4. THE SOLAR SYSTEM 1.1. THE SUN. Exercises

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1 4. THE SOLAR SYSTEM 1.1. THE SUN The sun is the star located in the center of the solar system. The sun is a yellow star, since its superficial temperature is about C (although, the temperature can even reach 15 million degrees in the center). Although it is a medium star, the Sun is much bigger than the Earth. The mass of the Sun is times higher than the Earth s mass and its volume is over million times higher. Its rotation period is about days, because it depends on the area of the Sun. A point in the equator takes 25 days to complete a whole rotation, but it can take 38 days for regions around the poles. Exercises C) Describe the composition, temperature, and make a sketch of the Sun s atmosphere showing the locations of the core, radioactive zone, convective zone and photosphere Composition: The Sun is mainly composed by gases of hydrogen and helium (the hydrogen is burnt in a nuclear reaction to get helium). Temperature: the temperature depends on the area of the Sun. The temperature in the surface is about 5500 degrees, but the closer you are to the center, the higher the temperature is. In fact, it can reach 15 million degrees in the core.

2 Sun s atmosphere: - Photosphere: the deepest layer of the Sun - Convective zone: the layer below the photosphere where the light produced by nuclear reactions is transformed into heat. - Radioactive zone: the layer below the convective zone where the light produced by nuclear reactions travel to the surface. - Core: it the central area of the sun, where the nuclear reactions take place (where the atoms of hydrogen compress together to form helium) d) How is energy produced? What type of radiation does the Sun emit? The energy of the Sun is produced by nuclear reactions, which consist of joining two atoms of hydrogen to get helium. The sun emits different types of electromagnetic radiation, especially visible light, ultraviolet light and infrared light. e) You know the distance between the Earth and the Sun is 1 AU (do you remember how many kilometers are in one AU?). If you know that the light speed is km /s, how many minutes, does it take sunlight to reach the Earth? 1A.U. = 150 million km We know that the light travels km per second, so we can easily calculate the seconds that the light takes to do 150million km. We only have to do the division: X= / = 500 s But, we need to express the amount in minutes, so we need to divide by 60. So sunlight takes 8 minutes and 20 seconds to reach the Earth.

3 1.2. THE PLANETS A planet is a spherical celestial body, which moves around a star because of gravity and have cleared their orbit of other celestial bodies, that is, there are no more elements describing its same orbit. Planets don t have their own light. We can see them because of the sunlight. The four planets that are nearest to the Sun are Mercury, Venus, Earth and Mars. These are made of rock and metal. They are called the inner planets or the terrestrial planets because they are similar to the Earth. The other four planets, Jupiter, Saturn, Uranus and Neptune, are called the outer (or gas giant) planet because they are further from the Sun. Remember that planets do not give out light. We can only see them because they reflect the light from the Sun. Exercises a) What type of movements do planets have? Describe them The planets has two movements: - Rotation: it is the movement of the planet around its own axis. - Revolution/translation: it is the movement of the planet around the Sun, describing an elliptical orbit. b) Name the largest planet in the Solar System The largest planet is Jupiter c) Why are Uranus and Neptune the coldest planet? They are the coldest planets because they are the furthest from the Sun. d) Complete the chart about the planets of the solar system PLANET DISTANCE FROM THE SUN (millions km) DIAMETER (km) AVERAGE TEMPERATURE ( C) Mercury Range from -170 to 450 C SATELLITES PERIOD OF REVOLUTION PERODIO OF ROTATION 0 88 days 59 days Venus days 243 days Earth (Moon) 365,25 day 24 hours Mars Range from -123 to 36 C 2 (Deimos, 687 days 24h37min Phobos) Jupiter (Io,Europa, Callisto, ) days (11,9 years) 9h 55min

4 Saturn (Titan) Uranus (Titania) Neptune (Triton) days (29,5 years) days (84 years) days (165years) 10 h 30m 17 hours 16 hours e) Which planet Has the most satellites? Jupiter Is closest to the Sun? Mercury Supports life? The Earth Is the smallest in the Solar System? Mercury Spins on its axis in the opposite direction? Venus Has rings? Jupiter, Saturn, Uranus and Neptune. Actually, Saturn has got the most visible rings. f) Why is a day on Venus longer than its year? Because Venus takes more time in rotate around its own axis that in rotates around the Sun. Its rotation period is longer than its revolution period. g) Which planet Takes the longest to orbit the Sun? Neptune Is the fastest to orbit the Sun? Mercury Has the longest days? Venus Has the shortest days? Jupiter h) Why is Venus hotter than Mercury? Because Venus has atmosphere, that traps the heat inside (greenhouse effect). However, this effect doesn t exist in Mercury because of the absence of atmosphere Other celestial bodies: dwarf planets, comets and asteroids. Dwarf planets: the dwarf planets are round celestial bodies that orbits around the Sun. However, they cannot be considered planets, because of their small size and because they can t clear their orbits of other bodies (it can be other celestial bodies describing its same orbit). Examples: Pluto (after Neptune), Ceres (located in the Asteroid Belt) and Eris (located in Kuiper Belt) Comets: they are celestial bodies, made of rocks and ice, which describe a very eccentric orbit. They last from 5 to 300 years in complete their orbit. Asteroids: small celestial bodies made of rocks and ice. They are located in two areas called belts:

5 - Asteroid Belt: ring between the orbits of Mars and Jupiter where most of asteroids are located. - Kuiper Belt: area located beyond Neptune. Bigger asteroids are usually in this belt. EXERCISES a) What is a comet? Do you know any? A comet is a celestial body, made of rock and ice which orbits around the sun describing very eccentric orbits. b) Why can we rarely see a comet? We rarely see a comet because its orbit is so eccentric, so elongated, that it takes a lot of time to complete it. For this reason, it have to spend many years (even hundred years) to see a comet again. c) What is an asteroid? And a meteor (or shooting star)? An asteroid is a small celestial body, make of rock and ice, which are located in the Asteroid and Kuiper belts. A meteor or shooting star is an asteroid, which collide in the atmosphere of the Earth at high speed. Because of the friction with the atmosphere, its temperature increases, it burns up and it evaporates. d) What is a meteorite? A meteorite is similar than a meteor, that is an asteroid (or comet) which collides with the Earth s atmosphere, but it survives, it doesn t vaporize, so it collides with the surface of the Earth.