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Teachers Notes Booklet 1: Introduction to the Universe Page 1 of 19 The European Space Agency The European Space Agency (ESA) was formed on 31 May 1975. It currently has 17 Member States: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland & United Kingdom. The ESA Science Programme currently contains the following active missions: Venus Express – an exploration of our Cluster – a four spacecraft mission to sister planet. investigate Rosetta – first mission to fly alongside Sun and the Earth's magnetosphere and land on a comet XMM-Newton – an X-ray telescope Double Star – joint mission with the helping to solve cosmic mysteries Chinese to study the effect of the Sun Cassini-Huygens – a joint ESA/NASA on the Earth’s environment mission to investigate Saturn and its SMART-1 – Europe’s first mission to moon Titan, with ESA's Huygens probe the Moon, which will test solar-electric SOHO propulsion in flight, a key technology for atmosphere and interior future deep-space missions Hubble Space Telescope – world's Mars Express - Europe's first mission most important and successful orbital to Mars consisting of an orbital platform observatory searching for water and life on the Ulysses planet investigate the polar regions around the INTEGRAL – first space observatory to Sun - interactions new – views the first between of the the Sun's spacecraft to simultaneously observe celestial objects in gamma rays, X-rays and visible light Details on all these missions and others can be found at - http://sci.esa.int. Prepared by Anne Brumfitt Content Advisor Chris Lawton Science Editor, Content Advisor, Web Integration & Booklet Design Karen O'Flaherty Science Editor & Content Advisor Jo Turner Content Writer © 2005 European Space Agency Teachers Notes Booklet 1: Introduction to the Universe Page 2 of 19 Booklet 1 – Introduction to the Universe Contents 1.1 Solar System................................................................. 4 1.2 Planets and Moons ......................................................... 6 1.3 Asteroids and Comets..................................................... 9 1.4 Bodies of the Universe .................................................. 11 1.5 Stellar Clusters and Constellations.................................. 14 1.6 Relative Distances to Objects......................................... 15 1.7 Stellar Motions ............................................................ 16 1.8 Other Materials............................................................ 18 Tables 1.1 Distance and Orbital Parameters for the Planets ................. 7 1.2 Observational Characteristics of the Planets....................... 7 1.3 Dates of Primary Meteor Showers................................... 10 1.4 Brightest Open and Globular Star Clusters ....................... 14 Figures 1.1 Barringer Meteor Crater ................................................ 10 1.2 View of Orion and Actual Distance to Stars ...................... 14 1.3 Diurnal Stellar Motion ................................................... 16 Teachers Notes Booklet 1: Introduction to the Universe Page 3 of 19 1.1 Solar System The Solar System is a collection of planets, moons, asteroids and comets and other rocky objects orbiting the Sun. The Solar System is believed to extend out to at least 150 000 million km from the Sun, although the planets are all found within about 6000 million km. Our Solar System is thought to have formed 4.6 x 109 years ago from a vast, rotating cloud of gas and dust known as the solar nebula. As the solar nebula rotated, its gravity began to attract gas and dust towards the centre, eventually forming our Sun. The Sun The Sun is the powerhouse of the Solar System. Without it, life on Earth simply would not exist. Despite burning its hydrogen fuel for the best part of 5 billion years, the Sun is still only half way through its life cycle. The study of the Sun, its environment and how the material it discharges interacts with other worlds in the Solar System is of great interest to us all. ESA has a number of missions that analyse various aspects of this solar emission. Solar Missions SOHO is a space-based observatory viewing and investigating the Sun from its deep core, through to its outer atmosphere (the corona) and the powerful solar wind. This joint mission with NASA is being conducted from the inner Lagrange point allowing continuous monitoring of the Sun. The main scientific goal of the joint ESA-NASA Ulysses deepspace mission is to make the first-ever measurements of the unexplored region of space above the Sun's poles. Teachers Notes Booklet 1: Introduction to the Universe Page 4 of 19 The Cluster mission