days. If successful, India will become the fourth nation to send a person into space, after Russia, the U.S. and China,

The crew will be launched into space using an indigenous Geosynchronous Satellite Launch Vehicle Mark III (GSLV Mk-lll rocket), from the refurbished launchpad at Sriharikota. The ISRO will carry out two unmanned missions before the manned space flight.

The crew was expected to commence its journey in 2022, following the formal announcement of the Gaganyaan project in August 2018. But the ISRO stated in late 2020 that the Gaganyaan project will be "slightly delayed due to COVID-19. In a written statement to the Lok Sabha, Jitendra Singh, Union Minister of State for the Department of Space said. "First unmanned mission is planned in December 2021. Second unmanned flight is planned in 2022-23, followed by human space flight demonstration."

Who is leading the project?

V.R. Lalithambika, a specialist in advanced launcher technologies, is the Director of the Human Spaceflight Programme. She has worked on rocket technologies such as the Polar Satellite Launch Vehicle (PSLV) and the GSLV.

Why GSLV-MK III?

A launch vehicle that can carry heavy payloads into space is important for a human spaceflight project. ISRO'S GSLV Mk-ll, the country's heaviest rocket, is considered to be ideal as the 640-tonne and 43- metre-tall rocket can launch 10 tonnes of payload into low-Earth orbit, an altitude of 2.000 km or less above the planet. The crew module is likely to weigh in excess of 5 to 6 tonnes.

Whereas ISRO's main launch vehicle, the PSLV, which carried the Chandrayaan and Mangalyaan missions, weighs about 320 tonnes and can carry payloads up to two tonnes and to orbits of 600 km altitude from the Earth's surface, and hence is not suitable to send a crew into space.

How did the project take shape?

2004: The ISRO Policy Planning Committee made recommendations for a manned space mission 2006: Preliminary studies of Gaganyaan started under the generic name Orbital Vehicle.

2008: An initial design of a fully autonomous vehicle to carry two astronauts was finalised by March 2008 and was submitted to the Government of India for funding.

2009: A committee was formed to analyse the feasibility of the programme. The committee expressed support.

February 2009: The funding for the Indian Human Spaceflight Programme was sanctioned.

December 18, 2014: Successful testing of experimental flight of GSLV Mk-lll was carried out. The launch also involved the successful testing of an experimental crew module. Called the Crew module Atmospheric Re-entry Experiment (CARE), the spacecraft reentered the atmosphere at about 80 km altitude and landed in the sea near the Andaman and Nicobar Islands, from where it was recovered. June 5, 2017: First flight of GSLV Mk-lll was carried out. GSLV Mk-ill placed the country's heaviest satellite till date. GSAT19, into a precise orbit. With it India became a nation having its own indigenous cryogenic engine technology.

July 5, 2018: First successful flight of the crew escape system was carried out. The crew escape system is an emergency measure designed to quickly pull the crew module along with the astronauts to a safe distance from the launch vehicle in the event of a launch abort. A simulated crew module weighing about 3.5 tonnes was launched from Sriharikota. It reached 2.7 km into space before unfurling its parachutes and floating back to the Earth's surface. August 15, 2018: Prime Minister Narendra Modi promised manned mission before 2022.

May, 2020: The ISRO invited startups and private players to develop R&D solutions for food and medicine for the astronauts, support systems such as space suits, and anti-radiation and thermal protection technologies for spacecraft while returning to Earth.

What does the recent Indo France agreement on the mission mean?

According to news reports, the CNES will train India's flight physicians and CAPCOM mission (the Capsule Communicator, or CAPCOM) control teams in France. The agreement also provides for the CNES to support implementation of a scientific experiment plan on validation missions, exchange information on food packaging and nutrition, and the use of French equipment, consumables and medical instruments by Indian astronauts.

French equipment developed by CNES, tested and still operating aboard the International Space Station (ISS), will thus be made available to Indian crew members. The CNES will also be supplying fireproof carry bags made in France to shield equipment from shock and radiation.

What is Vyommitra?

Vyommitra is a robot, half-humanoid to be exact. It has been developed by the ISRO and it will accompany Indian astronauts on Gaganyaan. It will also be part of the uncrewed experimental Gaganyaan missions prior to the crewed spaceflight mission.

But what's the purpose? In the early years of space flight, there were concerns whether humans could mice, survive in space. So animals such as fruit flies, monkeys and cats were sent before the first human ventured into space to test the survivability of spaceflight.

