Beginners Astronomy

The Solar System Beginners Astronomy Martin Crow Crayford Manor House Astronomical Society

The Solar System This week: The Solar System from a historical point of view How the Ancients viewed the Solar System \ Universe The Greeks view and their influence Copernicus, Tycho, Galileo, Kepler and our modern view of the Solar System. Martin Crow Crayford Manor House Astronomical Society

The Solar System How the Ancients viewed the Solar System \ Universe For ancient people there was no Solar System it was the sky. The sky was their clock / calendar The appearance of certain constellations would herald the change of the seasons and the appearance \ disappearance of certain animals. Martin Crow Crayford Manor House Astronomical Society

The Solar System With the advent of agriculture the observing the sky became even more important for timing the planting of crops. In ancient Egypt the heliacal rising of Sirius occurred close to the time of the Nile’s inundation and so seed needed planting. This also marked the beginning of their New Year. Heliacal rising means: when a star, that has not been visible for a while, is visible just before the Sun rises. This is weather dependent. Martin Crow Crayford Manor House Astronomical Society

The Solar System Martin Crow Crayford Manor House Astronomical Society

The Solar System The Greeks view and their influence Eudoxus (410?BC – 350?BC) Eudoxus developed a two sphere model. It divided the Cosmos into two regions: a spherical Earth central and motionless and a spherical heavenly realm centred on the Earth containing multiple rotating crystalline spheres. Each sphere carried a planet in the order: Moon, Sun, Venus, Mercury, Mars, Jupiter, Saturn, Fixed Stars This Eudoxan system had a number of critical flaws: It predicted motions poorly. It could not account for the planets retrograde motions and it couldn’t account for the planets change in brightness. Martin Crow Crayford Manor House Astronomical Society

The Solar System Martin Crow Crayford Manor House Astronomical Society

The Solar System 384 BC – 322 BC Aristotle’s world view The five elements: Fire, which is hot and dry Earth, which is cold and dry Air, which is hot and wet Water, which is cold and wet Aether, which is the divine substance that makes up the heavenly spheres and heavenly bodies Martin Crow Crayford Manor House Astronomical Society

The Solar System Apollonius of Perga (262 BC – 190 BC) In response to some of the problems with the Eudoxan system he introduced two mechanisms that allowed a planet to vary its distance and speed. Eccentric Deferent and Epicycle Martin Crow Crayford Manor House Astronomical Society

The Solar System Aristarchus of Samos (310 BC – 230 BC) Aristarchus proposed a system where the Earth revolved around the Sun This was not well received as it meant that the Earth moved !!!! The Greeks knew that the Earth was a sphere and how big that it was. It was obvious that we would all be thrown off if this was the case. Martin Crow Crayford Manor House Astronomical Society

The Solar System Claudius Ptolemy (90 AD – 168 AD) a Roman citizen of Egypt Ptolemy wrote the Almagest around 150 AD and is a critical source of information on Greek astronomy Ptolemy claimed to have derived his geometrical models from selected astronomical observations by his predecessors spanning more than 800 years. Ptolemy presented his astronomical models in convenient tables which could be used to compute the future or past position of the planets. The Almagest also contains a star catalogue which is an appropriated version of a catalogue created by Hipparchus. Martin Crow Crayford Manor House Astronomical Society

The Solar System The Ptolemaic system said: The Earth was chaotic. The heavens were unchanging. The heavenly bodies moved only in perfect circles. The retrograde motions of the planets were accounted for by the use of eccentrics, deferents and epicycles. Martin Crow Crayford Manor House Astronomical Society

The Solar System The Ptolemaic system Note that the order of the planets has changed slightly from the Eudoxan system Martin Crow Crayford Manor House Astronomical Society

The Solar System The Antikthera mechanism Martin Crow Crayford Manor House Astronomical Society

The Solar System Ptolemaic science was lost in Europe but kept alive and advanced upon in the middle East. Links with the Arab world brought Ptolemy back to Europe in the Middle ages. The Geocentric system lasted until well into the 17th century Martin Crow Crayford Manor House Astronomical Society

The Solar System The beginnings of our modern understanding Nicolaus Copernicus (1473 – 1543) Although generally thought of as the author of the Heliocentric system Copernicus was to a large extent reworking earlier Greek ideas. Although he put the Sun at the centre of the Universe the planets were all still required to orbit in perfect circles as in the Greek tradition. Because of this the predictive abilities of this model were no better than the old Ptolemaic system. It did account for the daily motion of the Sun, Moon and star plus the retrograde motion of the Planets and the seasons. Martin Crow Crayford Manor House Astronomical Society

The Heliocentric system The beginnings of our modern understanding Martin Crow Crayford Manor House Astronomical Society

The Solar System His book ‘De revolutionibus orbium coelestium’ was not published until after his death in 1543. Copernicus wasn’t accepted immediately or by all. Predictions were no better and how do you prove that the Earth moves? However, there was a growing appetite for change. In the medieval mind the ancients were seen as the pinnacle of human achievement and were infallible. The fact that dates predicted for Planetary apparition could be out by a couple of weeks indicated to some that the very mechanism of the universe was wearing out and the world was coming to an end. Martin Crow Crayford Manor House Astronomical Society

