Halley’s Comet (from a different perspective) You are here: Home / Picture of the Day / Halley’s Comet (from a different perspective) Halley’s Comet (from a different perspective) January 5, 2010 Click here for a larger view Photo courtesy of the European Space Agency . Perhaps no other heavenly body commands more attention when it comes within view of our planet than Halley’s Comet . There are probably few among us indeed who didn’t catch at least a brief glimpse of the storied comet when it made its last appearance just a few years ago. Comets have long been viewed through telescopes and photographed, but the mysterious objects’ nuclei have always remained veiled by the bright glow that surrounds them. But that changed in 1986 when a European spacecraft named Giotto encountered Halley at close enough range to create an image that clearly shows the comet’s potato shaped nucleus. Thanks to the efforts of Giotto, those who are lucky enough to still be around when Halley again comes calling in the year 2061 will be able to look at this most famous of all comets in an entirely different light.

Once a myth, now an object of study / Rosetta / Space Science / Our Activities / ESA Once a myth, now an object of study Comet 67P/Churyumov-Gerasimenko 23 February 2004 ESA INFO 05-2004. On 26 February, Rosetta will be setting off on its long journey through our solar system to meet up with Comet Churyumov-Gerasimenko. It will take the European Space Agency (ESA) space probe ten years to reach its destination. The comet, which moves in an elliptical orbit around the Sun, will at rendezvous be some 675 million kilometres from the Sun, near the point in its orbit farthest from the Sun. The meeting point was not chosen at random: at this point the comet is still barely active, it is still in fact a frozen lump of ice and interplanetary dust, in all probability the matter from which our solar system emerged four and a half billion years ago. Rosetta’s job is to find out more about these strange bodies that travel through our solar system. As it moves on, the comet will begin to change.

As it approaches the Sun, it will - like all comets - become active: in the warmth of the Sun’s rays, the ices evaporate, tearing small dust particles from the surface. This produces the comet head (the coma) and tail. Only these two features are visible from Earth. The comet nucleus itself is far too tiny - Comet 67/PChuryumov-Gerasimenko measures about 4 kilometres across - to be viewed from Earth. Dr Uwe Keller, of the Max Planck Institute for Aeronomy in Kaltenburg-Lindau, Germany, is the scientist responsible for the Osiris camera carried by Rosetta and he explains, “Formation of the coma and tail during solar flyby skims several metres of matter off the comet’s surface. In the case of a small comet like Churyumov-Gerasimenko, the shrinkage is a good 1% each time round.” As it flies past the Sun every 6.6 years it can look forward to a short future, especially on a cosmic timescale. Comets - a mystical view Visible cometary phenomena have fascinated human beings from time immemorial – and frightened them too. Even today mystical explanations prevail among some of the Earth’s peoples.

The Andaman islanders, a primitive people living in the Gulf of Bengal, see comets as burning torches hurled into the air by forest spirits – the more easily to detect humans foolish enough to stay out at night. For some Australian aborigines, comets are flaming sticks ridden by mighty shamans. Efforts to provide a scientific explanation of the ‘cometa aster’ (‘hairy star’) phenomenon stretch back to ancient times. A widely held view was that comets were in some way connected with processes at work in the atmosphere. In Meteorologica, Aristotle (384-322 BC) described how inflammable gases escape from clefts in rocks, collect in the upper layers of the sub-lunar world (‘world under the Moon’) and ignite. Rapid release of such gases produced a shooting star; when let out slowly, they gave rise to a comet. That was Aristotle’s best shot - and he was well aware of his limited insight into the question. As he himself acknowledged: “As we have no demonstrable basis for assertions about comets, I have to settle for an interpretation that does not conflict with established truths.” Admittedly such truths were thin on the ground at the time.

Rosetta lander on comet surface Comets - something of a disaster As the centuries unfolded, what could be called the opposite view - that the comets were responsible for intense heat spells - also gained a considerable audience, though there was just as little truth in it. The natural philosophers went one further. They said comets lead to heat, heat to storms and storms to natural disasters. Pliny the Elder for example (born circa 23 AD) listed twelve cometary phenomena according to their external appearances. And he assigned one natural disaster to each class. The Christian Middle Ages no longer saw cometary phenomena as the blind raging of an even blinder nature, preferring to interpret them as signs from God. Theologians such as Saint Hildegard of Bingen (1098-1179) and Albert Magnus (1200-1280) cited holy scripture. The Book of Jeremiah for example (1:11,12), in which God caused a fearsome “rod of an almond tree” to appear in the sky, a symbol of the prophet’s empowerment.