But India will not fly animals into space. Instead, it will launch the robot. On the uncrewed mission, the robot will help the Indian space agency to understand what weightlessness and radiation can do to the human body during long durations in space.

While onboard the crewed mission. Vyommitra can detect and give out warnings if environmental changes within the cabin get uncomfortable to astronauts and change the air condition. It is programmed to speak Hindi and English and perform multiple tasks. It can mimic human activity, recognise other humans, and respond to their queries.

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How did Earth get its magnetic field?

Earth’s magnetic field behaves like a giant bar magnet with north and south poles. Many mechanisms have been postulated to explain how the magnetic field is generated, but the only one that is widely accepted is analogues to a dynamo. That is, Earth’s magnetic field is caused by a dynamo effect.

The mechanism is similar to that of the working of a dynamo start spinning when the bicycle is pedaled, creating an electric current. The electricity, thus created, keeps the light on. Magnetic fields occur whenever electric charge is in motion. If there is a rotating electric current, it will create a magnetic field.

The Earth’s magnetic field has its source in the flow of molten iron in its outer core. Electric current is generated due to the motion of convection currents of molten iron. The rotation of Earth on its axis causes these electric currents to form a magnetic field which extends around the planet.

 

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What’s beyond the Milky Way?



All the stars you can see at night belong to our galaxy, the Milky Way. To get a grasp of the size of the Milky Way, let's consider the time for light to travel from one place to another. It takes about one second for light to reach us from the surface of the Moon, eight minutes from the Sun, and four years from the nearest other star. But from the edges of the Milky Way, light takes tens of thousands of years! And despite its vastness, the Milky Way is just one galaxy amongst billions of other galaxies scattered in the immensity of the universe.



Our closest neighbours are small galaxies orbiting the Milky Way. Beyond them, the Andromeda Galaxy is bigger than the Milky Way. The Milky Way will eventually collide with it. For the moment though, its light takes more than two million years to reach us. Even farther away lies the Virgo duster, which comprises more than a thousand galaxies. But this is still the neighbourhood of our Milky Way. The farthest galaxy ever observed is so far it takes light 13 billion years to reach us. Wherever telescopes look, they spot thousands and thousands of galaxies!



 



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How do astronauts write in space?



Legend has it that during the height of the space race in the 1960s, NASA scientists figured that pens could not function in space. So, they spent millions of dollars developing a pen that could write in space, while their Soviet counterparts used the humble pencil.



This story has been floating around the Internet for way too long. However, it is just a myth.



The truth



According to NASA historians, NASA astronauts also used pencils. In 1965, NASA ordered 34 mechanical pencils from Houston's Tycam Engineering Manufacturing, Inc. at the rate of $ 128.89 per pencil. When the public got to know about these rates, there was an outcry, and NASA had to find something much cheaper for its astronauts to use.



The pencil loses out



The pencil wasn't an ideal choice for writing in space because its tip could flake and break off, drifting in microgravity with the potential to harm an astronaut or an equipment. Apart from this, pencils are flammable, and NASA wanted to avoid anything flammable aboard a spacecraft.



And the pen?



Regular pens that work on Earth did not work in space because they rely on gravity for the flow of ink to the nib. This was understood quite early by scientists and hence astronauts used pencils. But with both the pencil and the pen creating issues, what did NASA finally resort to?



The saviour



Around the time NASA was embroiled in the mechanical pencils controversy, Paul C. Fisher of the Fisher Pen Co. designed a ballpoint pen that could work in space. His company invested one million dollars to fund, design, and patent the pen on its own.



Fisher's pen operated seamlessly, not just in space, but also in a weightless environment, underwater, in other liquids, and in temperatures ranging from -50 F to +400 F.



The company offered the pen to NASA, but the space agency was hesitant to buy it due to the mechanical pencil controversy.



However, a few years later, after rigorous testing, NASA agreed to equip its astronauts with the space pen. The space agency bought 400 pens from Fisher. And a year later, the Russians also ordered 100 pens and 1,000 ink cartridges to use on their Soyuz space missions. Both NASA and the Soviet space agency received a 40 % discount on bulk purchase of the pens, paying about $ 2.39 per pen.



Over the years, Fisher's company has created different space pens, which are still used by NASA and the Soviet space agency.



If you would like to get your hands on one of these space pens, it would cost you approximately $ 50.