is currently investigating the small-scale structure (in three dimensions) of the Earth's plasma environment, such as those involved in the interaction between the solar wind and the magnetospheric plasma, by using four spacecraft flying in formation. The Double Star mission is a joint venture with the Chinese and like the Cluster mission it is studying the effects of the Sun on the Earth's environment. The mission consists of two spacecraft, one in a polar orbit and one in an equatorial orbit, which are based on the Cluster design. Teachers Notes Booklet 1: Introduction to the Universe Page 5 of 19 1.2 Planets and Moons The formation of the Sun had a dramatic effect on the temperatures across the solar nebula, introducing a temperature range that stretched from about 2000K near the Sun to less than 50K at the outer regions. The heat in the inner Solar System only allowed materials with high condensation temperatures to remain solid. These particles eventually gathered to form the four terrestrial planets: Mercury, Venus, Earth and Mars. A similar process formed the outer planets of the Solar System: Jupiter, Saturn, Uranus, and Neptune. Yet, they are different because icy materials such as frozen water, carbon dioxide and methane were also available. Consequently, these outer Jovian planets are much larger than the terrestrial planets. In addition these giant planets were able to enhance their atmosphere by capturing gas atoms moving more slowly due to the colder temperatures. Pluto, the ninth planet, is unlike its neighbours. It is a tiny rocky world just 2300 km in diameter (65% of the size of our own Moon). Up to now, its existence has baffled astronomers. Recent observations of these outer regions, however, have shown that there are other similar-sized objects, known collectively as transneptunian objects, in this area of the Solar System. It is possible that Pluto belongs to this group of objects. Each planet travels around the Sun in an elliptical orbit that is held in place by the gravitational attraction between the Sun and the planet. Some of the planets, including, of course, Earth, have moons orbiting them. Pluto has just one moon in orbit around it, while Jupiter has 63 moons known to be orbiting it. Kepler's three laws of planetary motion define the motion of the planets around the Sun, and the movement of moons around their parent planet. Teachers Notes Booklet 1: Introduction to the Universe Page 6 of 19 Distance Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto AU 0.387 0.723 1.000 1.524 5.203 9.539 19.182 30.058 39.440 106 km 57.9 108.2 149.6 227.9 778.3 1427.0 2869.6 4496.6 5900.1 Year Day 87.969d 224.701d 365.365d 686.980d 11.862y 29.457y 84.010y 164.793y 248.5y 58.65d 243.01dR 23.934h 24.623h 9.824h 10.233h 17.24hR 18.4h 6.39h d and y are multiples of Earth day and year. stands for retrograde, that is the spin of the planet is in the opposite direction to its orbital motion. * R Table 1.1: Distance and Orbital Parameters for the Planets Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Observational Parameters Mean Angular Mean Visual Diameter (") Magnitude 7.8 +0.0 25.2 -4.4 17.9 -2.0 46.8 -2.7 19.4 +0.7 3.9 +5.5 2.3 +7.8 0.1 +14.0 Moons 0 0 1 2 63 47 27 13 1 Physical Data Radius Mass Density Gravity 0.38 0.95 1.00 0.53 11.19 9.41 3.98 3.81 0.18 0.06 0.86 1.00 0.15 1323 752 64 54 0.01 0.98 0.95 1.00 0.71 0.24 0.13 0.24 0.32 0.36 0.37 0.90 1.00 0.38 2.69 1.19 0.93 1.22 0.03 *Limiting visual magnitude of human eye is around +6 *Physical Data is relative to the Earth: Radius – 6400 km; Mass – 6 x 1024 kg; Density - 5.5 kgm-3; Gravity – 9.81 ms-2 * No of moons correct at June 2005 Table 1.2: Observational Characteristics of the Planets BepiColombo is a joint mission with the Japanese Space Agency to explore Mercury. The mission consists of two orbital spacecraft: MMO – Mercury Magnetospheric Orbiter and MPO – Mercury Planetary Orbiter. Teachers Notes Booklet 1: Introduction to the Universe Page 7 of 19 Venus Express is heading for Venus to provide detailed analysis of its atmosphere. The mission is reusing technology already developed for the Mars Express and Rosetta missions. SMART-1 is a technology proving mission to test a new form of propulsion and miniaturisation technologies. This compact spacecraft's journey to the Moon took around 15 months and utilised an ion drive. Now in orbit around the Moon the spacecraft is providing detailed analysis of the surface. Mars Express, so called because of the rapid and streamlined development time, represents ESA's first visit to another planet in the Solar System. Borrowing technology from the failed Mars 96 mission and Rosetta, Mars Express is answering fundamental questions about