Or again Luke 21:11: “And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven.” In 1066, Halley’s Comet appeared to many as a harbinger of the Norman conquest of Britain, so vividly portrayed in the Bayeux tapestry, with its scenes from the Battle of Hastings. The decisive step towards overturning the view that comets are atmospheric phenomena was taken in 1577 by Danish astronomer, Tycho Brahe. For two and a half months he observed from his observatory in Uranienburg the progress of a comet across the heavens. Relying on the phenomenon of the daily parallax - an apparent “shuddering” motion of heavenly bodies in fact attributable to the observer’s position on the revolving Earth - he was able to establish that the comet had to be located beyond the lunar orbit.

Halley discovers an elliptical orbit Comet Halley's nucleus as seen by Giotto The scientific description of comets took another major step forward in 1705 thanks to the work of the British astronomer and physicist, Edmond Halley, a friend and patron of Isaac Newton. Investigating recorded comet measurements, he observed that the orbits of a number of bright comets were very similar: his own calculation of the orbit of a comet observed in 1682 coincided with the data recorded by Johannes Kepler in 1607 and by Apianus in 1531. He concluded that various comet observations were attributable to one and the same comet. Halley was proved right when in December 1758, the comet whose return he had predicted, thenceforth named after him, did indeed make a repeat appearance. This confirmed his theory that apparently parabolic comet orbits were in fact “simply” sections of one enormous elliptical orbit. Since then observations recorded in China in 240 BC have been identified as relating to a sighting of Halley’s comet, the oldest known document dealing with this phenomenon.

What was described in the Bible as a sign from God was seen by Fred Hoyle, the British astrophysicist, as a possible explanation for the great hiatal breaks in history. He took the view that such extraordinary developments as the extinction of the mammoth were attributable to strikes by comet fragments. His views incorporated the theory advanced by British astronomers Victor Clube and Bill Napier in 1982 that a giant comet was trapped by our solar system 15000 years ago. With the return of that comet every 1600 years, the accompanying debris - so the argument goes - prompted some of the world’s great turning points. This might also be an explanation for such legends as the Flood. A lump of icy sludge So what does the actual nucleus of a comet look like? One answer was supplied by the Giotto space probe in a mission masterminded by ESA. The probe was named after the major Italian painter Giotto di Bondone, who, in the early 14th century, portrayed a comet in his fresco in the Scrovegni Chapel in Padua.

On 14 March 1986, the probe succeeded in taking 100-metre-resolution pictures of the nucleus of Halley’s Comet from only 600 kilometres away. In the words of Uwe Keller: “The mission forced us to revisit our long-standing image of a comet nucleus as a ‘dirty snowball’. The pictures showed that it was more like a lump of icy sludge. The solid part of the nucleus is much larger than the icy part.” Bur hardly had Giotto trained its electronic eye on the heavenly body than the photo opportunity was already over; a dust particle measuring about a millimetre hit the probe. As the velocity differential between probe and comet was at that point 68.4 km per second, the force of the involuntary encounter was enough to put paid to any further snapshots. All the same, despite the damage to the camera, it proved possible to go on with the mission. Following two periods of “hibernation”, Giotto achieved a successful flyby of the Grigg-Skjellerup comet on 10 July 1992. Rosetta should now bring us entirely new knowledge about comet nuclei.

It will orbit the comet and deposit a small lander probe on its surface. So for the first time in history a comet travelling sunwards will be investigated from close quarters. For further information on Rosetta see For more on ESA Science missions see For further information, please contact: ESA, Media Relations Service Spaceflight Now | Ariane Launch Report | Comets: Once a myth, now an object of study Comets: Once a myth, now an object of study EUROPEAN SPACE AGENCY NEWS RELEASE Posted: February 24, 2004 In February 2004, Rosetta will be setting off on its long journey through our solar system to meet up with Comet Churyumov-Gerasimenko. It will take the European Space Agency (ESA) space probe ten years to reach its destination. The comet, which moves in an elliptical orbit around the Sun, will at rendezvous be some 675 million kilometres from the Sun, near the point in its orbit farthest from the Sun.

The meeting point was not chosen at random: at this point the comet is still barely active, it is still in fact a frozen lump of ice and interplanetary dust, in all probability the matter from which our solar system emerged four and a half billion years ago. Rosetta's job is to find out more about these strange bodies that travel through our solar system. As it moves on, the comet will begin to change. As it approaches the Sun, it will - like all comets - become active: in the warmth of the Sun's rays, the ices evaporate, tearing small dust particles from the surface. This produces the comet head (the coma) and tail. Only these two phenomena are visible from Earth. The comet nucleus itself is far too tiny - Churyumov-Gerasimenko measures about 4 kilometres across - to be viewed from Earth. As Dr Uwe Keller of the Max Planck Institute for Aeronomy in Kaltenburg-Lindau, the scientist responsible for the Osiris camera carried by Rosetta, explains, "Formation of the coma and tail during solar flyby skims several metres of matter off the comet's surface.