 



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Why do astronauts become weightless in space?



The idea of floating about completely weightless sounds great fun, but try to imagine what it must be like to lose normal control of your body. Astronauts have to learn to live in these conditions, sometimes for months on end, because when they are in space their bodies become apparently weightless. Once a spacecraft is in orbit around the earth, it remains held in position by the earth's gravity. The astronauts inside are moved by the same force, and since they and the spacecraft are moving in the same way, they are not drawn down to the floor but float about.



There is one curious side-effect of weightlessness which is encouraging to anyone who would like to be a little taller. Because their bodies are not pulled down to earth by the force of its gravity, astronauts find that they stretch a little in space. The effect does not last for long once they return to earth. Gravity soon pulls them back to their original height.



 



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Why is the moon covered with craters?



Pictures of the moon’s surface show that it is pockmarked with round walled shapes known as craters. What caused them is a bit of a mystery. Men have landed on the moon several times. A lot of satellites have been sent to look at it. Yet scientists still cannot say for certain what caused the craters. The moon does not have an atmosphere like the earths. This makes it easier for meteorites to smash into its surface. Meteorites heading towards earth often break up as they pass through the atmosphere. So meteorites probably caused a good many of the moon’s craters.



A lot of the craters are huge. Some measure over 150 kilometres across. Others are so tiny they cannot be seen from earth. So another theory is that some craters may have been formed by volcanic activity bubbling up from inside the moon.



Most likely both meteorites and internal eruptions were responsible. But we still do not know for certain.



 



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How do space scientists make sure that their rockets land on the moon?



It may sound silly, but imagine what would happen if a rocket sent up to the moon missed its target. The moon may be pretty big. But so in space. Missing something even as big as that could easily happen, without careful control of the spacecraft. That’s why each moon shot takes months of planning and complicated calculations.



The rocket must be programmed so that soon after take-off it reaches almost 42,000 kilometres per hour. This is the speed necessary for it to break free of the earth’s gravity. After that, its speed has to be carefully controlled so that when it reaches the moon it will be travelling at about 1250 kilometres per hour.



Of course, while a rocket is flying to the moon, the moon is on the move as well. It is whizzing round the earth at an average speed of 3836 kilometres per hour. Just to complicate things further, it does not stick to a regular path. The distance between the earth and the moon can vary by as much as 52,800 kilometres! The flight controllers have to work out where the moon is going to be all through the flight, to be certain that the rocket reaches the right place at the right time. Then there is the moon’s gravity to be taken into consideration. The closer a rocket gets to the moon, the more it is affected by this gravitational pull. So for the last 3000 kilometres the scientists have to watch the rocket’s speed very closely as it becomes more and more affected by the moon’s gravity.



You can see that controlling the speed and navigation of a spacecraft is anything but easy. The speed has only got to be a couple of kilometres an hour either side of the right speed to miss the moon completely. And one degree off course could throw the rocket’s timing out by as much as seven hours.



 



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What would happen to an astronaut if he/she were to be lost in space without a spacesuit?



We know that astronauts and cosmonauts travel to space in spacecraft and require a spacesuit when they venture out of the spacecraft. An astronaut's spacesuit creates a pressurised, oxygenated atmosphere to help the astronaut breathe. It also protects the astronaut from ultraviolet rays and extreme temperatures in space. But what would happen to an astronaut if she were to be lost in space without a spacesuit?



Time in hand - not much



The astronaut will not die immediately on being exposed in space. She will have close to 15 seconds before she loses consciousness and another two to three minutes before death comes knocking. Before the two minute mark if she is pulled in by someone from the spacecraft, she does have chances of survival but her body would have gone through quite a bit.



The top cause



Not zero pressure - It is assumed that one would explode in space without a spacesuit due to zero pressure. However, this is not true. The skin is gas-tight and is strong enough to withstand any kind of pressure. Not inflation - While the body won't explode, it can still inflate due to nitrogen bubbles that would have dissolved in the bloodstream near the surface of the skin, and collected itself into little bubbles. These little bubbles will start expanding, puffing up the body, starting at the hands and feet and moving in. This is called ebullism. Ebullism can cause significant tissue damage, but it won't be the cause of death.



Not the cold - Space is really, really cold. But it will still not lead to hypothermia instantly. This is because, in a vacuum, the only way to lose heat is by radiation or by evaporation of fluid. And the human body loses heat by radiation very slowly as it is a relatively cool object. The body will eventually freeze if it is in space for too long, but there is something else that would lead to death before any of the points mentioned above. That is asphyxiation.