The Solar System Tycho Brahe (1546 – 1601) Tycho was probably the greatest pre-telescopic observer there had ever been. Tycho was a Danish nobleman and had been granted an estate on the island of Hven. Martin Crow Crayford Manor House Astronomical Society

The Solar System In 1572 Tycho observed a new star. His observations showed that it lacked parallax and therefore could not be a sub-lunar phenomenon. In ‘De nova Stella (on the new star) 1573 he refuted the theory of the celestial spheres in showing that the heavens were not unchanging. Tycho went on to demonstrate with comets seen in 1577, 1580, 1582, 1585, 1590, 1593 & 1594 that they also were at a great distance and not atmospheric phenomena. This also proved that the crystalline spheres did not exist. Martin Crow Crayford Manor House Astronomical Society

The Solar System Despite all of this Tycho still held that the Earth did not move but produced his own Tychonic system. Martin Crow Crayford Manor House Astronomical Society

The Solar System Galileo Galilei (1564 – 1642) With the invention of the telescope by Hans Lipperhey in 1608 Galileo made his own and pointed it towards the sky in 1609. With the aid of the telescope Galileo discovered: The moons of Jupiter - showing that it was a centre of rotation. The phases of Venus - demonstrating that it revolved around the Sun. That the wandering stars were other worlds. That there were stars that we could not see unaided. That the Sun’s surface sometimes had spots on it. Martin Crow Crayford Manor House Astronomical Society

The Solar System But none of these things actually proved that the Earth moved!!! Martin Crow Crayford Manor House Astronomical Society

The Solar System Johannes Kepler (1571 – 1630) Kepler was Tycho’s assistant for a short period in Prague prior to Tycho’s unexpected death in October 1601. Kepler was appointed imperial mathematician. Using Tycho’s observations of Mar’s motion he produced his three laws of Planetary motion. The first two laws were published in ‘Astronomia Nova’ 1609. The third law was not published until 1619. Martin Crow Crayford Manor House Astronomical Society

The Solar System Kepler’s three laws of planetary motion 1st Law The orbit of every planet is a conic section or ellipse with the Sun at one of the two foci. Martin Crow Crayford Manor House Astronomical Society

The Solar System 2nd Law A line joining a planet and the Sun sweeps out equal areas during equal intervals of time. Martin Crow Crayford Manor House Astronomical Society

The Solar System 3rd Law The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. What this means is that if you know an objects orbital period (i.e. how long it takes to go round once) you can work out the ratio of distances between the planets. Therefore, if you know the orbital radius of one planet you can work out the rest. Martin Crow Crayford Manor House Astronomical Society

The Solar System Isaac Newton (1643 – 1727) Newton published PhilosophiæNaturalis Principia Mathematica published in 1687. Normally referred to as ‘Principia’ it describes the three laws of motion, universal gravitation and demonstrated the consistency of Kepler’s three laws of planetary motion and his theory of gravitation. Newton showed why the planets moved as Kepler had discovered and helped to remove doubts about heliocentrism. Newtonian gravitational theory would hold sway for the next 250 years and is still used today. It did not prove that the Earth moved. Martin Crow Crayford Manor House Astronomical Society

The Solar System So how do you prove that the Earth moves? One way of proving that the Earth moved was to look for parallax in the stars. This method would also give a distance to the star. Martin Crow Crayford Manor House Astronomical Society

The Solar System How to look for stellar parallax and things to consider. The stars are at different distances. Assuming that all stars are the same brightness then the brighter the star the nearer it is and vice versa. The Ariel telescope is not suitable. Atmospheric refraction must be taken into account. The way forward is to use a Zenith telescope. Martin Crow Crayford Manor House Astronomical Society

The Solar System Robert Hooke (1635 – 1703) John Flamsteed (1646 – 1719) Astronomer Royal Both used a Zenith Telescope to look for parallax. The star they decided to study was Gamma Draconis. This star passes directly overhead and is relatively bight at mag 2.2. Martin Crow Crayford Manor House Astronomical Society

Gamma Draconis 2011 May 06 2:54ut • The Solar System Martin Crow Crayford Manor House Astronomical Society

The Solar System One of the telescopes used by Hooke still exists today and you may have been up it without realising. Completed in 1667 the Monument was designed as a scientific instrument. Sadly it was not up to the job as it expanded at different rates and swayed in the wind!! Martin Crow Crayford Manor House Astronomical Society

The Solar System Other zenith telescopes The well telescope Greenwich 1679 It would appear that it was not a success, probably because the tube and lenses were too unstable, the object glass was of poor quality and, as was said in 1737, ‘because of the damp of the place’. Martin Crow Crayford Manor House Astronomical Society