In the case of a small comet like Churyumov-Gerasimenko, the shrinkage is a good 1% each time round." As it flies past the Sun every 6.6 years it can look forward to a short future, especially on a cosmic timescale. Comets - a mystical view Visible cometary phenomena have fascinated human beings from time immemorial - and frightened them too. Even today mystical explanations prevail among some of the Earth's peoples. The Andaman islanders, a primitive people living in the Gulf of Bengal, see comets as burning torches hurled into the air by forest spirits - the more easily to detect humans foolish enough to stay out at night. For some Australian aborigines, comets are flaming sticks ridden by mighty shamans. Efforts to provide a scientific explanation of the 'cometa aster' ('hairy star') phenomenon stretch back to ancient times. A widely held view was that comets were in some way connected with processes at work in the atmosphere. In Meteorologica, Aristotle (384-322 BC) described how inflammable gases escape from clefts in rocks, collect in the upper layers of the sub-lunar world ('world under the Moon') and ignite.

Rapid release of such gases produced a shooting star; when let out slowly, they gave rise to a comet. That was Aristotle's best shot - and he was well aware of his limited insight into the question. As he himself acknowledged: "As we have no demonstrable basis for assertions about comets, I have to settle for an interpretation that does not conflict with established truths." Admittedly such truths were thin on the ground at the time. Comets - something of a disaster As the centuries unfolded, what could be called the opposite view - that the comets were responsible for intense heat spells - also gained a considerable audience, though there was just as little truth in it. The natural philosophers went one further. They said comets lead to heat, heat to storms and storms to natural disasters. Pliny the Elder for example (born circa 23 AD) listed twelve cometary phenomena according to their external appearances. And he assigned one natural disaster to each class. The Christian Middle Ages no longer saw cometary phenomena as the blind raging of an even blinder nature, preferring to interpret them as signs from God.

Theologians such as Saint Hildegard of Bingen (1098-1179) and Albert Magnus (1200-1280) cited holy scripture. The Book of Jeremiah for example (1:11,12), in which God caused a fearsome "rod of an almond tree" to appear in the sky, a symbol of the prophet's empowerment. Or again Luke 21:11: "And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven." In 1066, Halley's Comet appeared to many as a harbinger of the Norman conquest of Britain, so vividly portrayed in the Bayeux tapestry, with its scenes from the Battle of Hastings. The decisive step towards overturning the view that comets are atmospheric phenomena was taken in 1577 by Danish astronomer, Tycho Brahe. For two and a half months he observed from his observatory in Uranienburg the progress of a comet across the heavens.

Relying on the phenomenon of the daily parallax - an apparent "shuddering" motion of heavenly bodies in fact attributable to the observer's position on the revolving Earth - he was able to establish that the comet had to be located beyond the lunar orbit. Halley discovers an elliptical orbit The scientific description of comets took another major step forward in 1705 thanks to the work of the British astronomer and physicist, Edmond Halley, a friend and patron of Isaac Newton. Investigating recorded comet measurements, he observed that the orbits of a number of bright comets were very similar: his own calculation of the orbit of a comet observed in 1682 coincided with the data recorded by Johannes Kepler in 1607 and by Apianus in 1531. He concluded that various comet observations were attributable to one and the same comet. Halley was proved right when in December 1758, the comet whose return he had predicted, thenceforth named after him, did indeed make a repeat appearance. This confirmed his theory that apparently parabolic comet orbits were in fact "simply" sections of one enormous elliptical orbit.

Since then observations recorded in China in 240 BC have been identified as relating to a sighting of Halley's comet, the oldest known document dealing with this phenomenon. What was described in the Bible as a sign from God was seen by Fred Hoyle, the British astrophysicist, as a possible explanation for the great hiatal breaks in history. He took the view that such extraordinary developments as the extinction of the mammoth were attributable to strikes by comet fragments. His views incorporated the theory advanced by British astronomers Victor Clube and Bill Napier in 1982 that a giant comet was trapped by our solar system 15000 years ago. With the return of that comet every 1600 years, the accompanying debris - so the argument goes - prompted some of the world's great turning points. This might also be an explanation for such legends as the Flood. A lump of icy sludge So what does the actual nucleus of a comet look like? One answer was supplied by the Giotto space probe in a mission masterminded by ESA.

