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EDEXCEL IGCSE PHYSICS 1 -6 Astronomy Edexcel IGCSE Physics pages 49 to 56 All content applies for Triple & Double Science July 22 nd 2011
Edexcel IGCSE Specification Section 1: Forces and motion d) Astronomy recall that the moon orbits the Earth and that some planets also have moons. understand gravitational field strength, g, and recall that it is different on other planets and the moon from that on the Earth. explain that gravitational force: – causes the planets to orbit the sun – causes the moon and artificial satellites to orbit the Earth – causes comets to orbit the sun use the relationship: orbital speed = (2× π × orbital radius) / time period v = (2× π × r) / T describe how the orbit of a comet differs from that of a planet recall that the solar system is part of the Milky Way galaxy: – describe a galaxy as a large collection of billions of stars – state that the universe is a large collection of billions of galaxies.
The Solar System consists of the Sun orbited by eight planets and their moons, some dwarf planets along with many asteroids and comets.
Planets A planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has cleared its neighbourhood of smaller objects around its orbit. Based on this, International Astronomical Union’s definition of 2006, there are only eight planets in orbit around the Sun. In order of distance from the Sun: Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Dwarf Planets A dwarf planet is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity. but has not cleared its neighbouring region of other similar bodies. As of 2011 there are five dwarf planets in the Solar System. Between Mars and Jupiter: Ceres Beyond Neptune: Pluto, Haumea, Makemake and Eris (the largest) Hubble image of Pluto and one of its moons (Charon)
Asteroids An asteroid is a celestial body orbiting the Sun that is not massive enough to be spherical as a result of its own gravity. Most asteroids are found between the orbits of Mars and Jupiter – a region called ‘The Asteroid Belt’. There about 750 000 asteroids larger than 1 km across. A few, called ‘Near Earth Asteroids’ can pass very close to the Earth. Asteroid Vesta – image taken on July 17 th 2011 by the Dawn spacecraft
Moons A moon orbits a planet. Planet Moons (2011) Mercury 0 Venus 0 Earth 1 Mars 2 Jupiter 64 Saturn 62 Uranus 27 Neptune 13 The Earth’s only natural satellite Note: A number of dwarf planets and asteroids also have moons, for example Pluto has three moons.
Time period (T ) This is the time taken for a planet to complete one orbit around the Sun. It increases with a planets distance from the Sun. Mercury 88 days Venus 225 days Earth 1 year Mars 2 years Jupiter 12 years Saturn 29 years Uranus 84 years Neptune 165 years
Gravitational attraction The force of gravity is responsible for the orbits of planets, moons, asteroids and comets. In 1687 Sir Isaac Newton stated that this gravitational force: - is always attractive - would double if either the mass of Sun or the planet was doubled - decreases by a factor of 4 as the distance between the Sun and a planet doubles.
Gravitational field strength (g) This is a way of measuring the strength of gravity. The gravitational field strength is equal to the gravitational force exerted per kilogram. Near the Earth’s surface, g = 10 N/kg In most cases gravitational field strength in N/kg is numerically equal to the acceleration due to gravity in m/s 2, hence they both use the same symbol ‘g’.
Gravitational field strength (g) varies from planet to planet. It is greatest near the most massive objects. Some examples of gravitational field strength: Location Earth N/kg 10 Location Jupiter N/kg 24 Moon 1. 6 Pluto 0. 7 Mars 3. 7 The Sun 270
Planet, Dwarf Planet or Moon Number of moons (2011) Average distance from the Sun (millions of km) Diameter (km) Time for one orbit (years) Average surface temperature (°C) Gravitation al field strength (N/kg) Mercury 0 58 4 700 0. 2 (88 days) + 350 4 Venus 0 108 12 100 0. 6 (225 days) + 470 9 Earth 1 150 (93 million miles) 12 700 `1. 0 + 15 10 Moon - 0. 38 (from the Earth) 3 400 0. 07 (27 days) - 50 1. 6 Mars 2 228 6 800 1. 9 - 30 4 Ceres 0 414 970 4. 6 - 100 0. 3 Jupiter 64 779 143 000 12 - 150 23 Saturn 62 1443 120 000 30 - 180 9 Uranus 27 2877 51 000 84 - 210 9 Neptune 13 4503 49 000 165 - 220 11 Pluto 3 5874 2 300 248 - 230 0. 7
Planetary orbits The orbits of the planets are slightly squashed circles (ellipses) with the Sun quite close to the centre. The Sun lies at a ‘focus’ of the ellipse
Planets move more quickly when they are closer to the Sun. faster slower The above diagram is exaggerated!