the geology, atmosphere, surface environment, history of water and potential for life on Mars. A NASA/ESA/ASI mission to explore the Saturnian system. The ESA component consists largely of the Huygens probe, which entered the atmosphere of Saturn's largest moon, Titan, and descended under parachute down to the surface. Teachers Notes Booklet 1: Introduction to the Universe Page 8 of 19 1.3 Asteroids and Comets There were some materials left over from the solar nebula once the Sun and the planets had formed. Some of this debris remains in our Solar System in the form of asteroids and comets. Asteroids Asteroids, which are sometimes called minor planets, are rocky bodies mostly found in the planetary region between Mars and Jupiter. This region is known as the asteroid belt, and it stretches from about 250 million km to about 600 million km from the Sun. The largest known asteroid is Ceres with a diameter of roughly 1000 km. Only around a dozen are more than 250 km across. Over 100 000 asteroids larger than one kilometre in diameter are known to exist, with more being discovered all the time. We often hear of asteroids on the news, when near-Earth asteroids pass close enough to our planet to cause concern of a potential impact either now, or in the future. These near-Earth objects have highly elliptical orbits, which bring them into the inner Solar System, crossing the orbit of Mars and occasionally coming close to Earth. Comets Comets are often referred to as 'dirty snowballs', as they are made up of ice and dust. The ones we can see travel around the Sun in highly elliptical orbits taking from a few years to thousands of years to return to the inner Solar System. Typically comets are just a few kilometres across, which makes them very difficult to spot for most of their orbit. As they approach the Sun, however, solar radiation vaporizes the gases in the comet and the characteristic comet 'tail' is formed. The tail of a comet consists of two parts: a whiter part made of dust, which always points away from the Sun, and a blue part consisting of ionised gas. Comets are mainly found in two regions of the Solar System: the Kuiper belt, a region that extends from around the orbit of Pluto to about 500 AU from the Sun, and the Oort Cloud (from the Kuiper Belt to about 50 000 AU from the Sun). The Rosetta mission will track the comet 67 P/ChuryumovGerasimenko and deploy a lander onto its surface. On its 10year journey to rendezvous with the comet, the spacecraft will hopefully pass by at least one asteroid. Teachers Notes Booklet 1: Introduction to the Universe Page 9 of 19 Meteors Occasionally small rocks or dust particles enter the Earth's atmosphere. The dust particles and small rocks burn up in the atmosphere leaving behind brief trails in the sky witnessed as meteor showers. It is estimated that more than 200 million kg of meteoritic material is swept up by the Earth each year, with around 10% reaching the ground. Much of this material orbits the Sun in distinct streams, usually as debris from different comets. At various times throughout the year the Earth crosses these streams and for a few nights an observers can witness a meteor shower. Shower Quadrantids Lyrids Eta Aquarids Delta Aquarids Perseids Orionids Taurids Leonids Geminids Activity Dates Jan 1-6 April 16-25 April 19 – May 28 July 12 – Aug 19 July 17 – Aug 24 Oct 16-27 Oct 20 – Nov 30 Nov 14-21 Dec 7-17 Maximum Jan 3 April 22 May 5/6 July 29 Aug 12/13 Oct 21 Nov 5 Nov 17 Dec 14 Rate 60 15 35 20 75 25 10 15 75 Parent Object 2003 EH1A C/1861 GI Thatcher C 1P/Halley C pos. 96P/Macholz C 109P/Swift-Tuttle C 1P/Halley C 2P/Encke C 55P/Tempel-Tuttle C 3200 - Pantheon A Parent Object: A – Asteroid, C – Comet Rate – typical number per hour at maximum Table 1.3: Dates of Primary Meteor Showers Sometimes larger fragments survive their passage through the atmosphere and impact the surface, where they become known as meteorites. Most impacting fragments are tiny and cause little or no damage. Historically, however, there have been several major impacts, which may be responsible for changes in climate and the mass extinction of species. The image alongside shows the Barringer Meteor Crater in the United States. It was created around 50 000 years ago when a 50 m wide rock hit the ground at an estimated speed of 65 000 kilometres per hour. The resulting crater is 175 m deep, 1500 m wide and scattered debris in a 15 km radius. Figure 1.1: Barringer Meteor Crater (credit: NASA) Teachers Notes Booklet 1: Introduction to the Universe Page 10 of 19 1.4 Bodies of the Universe It is hard to comprehend the enormity of our Universe. Our Sun is only one of billions of stars in our galaxy, which is known as the Milky