The probe was named after the major Italian painter Giotto di Bondone, who, in the early 14th century, portrayed a comet in his fresco in the Scrovegni Chapel in Padua. On 14 March 1986, the probe succeeded in taking 100-metre-resolution pictures of the nucleus of Halley's Comet from only 600 kilometres away. In the words of Uwe Keller: "The mission forced us to revisit our long-standing image of a comet nucleus as a 'dirty snowball'. The pictures showed that it was more like a lump of icy sludge. The solid part of the nucleus is much larger than the icy part." Bur hardly had Giotto trained its electronic eye on the heavenly body than the photo opportunity was already over; a dust particle measuring about a millimetre hit the probe. As the velocity differential between probe and comet was at that point 68.4 km per second, the force of the involuntary encounter was enough to put paid to any further snapshots. All the same, despite the damage to the camera, it proved possible to go on with the mission.

Following two periods of "hibernation", Giotto achieved a successful flyby of the Grigg-Skjellerup comet on 10 July 1992. Rosetta should now bring us entirely new knowledge about comet nuclei. It will orbit the comet and deposit a small lander probe on its surface. So for the first time in history a comet travelling sunwards will be investigated from close quarters. Flight data file eLearn.Punjab Portal | Read Book Source & Credit : Jaxchessnews Page 2 Do you know that all stars, the Sun, the Moon, the Earth , all planets and satellites are called heavenly bodies? The heavenly bodies are moving in unimaginable vast space – universe. The Sun, the planets, and their moons are the largest objects in the solar system. But asteroids and comets are the smaller parts of the solar system. We have already studied about the solar system and planets. In this chapter, we shall study other members of the solar system. Satellites Any heavenly body that moves around a planet is called a satellite. The Moon is a natural satellite of the Earth that orbits the Earth (Fig.12.1).

Mars, Jupiter, Saturn, Uranus and Neptune have their own satellites too. Natural Satellites Beside moons of the planets, some other natural satellites are also moving around the Sun. These are asteroids, comets and meteoroids. Some of them can be seen from the Earth. Asteroids An asteroid is a piece of rock that orbits the Sun between Mars and Jupiter. The astronomers have discovered thousands of asteroids. Asteroids are made of rock, metals or minerals. Most of the asteroids orbit the Sun between Mars and Jupiter in a wide band (Fig.12.2). This band is called the asteroid belt. The asteroid belt is about 15 hundred thousand kilometres wide. Asteroids come in all shapes and sizes. Some asteroids have diameter up to 1,000 kilometres but some are very small in diameter. Fig.12.1: The Moon is the natural satellite of the Earth. Fig.12.2: Asteroid belt between Mars and Jupiter Fig.12.5: During orbiting near the Sun a comet bears a long tail of gases. • Comets far away from the Sun bear no tail. Most of the time comets remain far away from the Sun.

A comet known as Comet Halley has appeared in the sky many times. It appears after every 76 years. It was seen in 1986 for the last time. When can we expect to see Comet Halley again? People in the past had been sighting the Comet Halley in different ways. Some people sighted it as a long-haired star. Some sighted it as having a tail streaming like smoke up to nearly half the sky. Some sighted it as having a tail like a broom or like the blade of sword. To some people it looked like a dragon with multiple tails. Many people were also afraid of this comet. European scientists sent a space probe Giotto to meet Comet Halley in 1985-86. Giotto sent many pictures of the Comet Halley back to the Earth. Its head was black in colour. As the Giotto moved through the coma of the comet, it was struck by the particles of ice and dust. Page 5 Meteors Uncountable number of small heavenly bodies also orbit the Sun. These are called meteoroids. A meteoroid is a piece of rock or metal that orbits the Sun. Meteoroids are scattered in different orbits in space.

Most of them are too small to be seen from the Earth. Have you ever seen a shooting star or fireball in the sky? In fact, it is not a star but a meteoroid entering the atmosphere of the Earth. Due to the friction of air, it gets fire (Fig.12.6). A meteoroid when enters the atmosphere of our Earth, it is called a meteor. A meteor is a stray particle which comes from the asteroid belt and enters the atmosphere of the Earth. Due to the friction of air, the meteor gets fire and a trail of light is seen. Some people call them falling stars, shooting stars, or fireballs. We can view 20 to 30 meteors on a clear night. But we have to move away from the glare of city lights. Most meteors entering our atmosphere burn up 50 to 100 kilometres above the surface of the Earth. It adds tons of dust into our atmosphere everyday. Sometimes a few big enough meteoroids do strike Earth’s surface. These are called meteorites. A meteorite is a meteor that strikes Earth’s surface. Activity 12.2 1. Place a magnet inside a clear plastic bag.