What would happen to an orbit without gravity As the red planet moves it is continually pulled by gravity towards the Sun. Gravity therefore causes the planet to move along a circular path – an orbit. If this gravity is removed the planet will continue to move along a straight line at a tangent to its original orbit.
Comets A comet is a body made of dust and ice that occupies a highly elongated orbit. When the comet passes close to the Sun some of the comet’s frozen gases evaporate. These form a long tail that shines in the sunlight. Comets are most visible and travel quickest when close to the Sun. Comets are approximately 1 -30 km in diameter.
Halley’s Comet This is perhaps the most famous comet. It returns to the inner Solar System every 75 to 76 years. It last appeared in 1986 and is due to return in 2061. It has been observed since at least 240 BC. In 1705 Edmund Halley correctly predicted its reappearance in 1758.
Choose appropriate words to fill in the gaps below: star The Solar System consists of a ______, the Sun, orbited by eight planets, a number of dwarf planets and millions of _______ comets asteroids and ____. orbit the Sun because of gravitational All of these bodies ______ moons and force. Gravity is also responsible for the orbits of _______ artificial satellites. ellipses but those of comets Most orbits are nearly circular _______ are highly elongated. Comets move ____ quickest when they are at their nearest to the Sun WORD SELECTION: quickest eight ellipses orbit star moons comets
Orbital speed (v) orbital speed = (2π x orbital radius) / time period v = (2π x r ) / T orbital speed in metres per second (m/s) orbital radius in metres (m) time period in seconds (s)
Question 1 Calculate the orbital speed of the Earth around the Sun. (Earth orbital radius = 150 million km) v = (2π x r ) / T = (2π x [150 000 km] ) / [1 year] but 1 year = (365 x 24 x 60) seconds = 31 536 000 s and 150 000 km = 150 000 000 metres v = (2π x [150 000 000] ) / [31 536 000] orbital speed = 29 900 m/s
Question 2 Calculate the orbital speed of the Moon around the Earth. (Moon orbital radius = 380 000 km; orbit time = 27. 3 days) v = (2π x r ) / T = (2π x [380 000 km] ) / [27. 3 days] but 27. 3 days = (27. 3 x 24 x 60) seconds = 2 359 000 s and 380 000 km = 380 000 metres v = (2π x [380 000] ) / [2 359 000] orbital speed = 1 012 m/s
Question 3 Calculate the orbital speed of the ISS (International Space Station) around the Earth. (ISS orbital height = 355 km; orbit time = 91 minutes; Earth radius = 6 378 km) The orbit radius of the ISS = (355 + 6 378) km = 6 733 km v = (2π x r ) / T = (2π x [6 733 km] ) / [91 minutes] but 91 minutes = (91 x 60) seconds = 5 460 s and 6 733 km = 6 733 000 metres v = (2π x [6 733 000] ) / [5 460] orbital speed = 7 748 m/s
Question 4 Calculate the orbital time of a satellite that has a speed of 3 075 m/s and height above the earth of 35 906 km. (Earth radius = 6 378 km) The orbit radius of the satellite = (35 576 + 6 378) km = 42 284 km v = (2π x r ) / T becomes: T = (2π x r ) / v = (2π x [42 284 km] ) / [3 075 m/s] but 42 284 km = 42 284 000 metres T = (2π x [41 954 000 ] ) / [3 075 ] orbital time = 86 400 seconds = 1440 minutes = 24 hours
Communication satellites These are usually placed in geostationary orbits so that they always stay above the same place on the Earth’s surface. VIEW FROM ABOVE THE NORTH POLE
Geostationary satellites must have orbits that: - take 24 hours to complete - circle in the same direction as the Earth’s spin - are above the equator - orbit at a height of about 36 000 km Uses of communication satellites include satellite TV and some weather satellites.