Way. But beyond the Milky Way, there are billions of other galaxies, too. Collectively, all these galaxies, along with the vast amount of space found in between them, are called the Universe. Solar System The Sun The star located at the centre of the Solar System, with a diameter of 1.39 million km and a visible surface temperature of 5780 K. Planets Nine planets orbit the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Moons There are now over 100 known moons in the orbit around the planets of the Solar System. Some, like Earth and Pluto, have just one companion while Jupiter has over 60. Comets Rocky-icy bodies in elliptical orbits travel through the Solar System developing a large tail of gas and dust in their orbit as they draw closer to the Sun. There are at least 150 periodic comets. Asteroids Thousands of rocky bodies, the largest being around 1000 km across, orbit the Sun. The majority are found between the orbits of Mars and Jupiter in a region known as the asteroid belt. In recent years observations have begun to probe the extent of another source of asteroid type objects (transneptunian objects) in the Kuiper Belt stretching 30 to maybe 100 AU. Teachers Notes Booklet 1: Introduction to the Universe Page 11 of 19 Our Galaxy Stars • Variables - stars whose brightness varies periodically • Binaries - 70% of all stars in our galaxy exist in multiple star systems • Neutron stars - a star with around 2 solar masses that is made up entirely from neutrons - remnants of a supernova explosion. • Pulsars - a rapidly spinning neutron star emitting pulses of radiation like a lighthouse • White dwarfs - a star with up to 1.44 solar mass that is made up entirely of electrons. • Novae - a star that undergoes a sudden increase in brightness by around 10 magnitudes and then declines over a period of months • Supernovae - a massive star that has exploded • Young hot blue-white stars • Old cool red star Star Clusters • Younger open, or galactic, clusters • Older globular clusters Nebulae • Planetary nebulae - remains of an old dying star • Emission - glows in the presence of UV light • Reflection - shines by reflected starlight • Absorption - dark, seen only as a silhouette • Supernova remnants • Gas Clouds and Interstellar Medium (ISM) Teachers Notes Booklet 1: Introduction to the Universe Page 12 of 19 Extragalactic Galaxies • Spiral • Barred spiral • Elliptical • Lenticular • Irregular Clusters and Superclusters of Galaxies Quasars Active Galactic Nuclei Gamma-Ray Burst Other Components Dark Matter Dark Energy Teachers Notes Booklet 1: Introduction to the Universe Page 13 of 19 1.5 Stellar Clusters & Constellations We are familiar with the constellations that we see regularly in the night sky - a distinctive pattern of stars. Although these stars may form shapes that are recognisable to us here on Earth, they do not usually have any real link to each other, as they are often at different distances from the Earth, and are in fact very far away from each other. Figure 1.2: View of Orion and Actual Distance to Stars Stellar clusters, on the other hand, are systems of stars that are held together by the gravity of their members. Eventually these clusters slowly evaporate. After a few billion years, the relatively loose collections of stars known as open clusters will no longer be held together by gravity and the cluster will stop existing. More highly compacted stellar clusters, known as globular clusters, which are typically about 15 billion years old, have not yet evaporated. Due to their relatively well-known distances, and the similarities that tend to exist among their stars, stellar clusters play an important role in astrophysics. Some of the nearest stellar clusters are visible with the naked eye. The most visible open clusters are the Pleiades and Hyades, both to be found in the constellation of Taurus. Name Pleiades Hyades Beehive M35 M47 NGC4755 M13 M4 ω Centauri 47 Tucanae Type Open Open Open Open Open Open Globular Globular Globular Globular RA 03h47 04h29 08h40 06h09 07h37 12h54 16h42 16h24 13h27 00h24 DEC +24°07 +16°30 +20°00 +24°20 -14°30 -60°20 +36°28 -26°32 -47°29 -72°05 North/South North North North North South South North South South South Table 1.4: Brightest Open and Globular Star Clusters Teachers Notes Booklet 1: Introduction to the Universe Page 14 of 19 1.6 Relative Distances to Objects A light year is the distance light travels through empty space in the course of one year. 1 light year = 9.461 x 1012 km = 5.878 x 1012 miles In order to comprehend the enormity of space, astronomers use a variety of methods to measure the distances between stars and between galaxies. Our own galaxy, the Milky Way, is around 120 000 light years across