Then move the bag-covered magnet through the rainwater your teacher has collected. 2. Use a hand lens to look carefully at the outside of the bag. If you find any small spheres, or round objects, use a stick to scrape them onto a microscope slide. 3. Observe the objects through a microscope. If they still look like round objects, what you probably have are meteorites–pieces of space dust that came to Earth as falling stars! Things to think: What might cause most meteorites to be rounded in shape? Artificial Satellites There are many man-made satellites orbiting the Earth. These are called artificial satellites. Artificial satellites are very important for mankind. The first artificial satellite was sent by Russia in 1957. It was named Sputnik-1 (Fig.12.8). Launching of this satellite opened new horizons for the scientists. After a few years of launching Sputnik-1, Russia sent Yuri Gagarin, the first man into space. Since then, thousands of satellites have been sent into space. Source & Credit : Spacesim Orbits of Artificial Satellites: Artificial satellites move around the Earth in different orbits.

Some orbits are given here: Geostationary Orbit: The orbit in which an artificial satellite completes its one orbit in the same time that the Earth takes to complete one spin, i.e. 24 hours, is called geostationary orbit. A satellite in this orbit looks stationary from the Earth. Polar Orbit: Polar orbit passes over the north and south poles of the Earth. So, satellites moving in this orbit can scan the whole Earth during their motion. Eccentric Orbit: The scientific satellites move in eccentric orbit to measure magnetism and electric fields of the Earth. Low Earth Orbit: This orbit is very close to the Earth. Low Earth orbit is used by space shuttles, space stations and the Hubble Telescope. These satellites may orbit the Earth every 90 minutes. Satellite Receiving Station: A station on the Earth that receives messages from the satellites is called a satellite receiving station. Kinds of Artificial Satellites Scientists have sent many satellites which move around the Earth. These satellites help scientists to learn about weather and many more things on the Earth. Sputnik-I On October 4, 1957, Russia sent the world’s first artificial satellite, Sputnik-1 into space.

The name comes from a Russian word for “travelling companion of the world.” It weighed just 83 kg. It carried a thermometer and two radio transmitters which sent information about the atmosphere to the Earth. Its two transmitters only functioned for 21 days. After 57 days in orbit, it was destroyed. Explorer 1 Explorer 1 was the first satellite launched by the United States of America. It was sent into space on January 31, 1958. It weighed only 14kg. Explorer 1 sent information about the radiation environment in Earth orbit. Geostationary Satellites Geostationary satellites move at a height of about 36,000 km above the Earth. At this height they move around the Earth at the same speed as the Earth moves around its axis. This satellite seems to be stationary. They are used as communication satellites. Pakistan has launched its first geostationary satellite, PAKSAT–1R on August 11, 2011. Landsat Satellites The Landsat satellites is a series of satellite missions. Since 1972, Landsat satellites have collected information about Earth from space.

Landsat satellites have taken photographs of Earth’s continents and surrounding coastal regions. Page 9 Communication Satellites Communication satellites have a great effect on our daily lives. They link remote areas of the Earth with telephone and television. Newspapers are typed and transmitted to printing machines via satellite in some countries. Polar Satellite Polar satellite was launched on February 24, 1996 by America. Polar satellite studies atmosphere of the Earth in polar orbit after every 18 hours. Polar satellite will help scientists to protect future satellites from atmospheric dangers. Fig.12.11: This telecom satellite passes telephone essages from one side of the world tothe other. Global Positioning System Satellites have improved our knowledge about space and even about our Earth. Using satellites, you can find your position anywhere in the world accurate to 10m or less. Locating the position of objects with the help of a satellite is called the Global Positioning System or GPS. It is freely accessible by anyone with a GPS receiver. Visiting The Space • In 1969, two Americans were the first men to step on the Moon. They were Neil Armstrong and Edwin Aldrin.

• India sent her first satellite Aryabhatta into space in 1975. • Pakistan sent her satellite Badr-I in 1990s. 1. Any heavenly body that moves around a planet is called a satellite. 2. Asteroids are discovered moving between Mars and Jupiter. 3. A comet is a heavenly body made of ice and dust particles. It has three parts; a head, coma and a tail. 4. Meteoroids are pieces of rock or metal. They also orbit the Sun. 5. Man-made satellites orbiting the Earth are called artificial satellites. Sputnik, Explorer 1, Communication and Polar are different kinds of artificial satellites. 6. Artificial satellites move around the Earth in different orbits. 7. A rocket is used to launch a satellite into space. Science Projects 1. Fill a tray with flour. From a height, drop a small stone into it. Carefully remove the stone to see the crater it has made. How are craters formed on the surface of the Moon? 2. On a table next to a window place a shaving mirror facing the Moon. Place another mirror opposite the first one facing inwards.