Choose appropriate words to fill in the gaps below: lower A satellite is a ____ mass object orbiting around a higher mass body. ____ slowly The larger the orbit of a satellite the more ____ it moves longer it takes to complete one orbit. and the ____ communications and have Geostationary satellites are used for _______ 24 hours. an orbital period of _____ monitoring _______ satellites normally use polar orbits. WORD SELECTION: monitoring higher longer lower communications 24 slowly
The Milky Way is the name of our galaxy. From Earth we can see our galaxy edge-on. In a very dark sky it appears like a ‘cloud’ across the sky resembling a strip of spilt milk. A very dark sky is required to see the Milky Way this clearly
Galaxies consist of billions of stars bound together by the force of gravity. There are thought to be at least 200 billion galaxies in our Universe each containing on average 2 billion stars. The Andromeda Galaxy The Sun’s position in the Milky Way
Types of galaxy Barred-Spiral – NGC 1300 Our galaxy is this type Spiral – The Whirlpool Galaxy Elliptical – M 32 Irregular – The Small Magellanic Cloud
Choose appropriate words to fill in the gaps below: Universe The ______ is made up of billions of galaxies which billions consist of _____ of stars bound to each other by the force of ______. gravity galaxy Sun The name of our _____ is The Milky Way. The ______ is located towards the outer edge of our galaxy. spiral The are different types of galaxy; ____, barred-spiral elliptical and irregular. The Milky Way is a ______ Andromeda galaxy. The _______ Galaxy is the nearest spiral galaxy to the Milky Way. WORD SELECTION: Andromeda galaxy spiral Sun Universe gravity barred-spiral billions
Online Simulations My Solar System - Ph. ET- Build your own system of heavenly bodies and watch the gravitational ballet. With this orbit simulator, you can set initial positions, velocities, and masses of 2, 3, or 4 bodies, and then see them orbit each other. Multiple planets - 7 stones Planet orbit info - Fendt Distances in Space - Powerpoint presentation by JAA Solar system quizes - How well do you know the solar system? This resource contains whiteboard activities to order and name the planets corrrectly as well as a palnet database - by e. Chalk Hidden Pairs Game on Planet Facts - by KT - Microsoft WORD Fifty-Fifty Game on Planets with Atmospheres - by KT Microsoft WORD Fifty-Fifty Game on Planets that are smaller than the Earth - by KT - Microsoft WORD Sequential Puzzle on Planet Order - by KT - Microsoft WORD Sequential Puzzle on Planet Size - by KT - Microsoft WORD Lunar Eclipse - flash demo Phases of the Moon - Freezeway. com Phases of the Moon - e. Chalk Seasons - Freezeway. com Gravity & Orbits - Ph. ET - Move the sun, earth, moon and space station to see how it affects their gravitational forces and orbital paths. Visualize the sizes and distances between different heavenly bodies, and turn off gravity to see what would happen without it! Projectile & Satellite Orbits - NTNU Newton's Cannon Demo - to show orbits occur - by Michael Fowler Kepler Motion - NTNU Kepler's 2 nd Law - Fendt Two & Three Body Orbits - 7 stones Orbits - Gravitation program BBC KS 3 Bitesize Revision: The Solar System Gravitational Forces Days & Nights Years & Seasons - includes an applet showing the tilt of the Earth The Moon Artificial space probes and satellites
Astronomy Notes questions from pages 49 to 56 1. 2. 3. 4. 5. 6. 7. Outline the structure of the Solar System and explain the difference between a planet and a moon. (see pages 49 to 50) Define what is meant by gravitational field strength and explain how it may differ throughout the Solar System. (see page 50) How is the orbit of a comet different from a planet? (see pages 51 and 52) (a) Give the equation for orbital speed. (b) Calculate the orbital speed of Mercury around the Sun. [Mercury orbital radius = 58 million km; orbital time = 88 days]. (see page 54) (a) What is the ‘Milky Way’? (b) What is a galaxy? (c) How many galaxies are there in the Universe? (see page 55) Answer the questions on page 56. Verify that you can do all of the items listed in the end of chapter checklist on page 56.