and the Sun occupies a position roughly 28 000 light years from the centre. Within the Milky Way, the nearest star to the Sun is Proxima Centauri, which is about 4.4 light years away. But most of our nearest stars are between 100 and 1000 light years away from Earth. From any given location on Earth it is possible to view around 7000 stars with the naked eye and countless more with a telescope. In all, our galaxy contains over 1 billion stars. The distance to stars in our galaxy is obtained using a technique called parallax. By identifying certain stellar properties it is then possible to calibrate a distance scale out to our galactic neighbours. The nearest galactic objects are the Magellanic Clouds. The Large Magellanic Cloud is 170 000 light years away, while the Small Magellanic Cloud is at a distance of 210 000 light years. The next nearest galaxy is Andromeda (M31 in the Messier catalogue), at a distance of 2.3 million light years. Galaxies are usually part of a larger group of galaxies. The group of galaxies that includes the Milky Way and Andromeda, plus several other smaller companion galaxies, is known as the Local Group. The other galaxies in the Local Group are between 80 000 to three million light years away from the Milky Way. The next nearest rich cluster of galaxies, the Virgo cluster, is around 60 million light years away. It is believed that the Milky Way-Andromeda cluster is part of an even bigger supercluster along with Virgo-Coma cluster. Teachers Notes Booklet 1: Introduction to the Universe Page 15 of 19 1.7 Stellar Motions Diurnal Effects During the course of one night, the constellations appear to move across the sky. Stars rise above the eastern horizon and set below the western horizon. The stars appear to rotate around one point in the sky. This optical effect occurs because the Earth itself is rotating about axis. Figure 1.3: The motion of star around the north celestial pole during the course of one evening. Annual Effects If you observe the night sky regularly over the course of one year, you will notice that the constellations appear to change their position slightly from one night to the next at any given time, only returning to their original positions once a year. This is due to the difference between a calendar day (24 hours) and a sidereal day (23 hours 56 minutes), or the time the Earth actually takes to spin once on its axis. Teachers Notes Booklet 1: Introduction to the Universe Page 16 of 19 Annual Parallax Annual Parallax is the difference between the position of a star observed from the Earth and by a hypothetical observer at the Sun. The effect is a tiny shift in the positions of relatively close stars against the background of distant stars. If the position of a nearby star is plotted during the course of a year it sweeps out an ellipse, called the parallactic ellipse, across the sky. This change in position is very small and requires high precision instruments to make the observation. Precession This effect, which can be observed for example with a spinning top, is caused by the gravitational pull from the Sun and Moon on the Earth's equatorial bulge. (Note - if the Earth were a perfect sphere precession would not occur.) Precession causes the Earth's rotation axis to sweep out a circle on the sky with an angular radius of 23° 27' (this value corresponds to the axial tilt of the Earth). The circle is traced out at the rate of 1° every 71.6 years, taking 25 800 years to complete a full circle. This means that the celestial pole, which currently points at the star Polaris, changes with time. Careful examination of Figure 1.3 (on the previous page) shows the Pole Star also leaving a star trail since it is ¾ of a degree away from the celestial pole. Teachers Notes Booklet 1: Introduction to the Universe Page 17 of 19 1.8 Other Materials This is booklet one in a series of six booklets currently available. The full range of titles is: Booklet 1 Introduction to the Universe Booklet 2 Stellar Radiation and Stellar Types Booklet 3 Stellar Distances Booklet 4 Cosmology Booklet 5 Stellar Processes and Evolution Booklet 6 Galaxies and the Expanding Universe Each booklet can be used to cover a topic on its own, or as part of a series. Booklets 5 and 6 expand on the material covered in the other booklets and there is, therefore, some overlap in content. All the booklets can be accessed via the ESA Science and Technology at: http://sci.esa.int/teachernotes For other educational resources visit the ESA Science and Technology Educational Support website at: http://sci.esa.int/education Teachers Notes Booklet 1: Introduction to the Universe Page 18 of 19 Teachers Notes Booklet 1: Introduction to the Universe Page 19 of 19