Take a magnifying glass in your hand and stand at an angle from where you can see the Moon in the mirror facing inwards. Raise the magnifying glass and through it see a magnified (larger) view of the Moon in the mirror facing inwards. Caution: Do not try to observe the Sun using this experiment. It can damage your eyesight. Today there is a large telescope in orbit around the Earth. Its name is the Hubble Space Telescope. Even though the mirror in the Hubble Space Telescope is smaller than that of many telescopes on the Earth, it can see more clearly. Why does the Hubble Telescope takes clearer pictures than telescopes on Earth? Why do you think there is a need of such telescopes in space? Once a myth, now an object of study | Times Higher Education (THE) Times Higher Education (THE) Last Name * Email * A valid e-mail address. All e-mails from the system will be sent to this address. The e-mail address is not made public and will only be used if you wish to receive a new password or wish to receive certain news or notifications by e-mail.

Password Higher education updates from the THE editorial team World University Rankings news New offers, products and services from THE/TES Global Choose your profile * Once a myth, now an object of study February 24, 2004 Share on linkedin Paris, 23 Feb 2004 On 26 February, Rosetta will be setting off on its long journey through our solar system to meet up with Comet Churyumov-Gerasimenko. It will take the European Space Agency (ESA) space probe ten years to reach its destination. The comet, which moves in an elliptical orbit around the Sun, will at rendezvous be some 675 million kilometres from the Sun, near the point in its orbit farthest from the Sun. The meeting point was not chosen at random: at this point the comet is still barely active, it is still in fact a frozen lump of ice and interplanetary dust, in all probability the matter from which our solar system emerged four and a half billion years ago. Rosetta's job is to find out more about these strange bodies that travel through our solar system. As it moves on, the comet will begin to change.

As it approaches the Sun, it will - like all comets - become active: in the warmth of the Sun's rays, the ices evaporate, tearing small dust particles from the surface. This produces the comet head (the coma) and tail during solar flyby skims several metres of matter off the comet's surface. In the case of a small comet like Churyumov-Gerasimenko, the shrinkage is a good 1% each time round." As it flies past the Sun every 6.6 years it can look forward to a short future, especially on a cosmic timescale. Comets - a mystical view Visible cometary phenomena have fascinated human beings from time immemorial – and frightened them too. Even today mystical explanations prevail among some of the Earth's peoples. The Andaman islanders, a primitive people living in the Gulf of Bengal, see comets as burning torches hurled into the air by forest spirits – the more easily to detect humans foolish enough to stay out at night. For some Australian aborigines, comets are flaming sticks ridden by mighty shamans. Efforts to provide a scientific explanation of the 'cometa aster' ('hairy star') phenomenon stretch back to ancient times.

A widely held view was that comets were in some way connected with processes at work in the atmosphere. In Meteorologica, Aristotle (384-322 BC) described how inflammable gases escape from clefts in rocks, collect in the upper layers of the sub-lunar world ('world under the Moon') and ignite. Rapid release of such gases produced a shooting star; when let out slowly, they gave rise to a comet. That was Aristotle's best shot - and he was well aware of his limited insight into the question. As he himself acknowledged: "As we have no demonstrable basis for assertions about comets, I have to settle for an interpretation that does not conflict with established truths." Admittedly such truths were thin on the ground at the time. Comets - something of a disaster As the centuries unfolded, what could be called the opposite view - that the comets were responsible for intense heat spells - also gained a considerable audience, though there was just as little truth in it. The natural philosophers went one further. They said comets lead to heat, heat to storms and storms to natural disasters.

Pliny the Elder for example (born circa 23 AD) listed twelve cometary phenomena according to their external appearances. And he assigned one natural disaster to each class. The Christian Middle Ages no longer saw cometary phenomena as the blind raging of an even blinder nature, preferring to interpret them as signs from God. Theologians such as Saint Hildegard of Bingen (1098-1179) and Albert Magnus (1200-1280) cited holy scripture. The Book of Jeremiah for example (1:11,12), in which God caused a fearsome "rod of an almond tree" to appear in the sky, a symbol of the prophet's empowerment. Or again Luke 21:11: "And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven." In 1066, Halley's Comet appeared to many as a harbinger of the Norman conquest of Britain, so vividly portrayed in the Bayeux tapestry, with its scenes from the Battle of Hastings.

