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The Universe and the Solar System 2 © Zanichelli editore 2015

The Solar System 3 © Zanichelli editore 2015

Stars and galaxies 4 The Universe is made up of stars: huge massive bodies that produce light in their core and are grouped together in galaxies. The Milky Way is the galaxy where our Solar System is located. Around the galaxies, there are often planets and satellites, which do not produce light. © Zanichelli editore 2015

The Solar System /1 5 The Solar System consists of the Sun and all the entities that feel its gravitational pull and move around it: planets, satellites, dwarf planets, asteroids and comets. Their distance from the Sun is expressed in astronomical units (AU): 1 AU = average distance Earth-Sun. © Zanichelli editore 2015

The Solar System /2 6 © Zanichelli editore 2015

The Sun is a star and produces light 7 The Sun produces light by thermonuclear fusion which takes place in its core. There, temperatures reach 15 million degrees and matter is in the plasma state. © Zanichelli editore 2015

Thermonuclear fusion reactions 8 During a thermonuclear fusion reaction, two or more atomic nuclei join, forming a more complex nucleus with a mass which is smaller than the sum of the initial masses. The lost mass is transformed into energy, in accordance with the equation E = mc 2. H H H H He + energy 4 nuclei of H (1 proton each) 1 nucleus of He (2 protons, 2 neutrons) © Zanichelli editore 2015

Light is energy 9 Light is a combination of electromagnetic radiation of different frequencies and wavelengths, that transport energy in the form of photons. Light moves at a speed of about km/s. © Zanichelli editore 2015

The planets around our Sun 10 © Zanichelli editore 2015

Terrestrial planets /1 11 In addition to Earth, the terrestrial planets are Mercury, Venus and Mars. They are small and rocky, but they have high densities. In fact they are mainly composed of metals and heavy elements such as silicon and iron. © Zanichelli editore 2015

Terrestrial planets /2 12 The surface of Mercury resembles the surface of the Moon: rugged, covered with dust and cratered due to the impact of meteorites. Mercury Radius (km)2439 Density (g/cm 3 )5.4 Period of rotation (days)59 Period of revolution (days)88 Average distance from the Sun (millions of km) 58 Number of satellites0 © Zanichelli editore 2015

Terrestrial planets /3 13 Venus is covered by thick clouds of sulfuric acid which reflect sunlight, making the planet extremely bright. It has volcanoes and impact craters. Venus Radius (km)6052 Density (g/cm 3 )5.2 Period of rotation (days)243 Period of revolution (days)255 Atmosphere componentCO 2 Average distance from the Sun (millions of km) 108 Number of satellites0 © Zanichelli editore 2015

Terrestrial planets /4 14 On Mars there are strong winds (up to 200 km/h) that can create violent sand storms and shape the landscape. Ancient riverbeds are also visible. Mars Radius (km)3396 Density (g/cm 3 )3.9 Period of rotation (days)24.4 Period of revolution (days)689 Atmosphere componentCO 2 Average distance from the Sun (millions of km) 229 Number of satellites2 © Zanichelli editore 2015

Jovian planets /1 15 The Jovian planets are Jupiter, Saturn, Uranus and Neptune. They are very large, do not have solid rocky crusts and display a remarkably thick atmosphere made of light gasses. © Zanichelli editore 2015

Jovian planets /2 16 Jupiter’s atmosphere is full of clouds in the form of equatorial stripes due to the planet’s high speed of rotation. Jupiter Radius (km)70850 Density (g/cm 3 )1.4 Period of rotation (hours)9.92 Period of revolution (years)12 Atmosphere componentH, He Average distance from the Sun (millions of km) 778 Number of satellites64 © Zanichelli editore 2015

Jovian planets /3 17 The system of concentric rings of Saturn has a range of over 200,000 km with a width of only 20 m. The rings are made of fragments of ice and solid matter. Saturn Radius (km)60000 Density (g/cm 3 )0.7 Period of rotation (hours)10.24 Period of revolution (years) 30 Atmosphere componentH, He Average distance from the Sun (millions of km) 1427 Number of satellites62 © Zanichelli editore 2015

Jovian planets /4 18 Uranus has a system of rings as well, although it is far less complex and bright when compared to Saturn. Uranus Radius (km)25400 Density (g/cm 3 )1.3 Period of rotation (hours)15.6 Period of revolution (years) 84 Atmosphere component H, He, methane Average distance from the Sun (millions of km) 2870 Number of satellites27 © Zanichelli editore 2015

Jovian planets /5 19 Neptune’s atmosphere is dense and filled with clouds and its composition is similar of that of Uranus, as it contains hydrogen, helium and methane. Neptune Radius (km)24300 Density (g/cm 3 )1.8 Period of rotation (hours)18.5 Period of revolution (years)165 Atmosphere component H, He, methane Average distance from the Sun (millions of km) 4497 Number of satellites13 © Zanichelli editore 2015

Minor bodies in the Solar System 20 The dwarf planets, like Pluto, have small masses and are spherical. Asteroids are rocky bodies with an irregular shape found mainly between Mars and Jupiter or at the edge of the Solar System. Comets come from the Oort Cloud and have a core of dust and ice which partially transforms into gas as it approaches the Sun. © Zanichelli editore 2015

Movements of the planets 21 © Zanichelli editore 2015

Rotation and the day 22 The motion of a planet around its axis is called rotation. The rotational period is a day. Each planet has a characteristic day-length which is independent of its distance from the Sun. Earth’s rotational period is approximately 24 hours. PlanetRotation Mercury59 days Venus243 days Earth24 hours Mars ~ 24 hours Jupiter10 hours Saturn10 h 40’ Uranus11 hours Neptune16 hours © Zanichelli editore 2015

Revolution and Kepler’s Laws /1 23 Kepler’s first law states that planets orbit the Sun in an ellipse, with the Sun at one focus. © Zanichelli editore 2015

Revolution and Kepler’s Laws /2 24 The speed of the planets varies between a maximum at perihelion and a minimum at aphelion. Each planet revolves around the Sun at a different average speed which decreases with increasing distance from the Sun. © Zanichelli editore 2015

How can we explain Kepler’s Laws? 25 The law of Universal Gravitation states that any two bodies attract with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. F g = G M 1 x M 2 d2d2 © Zanichelli editore 2015