Yes, asphyxiation - There is no air in space, and our blood holds enough oxygen to last about 15 seconds. Post this, the brain shuts down and the astronaut will lose consciousness. If she is not pulled back in within a minute or two, all the other organs in the body will eventually shut down due to the lack of oxygen, leading to death.



Interesting fact:



Holding the breath while being exposed to the vacuum in space will cause the air in the lungs to rupture the lung tissue as it expands into the chest cavity, forcing air bubbles into the bloodstream. This can prove to be fatal even if the astronaut is rescued.



So, it important for an astronaut to not hold her breath is space.



 



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Why Jupiter is often referred to as a failed star?



Jupiter is known to us as the largest planet in our solar system and a gas giant. But did you know Jupiter is often referred to as a failed star



Not quite the mass



Jupiter is dubbed by many as a failed star because it is mostly made up of hydrogen and helium, like the Sun, but it is does not have enough mass to reach the internal pressure and temperature necessary to fuse hydrogen into helium and kickstart thermonuclear fusion. Its mass is 2.5 times that of all the other planets in the solar system combined, but it is still not enough to make Jupiter a star. The planet has only 0.1 % of the mass of the Sun.



Jupiter never had a chance



Many scientists argue that it is unfair to call Jupiter a failed star because it never had the chance to become one. Stars and planets form in different ways. A star is formed when a cloud of interstellar gas and dust collapses unto itself. Because of rotation, these clouds form flattened accretion discs that surround the central growing star. As the mass of the star grows, collecting material from the disc, the core of the star starts to squeeze and become tighter, thereby causing it to become hotter. Eventually, the core becomes so compressed and hot that it ignites, and thermonuclear fusion kicks off. At this point, the star stops collecting material from the disc and all the leftover material is free to form planets.



When it comes to the formation of Jupiter, scientists believe it happened in two steps. Initially, tiny chunks of icy rock and dust present in the accretion disc started colliding and forming a planetary embryo. Once this embryo was large enough (about 10 times more massive than Earth), its self-gravity became strong enough to pull in gas and dust directly from the disc During this step, Jupiter gained most of its mass, but it wasn't enough to make it a star. The Sun probably took away most of the mass from the disc leaving almost nothing for Jupiter to become a star.



 



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Why do Venus and Uranus spin backwards?



 



We know that the planets in our solar system orbit the Sun and rotate around their own axis in a counterclockwise (west to east) direction. But while all the planets orbit the Sun in this direction, not all of them rotate the same way around their own axis. Venus and Uranus rotate clockwise (east to west), also called retrograde rotation. During the formation of our solar system these two planets spun the same way as others, but there is no definite answer as to when and why they started spinning backwards. However, there are several theories.



The backward-spinning Venus



There are two main theories that try to explain Venus backward / retrograde rotation. The first theory suggests that at some point in time, post the formation of the solar system, Venus flipped its axis 180 degrees. This means, Venus continues to spin in the same direction as it always has, except it is now upside down. So, when looked at from other planets, Venus looks like it is spinning in the opposite direction.



Scientists believe Venus axis might have flipped due to the Sun's strong gravitational pull on the planet's dense atmosphere, which could have caused strong atmospheric tides. These tides, combined with the friction between Venus' mantle and core might have caused the flip.



The second theory states that Venus might not have flipped at all. Scientists propose that the planet's rotation slowed to a standstill and reversed direction. Scientists suggest this theory taking into account the factors mentioned in the first theory coupled with the tidal effects from other planets. They believe this might have caused Venus to eventually spin in a more stable retrograde state.



The side-spinning Uranus



Uranus, like Venus, rotates in the clockwise direction but its axis is tilted at 97.77 degrees, making the planet appear as though it is spinning sideways and orbiting the Sun like a rolling ball. The most popular theory suggested by scientists for Uranus tilt is the collision of the planet with an Earth size object. A more recent theory suggests that Uranus wasn't hit once by a giant object, but collided multiple times with objects of a smaller size.



A collision-free theory suggests that during the initial days of planetary migration, Uranus had a large Moon whose gravitational pull caused the planet to fall on its side. During the same planetary migration, this moon is believed to have been knocked out of orbit by another planet.



 



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How can you describe the Trojan asteroids?