The decisive step towards overturning the view that comets are atmospheric phenomena was taken in 1577 by Danish astronomer, Tycho Brahe. For two and a half months he observed from his observatory in Uranienburg the progress of a comet across the heavens. Relying on the phenomenon of the daily parallax - an apparent "shuddering" motion of heavenly bodies in fact attributable to the observer's position on the revolving Earth - he was able to establish that the comet had to be located beyond the lunar orbit. Halley discovers an elliptical orbit The scientific description of comets took another major step forward in 1705 thanks to the work of the British astronomer and physicist, Edmond Halley, a friend and patron of Isaac Newton. Investigating recorded comet measurements, he observed that the orbits of a number of bright comets were very similar: his own calculation of the orbit of a comet observed in 1682 coincided with the data recorded by Johannes Kepler in 1607 and by Apianus in 1531. He concluded that various comet observations were attributable to one and the same comet.

Halley was proved right when in December 1758, the comet whose return he had predicted, thenceforth named after him, did indeed make a repeat appearance. This confirmed his theory that apparently parabolic comet orbits were in fact "simply" sections of one enormous elliptical orbit. Since then observations recorded in China in 240 BC have been identified as relating to a sighting of Halley's comet, the oldest known document dealing with this phenomenon. What was described in the Bible as a sign from God was seen by Fred Hoyle, the British astrophysicist, as a possible explanation for the great hiatal breaks in history. He took the view that such extraordinary developments as the extinction of the mammoth were attributable to strikes by comet fragments. His views incorporated the theory advanced by British astronomers Victor Clube and Bill Napier in 1982 that a giant comet was trapped by our solar system 15000 years ago. With the return of that comet every 1600 years, the accompanying debris - so the argument goes - prompted some of the world's great turning points. This might also be an explanation for such legends as the Flood.

A lump of icy sludge So what does the actual nucleus of a comet look like? One answer was supplied by the Giotto space probe in a mission masterminded by ESA. The probe was named after the major Italian painter Giotto di Bondone, who, in the early 14th century, portrayed a comet in his fresco in the Scrovegni Chapel in Padua. On 14 March 1986, the probe succeeded in taking 100-metre-resolution pictures of the nucleus of Halley's Comet from only 600 kilometres away. In the words of Uwe Keller: "The mission forced us to revisit our long-standing image of a comet nucleus as a 'dirty snowball'. The pictures showed that it was more like a lump of icy sludge. The solid part of the nucleus is much larger than the icy part." Bur hardly had Giotto trained its electronic eye on the heavenly body than the photo opportunity was already over; a dust particle measuring about a millimetre hit the probe. As the velocity differential between probe and comet was at that point 68.4 km per second, the force of the involuntary encounter was enough to put paid to any further snapshots.

All the same, despite the damage to the camera, it proved possible to go on with the mission. Following two periods of "hibernation", Giotto achieved a successful flyby of the Grigg-Skjellerup comet on 10 July 1992. Rosetta should now bring us entirely new knowledge about comet nuclei. It will orbit the comet and deposit a small lander probe on its surface. So for the first time in history a comet travelling sunwards will be investigated from close quarters. For further information on Rosetta see For more on ESA Science missions see For further information, please contact: ESA, Media Relations Service Once a myth, now an object of study | EurekAlert! Science News Once a myth, now an object of study European Space Agency Print E-Mail The comet, which moves in an elliptical orbit around the Sun, will at rendezvous be some 675 million kilometres from the Sun, near the point in its orbit farthest from the Sun.

The meeting point was not chosen at random: at this point the comet is still barely active, it is still in fact a frozen lump of ice and interplanetary dust, in all probability the matter from which our solar system emerged four and a half billion years ago. Rosetta's job is to find out more about these strange bodies that travel through our solar system. As it moves on, the comet will begin to change. As it approaches the Sun, it will - like all comets - become active: in the warmth of the Sun's rays, the ices evaporate, tearing small dust particles from the surface. This produces the comet head (the coma) and tail during solar flyby skims several metres of matter off the comet's surface. In the case of a small comet like Churyumov-Gerasimenko, the shrinkage is a good 1% each time round." As it flies past the Sun every 6.6 years it can look forward to a short future, especially on a cosmic timescale. Comets - a mystical view Visible cometary phenomena have fascinated human beings from time immemorial - and frightened them too. Even today mystical explanations prevail among some of the Earth's peoples.

The Andaman islanders, a primitive people living in the Gulf of Bengal, see comets as burning torches hurled into the air by forest spirits - the more easily to detect humans foolish enough to stay out at night. For some Australian aborigines, comets are flaming sticks ridden by mighty shamans. Efforts to provide a scientific explanation of the 'cometa aster' ('hairy star') phenomenon stretch back to ancient times. A widely held view was that comets were in some way connected with processes at work in the atmosphere. In Meteorologica, Aristotle (384-322 BC) described how inflammable gases escape from clefts in rocks, collect in the upper layers of the sub-lunar world ('world under the Moon') and ignite. Rapid release of such gases produced a shooting star; when let out slowly, they gave rise to a comet. That was Aristotle's best shot - and he was well aware of his limited insight into the question. As he himself acknowledged: "As we have no demonstrable basis for assertions about comets, I have to settle for an interpretation that does not conflict with established truths." Admittedly such truths were thin on the ground at the time.