The Solar System The beginnings of our modern understanding James Bradley (1693 – 1762) Working with Samuel Molyneux trying to measure the parallax of Gamma Draconis they measured an apparent motion, but it was not as they expected it to be. What Bradley found was an apparent motion of 20” that reached its most southerly point in March, and its most northerly point in September and that could not be accounted for by parallax. This was at first a mystery. Allegedly, Bradley realised what was going on when sailing on the Thames and noticed the effect of the apparent wind when the boat changed direction. This was the discovery of the ‘Aberration of Light’ and was conclusive evidence that the Earth moved through space orbiting the Sun James Bradley published his results in the Philosophical Transactions in January 1729. It was to be another hundred years before stellar parallax was measured. Martin Crow Crayford Manor House Astronomical Society

The Solar System At last the we had left Ptolemy behind. So now we knew that: The Earth does move through space rotating as it does so. The seasons are caused by the tilt of the Earth’s axis. The Earth along with all of the known planets orbit the Sun. The orbits of planets and comets are all conic sections - elliptical. We now knew that this was all caused through the action of gravity and Newton’s laws of motion. Martin Crow Crayford Manor House Astronomical Society

The Solar System But how large is the solar system? From Kepler’s third law we knew the ratio of the distances. What was required was one accurately known distance. So how was this to be done? Martin Crow Crayford Manor House Astronomical Society

The Solar System Enter the transit of Venus. First predicted by Kepler in 1627 He said a transit of Venus would occur in 1631 and 1761 but could not accurately predict where it would be seen from i.e. Europe. Transits of Venus are very rare and occur in pairs with 8 year gaps separated by long gaps of 121.5 years and 105.5 years. Martin Crow Crayford Manor House Astronomical Society

The Solar System So why is the transit of Venus so important? If viewed from two widely spaced locations parallax can be used to determine the Earth - Sun distance. This method was first described by James Gregory (1638 – 1675) in Optica Promota in 1663. Martin Crow Crayford Manor House Astronomical Society

The Solar System Jeremiah Horrocks (1618 – 1641) corrected Kepler’s prediction of 1631 Showing that another would happen in 1639 at around 3:00 pm This was observed by Horrocks from Much Hoole near Preston and his friend William Crabtree from Salford on 4th December 1639. He estimated an Earth – Sun distance of 59.4 million miles which is approx 2/3 the actual distance but a more accurate figure than any suggested up to that time. Martin Crow Crayford Manor House Astronomical Society

The Solar System The transits of 1761 and 1769. International collaboration was organised so that observations could be made around the world. Scientists and explorers from Britain, Austria and France travelled to destinations around the world, including Siberia, Norway, Newfoundland and Madagascar. Captain Cooks voyage to the South seas was specifically to observe the transit of Venus although he managed to discover Australia while he was down there. Guillaume Le Gentil spent 8 years away from home and saw neither. Using the combined results from both events the French astronomer JeroneLalande calculated a value of 153 million kilometres ± 1 million km. The precision was less than expected due to the ‘black drop effect’. However, we now had a very good idea of the size of the solar system. Martin Crow Crayford Manor House Astronomical Society

The Solar System The black drop effect Martin Crow Crayford Manor House Astronomical Society

The Solar System Transit observations in 1874 and 1882 allowed this value to be refined further. The American astronomer Simon Newcomb combined the data from the last four transits and derived a value of 149.59 million kilometers (±0.31 million km). In 1931 an even more accurate figure was obtained by measuring the parallax of 433 Eros during its close opposition. The accuracy of this figure was not superceded until 1968 when radar techniques were used. Martin Crow Crayford Manor House Astronomical Society

The Solar System We observed the 2004 transit from the manor house in Crayford. Your last chance to see a transit will be 6th June 2012 just as the Sun rises. Martin Crow Crayford Manor House Astronomical Society

The Solar System Things had really changed but ‘our’ solar system still only contained the ‘classical’ planets. Martin Crow Crayford Manor House Astronomical Society

The Solar System William Herschel (1738 – 1822) In March 1781 while searching for double stars Herschel discovered an object which was not stellar in appearance and at first he thought it to be cometary in nature. Further observations showed that was a planet and orbited beyond Saturn. He had discovered Uranus. Interestingly, it was in approx. the position predicted by Bodes law. Martin Crow Crayford Manor House Astronomical Society

The Solar System Following on from Herschel's discovery a great effort went into looking for a possible planet between Mars and Jupiter also predicted by Bodes law. In 1801 Giuseppe Piazzi discovered Ceres the first of the asteroids. Martin Crow Crayford Manor House Astronomical Society

The Solar System Observations of Uranus’s orbit showed slight changes which it was deduced were due to gravitational perturbation of an unknown planet. On 23 September 1846 Johann Galle observed the planet Neptune which was within a degree of the position predicted by Urbain Le Verrier. Martin Crow Crayford Manor House Astronomical Society

The Solar System Perturbations in Neptune's orbit led to a search for Planet X as it was dubbed. In 1930 Clyde Tombaugh using photographic plates discovered Pluto the tenth planet. Martin Crow Crayford Manor House Astronomical Society

Martin Crow Crayford Manor House Astronomical Society

Beginners Astronomy