1. EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 1-6 Astronomy Edexcel IGCSE Physics pages 49 to 56 June 17 th 2011 All content applies for Triple & Double Science

2. Edexcel Specification Section 1: Forces and motion d) Astronomy understand gravitational field strength, g, and know that it is different on other planets and the moon from that on the Earth. explain that gravitational force: - causes moons to orbit planets - causes the planets to orbit the sun - causes the moon and artificial satellites to orbit the Earth - causes comets to orbit the sun describe the differences in the orbits of comets, moons and planets use the relationship: orbital speed = (2× π × orbital radius) / time period v = (2× π × r) / T understand that: - the universe is a large collection of billions of galaxies - a galaxy is a large collection of billions of stars - our solar system is in the Milky Way galaxy.

3. The Solar System The Solar System consists of the Sun orbited by eight planets and their moons, some dwarf planets along with many asteroids and comets.

4. 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 Neptune Uranus

5. 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)

6. 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 are about 750 000 asteroids larger than 1km 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

7. Moons A moon orbits a planet. PlanetMoons (2011) Mercury0 Venus0 Earth1 Mars2 Jupiter64 Saturn62 Uranus27 Neptune13 The Earth’s only natural satellite Note: A number of dwarf planets and asteroids also have moons, for example Pluto has three moons.

8. 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 Earth1 year Mars2 years Jupiter12 years Saturn29 years Neptune165 years Uranus 84 years Time period (T )

9. 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.

10. 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’.

11. Gravitational field strength (g) varies from planet to planet. It is greatest near the most massive objects. Some examples of gravitational field strength: LocationN/kgLocationN/kg Earth10Jupiter24 Moon1.6Pluto0.7 Mars3.7The Sun270

12. 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) Mercury0584 7000.2 (88 days) + 3504 Venus010812 1000.6 (225 days) + 4709 Earth1150 (93 million miles) 12 700`1.0+ 1510 Moon-0.38 (from the Earth) 3 4000.07 (27 days) - 501.6 Mars22286 8001.9- 304 Ceres04149704.6- 1000.3 Jupiter64779143 00012- 15023 Saturn621443120 00030- 1809 Uranus27287751 00084- 2109 Neptune13450349 000165- 22011 Pluto358742 300248- 2300.7

13. 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

14. Planets move more quickly when they are closer to the Sun. faster slower The above diagram is exaggerated!

15. 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.

16. 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 1-30km in diameter.

17. 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 240BC. In 1705 Edmund Halley correctly predicted its reappearance in 1758.

18. Choose appropriate words to fill in the gaps below: The Solar System consists of a ______, the Sun, orbited by _______ planets, a number of dwarf planets and millions of asteroids and ________. All of these bodies ______ the Sun because of gravitational force. Gravity is also responsible for the orbits of _______ and artificial satellites. Most orbits are nearly circular _______ but those of comets are highly elongated. Comets move ________ when they are at their nearest to the Sun quickesteightstarcometsellipses WORD SELECTION: orbitmoons quickest eight star comets ellipses orbit moons

19. 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)

20. 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 [150 000 000 km] ) / [1 year] but 1 year = (365 x 24 x 60 x 60) seconds = 31 536 000 s and 150 000 000 km = 150 000 000 000 metres v = (2π x [150 000 000 000] ) / [31 536 000] orbital speed = 29 900 m/s

21. 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 x 60) seconds = 2 359 000 s and 380 000 km = 380 000 000 metres v = (2π x [380 000 000] ) / [2 359 000] orbital speed = 1 012 m/s

22. 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

23. 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

24. 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

25. 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.

26. Choose appropriate words to fill in the gaps below: A satellite is a ________ mass object orbiting around a ________ mass body. The larger the orbit of a satellite the more ________ it moves and the ________ it takes to complete one orbit. Geostationary satellites are used for _____________ and have an orbital period of _____ hours. _____________ satellites normally use polar orbits. 24lowerlonger slowly communications WORD SELECTION: higher monitoring 24 lower longer slowly communications higher monitoring

27. The Milky Way 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

28. Galaxies 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 Sun’s position in the Milky WayThe Andromeda Galaxy

29. Types of galaxy Barred-Spiral – NGC 1300 Our galaxy is this type Spiral – The Whirlpool Galaxy Elliptical – M32 Irregular – The Small Magellanic Cloud

30. Choose appropriate words to fill in the gaps below: The ___________ is made up of billions of galaxies which consist of __________ of stars bound to each other by the force of ___________. The name of our _________ is The Milky Way. The ______ is located towards the outer edge of our galaxy. The are different types of galaxy; ________, barred-spiral, elliptical and irregular. The Milky Way is a ____________ galaxy. The _____________ Galaxy is the nearest spiral galaxy to the Milky Way. spiralgalaxy gravitybillions Sun barred-spiral WORD SELECTION: Universe Andromeda spiral galaxy gravity billions Sun barred-spiral Universe Andromeda

31. Online Simulations My Solar SystemMy Solar System - PhET- 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 planetsMultiple planets - 7stones Planet orbit infoPlanet orbit info - Fendt Distances in SpaceDistances in Space - Powerpoint presentation by JAA Solar system quizesSolar 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 eChalk Hidden Pairs Game on Planet Facts - by KT - Microsoft WORDPlanet Facts Fifty-Fifty Game on Planets with Atmospheres - by KT - Microsoft WORDPlanets with Atmospheres Fifty-Fifty Game on Planets that are smaller than the Earth - by KT - Microsoft WORDPlanets that are smaller than the Earth Sequential Puzzle on Planet Order - by KT - Microsoft WORDPlanet Order Sequential Puzzle on Planet Size - by KT - Microsoft WORDPlanet Size Lunar Eclipse Lunar Eclipse - flash demo Phases of the MoonPhases of the Moon - Freezeway.com Phases of the MoonPhases of the Moon - eChalk SeasonsSeasons - Freezeway.com Gravity & OrbitsGravity & Orbits - PhET - 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 OrbitsProjectile & Satellite Orbits - NTNU Newton's Cannon DemoNewton's Cannon Demo - to show how orbits occur - by Michael Fowler Michael Fowler Kepler MotionKepler Motion - NTNU Kepler's 2nd LawKepler's 2nd Law - Fendt Two & Three Body Orbits Two & Three Body Orbits - 7stones Orbits Orbits - Gravitation program BBC KS3 Bitesize Revision: The Solar System Gravitational Forces Days & Nights Years & SeasonsYears & Seasons - includes an applet showing the tilt of the Earth The Moon Artificial space probes and satellites

32. Astronomy Notes questions from pages 49 to 56 1.Outline the structure of the Solar System and explain the difference between a planet and a moon. (see pages 49 to 50) 2.Define what is meant by gravitational field strength and explain how it may differ throughout the Solar System. (see page 50) 3.How is the orbit of a comet different from a planet? (see pages 51 and 52) 4.(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) 5.(a) What is the ‘Milky Way’? (b) What is a galaxy? (c) How many galaxies are there in the Universe? (see page 55) 6.Answer the questions on page 56. 7.Verify that you can do all of the items listed in the end of chapter checklist on page 56.