Comets - something of a disaster As the centuries unfolded, what could be called the opposite view - that the comets were responsible for intense heat spells - also gained a considerable audience, though there was just as little truth in it. The natural philosophers went one further. They said comets lead to heat, heat to storms and storms to natural disasters. Pliny the Elder for example (born circa 23 AD) listed twelve cometary phenomena according to their external appearances. And he assigned one natural disaster to each class. The Christian Middle Ages no longer saw cometary phenomena as the blind raging of an even blinder nature, preferring to interpret them as signs from God. Theologians such as Saint Hildegard of Bingen (1098-1179) and Albert Magnus (1200-1280) cited holy scripture. The Book of Jeremiah for example (1:11,12), in which God caused a fearsome "rod of an almond tree" to appear in the sky, a symbol of the prophet's empowerment.

Or again Luke 21:11: "And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven." In 1066, Halley's Comet appeared to many as a harbinger of the Norman conquest of Britain, so vividly portrayed in the Bayeux tapestry, with its scenes from the Battle of Hastings. The decisive step towards overturning the view that comets are atmospheric phenomena was taken in 1577 by Danish astronomer, Tycho Brahe. For two and a half months he observed from his observatory in Uranienburg the progress of a comet across the heavens. Relying on the phenomenon of the daily parallax - an apparent "shuddering" motion of heavenly bodies in fact attributable to the observer's position on the revolving Earth - he was able to establish that the comet had to be located beyond the lunar orbit. Halley discovers an elliptical orbit The scientific description of comets took another major step forward in 1705 thanks to the work of the British astronomer and physicist, Edmond Halley, a friend and patron of Isaac Newton.

Investigating recorded comet measurements, he observed that the orbits of a number of bright comets were very similar: his own calculation of the orbit of a comet observed in 1682 coincided with the data recorded by Johannes Kepler in 1607 and by Apianus in 1531. He concluded that various comet observations were attributable to one and the same comet. Halley was proved right when in December 1758, the comet whose return he had predicted, thenceforth named after him, did indeed make a repeat appearance. This confirmed his theory that apparently parabolic comet orbits were in fact "simply" sections of one enormous elliptical orbit. Since then observations recorded in China in 240 BC have been identified as relating to a sighting of Halley's comet, the oldest known document dealing with this phenomenon. What was described in the Bible as a sign from God was seen by Fred Hoyle, the British astrophysicist, as a possible explanation for the great hiatal breaks in history. He took the view that such extraordinary developments as the extinction of the mammoth were attributable to strikes by comet fragments.

His views incorporated the theory advanced by British astronomers Victor Clube and Bill Napier in 1982 that a giant comet was trapped by our solar system 15000 years ago. With the return of that comet every 1600 years, the accompanying debris - so the argument goes - prompted some of the world's great turning points. This might also be an explanation for such legends as the Flood. A lump of icy sludge So what does the actual nucleus of a comet look like? One answer was supplied by the Giotto space probe in a mission masterminded by ESA. The probe was named after the major Italian painter Giotto di Bondone, who, in the early 14th century, portrayed a comet in his fresco in the Scrovegni Chapel in Padua. On 14 March 1986, the probe succeeded in taking 100-metre-resolution pictures of the nucleus of Halley's Comet from only 600 kilometres away. In the words of Uwe Keller: "The mission forced us to revisit our long-standing image of a comet nucleus as a 'dirty snowball'. The pictures showed that it was more like a lump of icy sludge.

The solid part of the nucleus is much larger than the icy part." Bur hardly had Giotto trained its electronic eye on the heavenly body than the photo opportunity was already over; a dust particle measuring about a millimetre hit the probe. As the velocity differential between probe and comet was at that point 68.4 km per second, the force of the involuntary encounter was enough to put paid to any further snapshots. All the same, despite the damage to the camera, it proved possible to go on with the mission. Following two periods of "hibernation", Giotto achieved a successful flyby of the Grigg-Skjellerup comet on 10 July 1992. Rosetta should now bring us entirely new knowledge about comet nuclei. It will orbit the comet and deposit a small lander probe on its surface. So for the first time in history a comet travelling sunwards will be investigated from close quarters. ###

Question: Which heavenly body was Giotto sent to photograph in 1986?`
Answer: Halley’s Comet