Trojan asteroids are asteroids that share an orbit with a planet and are located at the leading (L4) and trailing (L5) Lagrangian points of the planet’s orbit. Lagrangian points or Lagrange points are locations in space where the combined gravitational forces of two large bodies, such as the Earth and Sun, equals the centripetal force required for a small object to move with them. Thus, if a spacecraft is to be parked at this point, the fuel consumption required to keep it in place can be reduced. There are five Lagrangian points in total, of which three are unstable (L1, L2, L3) and two are stable (L4 and L5). L4 leads the orbit of the planet and L5 follows.



How were they discovered?



On February 22, 1906, German astrophotographer Max Wolf discovered an asteroid with an unusual orbit. This asteroid remained ahead of Jupiter as the planet moved. To him, it seemed as though the asteroid was trapped in Jupiter’s orbit around the Sun. Meanwhile, German astronomer Adolf Berberich observed that the asteroid was nearly 60 degrees in front of Jupiter. This reminded Swedish astronomer Carl Charlier of a behaviour predicted nearly a century earlier by Italian-French mathematician Joseph-Louis Lagrange. Lagrange had stated that if a small space body such as an asteroid were to be placed at one of two stable points in a planet’s orbit around the Sun, the asteroid would remain stationary from the planet’s perspective.



This is when Charlier realised that the asteroid discovered by Wolf was caught in Jupiter’s L4 Lagrange point. Until this discovery, Lagrange’s prediction was only a mathematical exercise, but now there was photographic proof that Lagrange was right.



How did they get their name?



About eight months after Wolf’s discovery, one of his students, August Kopff discovered an asteroid in Jupiter’s L5. And then again a few months later, he discovered another asteroid caught in Jupiter’s L4. Once these discoveries were made, astronomers started wondering what to call these asteroids. While most asteroids at this point in time were named after women from Roman and Greek mythology, Austrian astronomer Johann Palisa suggested the names Achilles, Patroclus, and Hektor after characters from The Iliad (a Greek poem set during the Trojan War), due to the strange orbit of these asteroids.



 



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Why do stars have different colours?



Stars all look the same colour, don’t they? That’s true if you see them with the naked eye. Through a telescope the picture changes. Once you look at stars when they are magnified, you see that they all have different colours.



Surface temperature controls the colour of a star. Our most familiar one is the sun. That has a surface temperature of around 5000  and is yellow-white in colour. There are plenty of stars in the universe far hotter than the sun. The hottest are twice as hot on the surface, and these are blue. Surprisingly, red stars are the coolest ones. The surface temperature on these is about 3000 . Knowing this, scientists are able to estimate the surface temperature of stars by carefully measuring their colours.



 



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Do you know how satellites are used?



Today there are many artificial satellites that revolve round the Earth. Why is all the time, money and effort required to launch them considered worthwhile? The answer is that the satellite performs many useful scientific tasks as it journeys through space.



Artificial satellites can act as spies that seek out military installations and equipment on the Earth below. Another function is communications between distant points of the globe.



They can study the solar radiation and environment of space and this knowledge helps us to understand the forces at work on our own planet and the causes of natural phenomena which effect our living conditions.



Meteorological satellites also exist which record details of weather conditions throughout the world and help in weather forecasting.



 



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How the solar system moves in space?



During the 1700s after a great deal of hard work astronomers were able to calculate the speed and direction of many stars. By 1805 the astronomer Herschel proved that the Sun itself was subject to the same laws of movement. We now know that the Sun with its whole accompaniment of planets travels through space at the terrifying speed of about 270 kilometres a second together with the whole galaxy in which the solar system lies. The Sun also travels along a path of its own which is directed at a point in the heavens near the star Vega.



Herschel had studied the distant nebulae which astronomers before him believed to be millions of stars. Even the Milky Way was a nebula, but it was much brighter than the others and therefore must be nearer.



Herschel then thought that the Sun, like hundreds of other stars visible from the Earth, was part of huge nebula, separate from all the others and forming a universe of its own:  the galaxy.



During the 1870s the first powerful telescopes found other nebulae outside the galaxy and this proved that Herschel was right. New searches were made in our own century with the installation of the Mount Wilson telescopes in 1905 and the one at Mount Palomar in 1948.Today we can even begin to draw a map of the galaxy. It appears to be shaped like a 100,000 light years (one light year is equal to 10 million kilometres) and contains about 100,000 million stars.



 



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