INTRO - Astronomy 1F03 2010/11 Fall Term 2010/11 Classes:...

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Unformatted text preview: Astronomy 1F03 2010/11 Fall Term 2010/11 Classes: Tue,Wed,Fri 9:30-10:30 am Classes: Tue,Wed,Fri Instructor: Dr. James Wadsley Office: ABB 352 Teaching Assistants: Tara Parkin, Blair Cardigan-Smith, Tara Parkin Smith, Dennis Duffin, Jen Golding, Max Schirm Duffin Jen Schirm Assessment Assessment Term Work 40 % • ~ 6 Labs • ~ 2 Assignments • Outdoor observing/Planetarium Mid Term (Oct 20) 20 % Final Exam (Dec) 40 % Format Format Tuesday, Wednesday – Lectures Tuesday, Friday – Every 2nd week Labs Friday 6 Planetarium Shows (assigned seating) Outdoor observing starting Sept 20 Text Text Astronomy: A Beginner’s Guide to the Astronomy: Guide Universe, 5th Edition Universe, Chaisson & McMillan On-lline Resources On ine http://avenue.mcmaster.ca/ http://avenue.mcmaster.ca/ Sign on with your Mac-ID Planetarium Dates Planetarium Observing Alerts Observing Hand outs/Assignments Hand Why Astronomy? Why Historically: Ancient Motivations Historically: Modern Astronomy Modern This Course… This Ancient Astronomy Ancient Navigation – before compasses Seasons – before calendars Cultural/Religious Festivals Cultural/Religious before Christmas – Winter Solstice before Modern Astronomy Modern Beauty of Nature: Seeing and understanding understanding Toughest playground for Physics available available Origins of Life, the Universe and Everything Everything Course Goals Appreciation for the beauty of the universe universe A little bit of science that explains a lot about the universe about How astronomy research operates: The Scientific Method The Please! Ask questions Please! This course is for you – iit should satisfy t your curiosity about astronomy your If you have a question about astronomy or related physics – tell me after class tell and I’ll answer it in class and The Grand Scheme of Things The Space is big – and mostly empty Because space is big (and speeds are limited) astronomical things tends to happen slowly happen Comparative Sizes Comparative Earth Sun Relative Sizes: Sun 100x bigger Relative Actual Separation Actual Earth Earth Separation is 100x the size of the sun: 150,000,000 km At the speed of light: 300,000 km/s At The Earth-Sun trip takes 8 minutes The Sun Sun Light Year: How far light travels in one year travels The nearest stars to the sun are light years away sun The Milky Way galaxy consists of 100’s of consists of billions of stars and the most distant are 100,000 light years away from the sun the As we go larger, things take longer: longer: Hours to Billions Hours of years of Note the large empty gaps between object at every scale at The Sky The The Sky changes very slowly The Star don’t move on the sky on human Star move timescales: They appear in fixed patterns: Constellations patterns: Planets do appear to move Planets Orion 3 Dimensions projected onto our sky our The stars that make up Orion are at different distances different The Celestial Sphere Sphere The Earth’s The spin makes the sky appear to revolve around us around The Sky changes over the year The The Earth rotates on its axis but it also revolves around the sun the The 24 hour Solar day Solar determines when sun rises The Sidereal day measures Sidereal measures the absolute rotation of the earth compared to the stars: it is 3.9 minutes shorter it To a Star Axial Tilt Axial The Earth (and other planets) orbit in a flat plane around the sun sun The Earth’s spin axis is tilted The spin 23.5 degrees from vertical in this plane this This means the sun and planets move along a tilted circular line that rotates with the sky: The Ecliptic The The Zodiac: The Constellations over the year There are 88 There official official Constellations Constellations and 13 Of them intersect the Ecliptic Ecliptic The Seasons result from the tilt The Tilt causes the seasons because for half the year each hemisphere is tilted away (winter) or toward (summer) the sun the Equinoxes: Equal Night/Day Equinoxes: Summer Solstice: Longest day Summer Winter Solstice: Shortest day Winter Precession: Long Term Changes Changes Over 26,000 years the Earth’s axis Earth axis moves in a Complete circle Complete Polaris was not always the pole star star Astrology’s Astrology Zodiac is 2000 years off years Tropical zodiac (Western) (2010, UTC) (2010, UTC 20 March – 20 April 20 20 April – 21 May 20 21 May – 21 June 21 21 June – 22 July 21 22 July – 23 August 22 23 August – 23 September 23 23 September – 23 October 23 23 October – 22 November 23 n/a 22 November – 22 December 22 22 December – 20 January 22 20 January – 18 February 20 18 February – 20 March 18 Siderial Zodiac (Hindu) (Jyotisha) (2010, UTC) (2010, UTC 14 April – 7 May 14 14 May – 7 June 14 14 June – 7 July 14 14 July – 6 August 14 14 August – 7 September 14 13 September – 6 October 13 13 October – 7 November 13 13 November – 6 December 13 Name Aries Taurus Gemini Cancer Leo Virgo Libra Scorpius Ophiuchus Actual Location of Sun IAU constellation (2010) 19 April – 14 May 19 14 May – 21 June 14 21 June – 21 July 21 21 July – 11 August 21 11 August – 17 September 11 17 September – 31 October 17 31 October – 21 November 31 21 November – 30 November 21 30 November – 18 December 30 18 December – 21 January 18 21 January – 17 February 21 17 February – 13 March 17 13 March – 20 April 13 December – 6 January 13 13 January – 8 February 13 12 February – 7 March 12 15 March – 8 April 15 Sagittarius Capricornus Aquarius Pisces Source: Wikipedia 2010 The motion of the Moon The The Moon revolves around the Earth in a nearly circular orbit similar to the way the Earth goes around the Sun the The Moon is illuminated by the Sun: one side is always bright and one dark one The phases of the Moon occur because the fraction of the bright side visible to us changes as the Moon orbits visible The Moon The The Moon phases The take 29.5 days to complete to Eclipses Eclipses The Moon’s orbit is such that the Earth, Sun The orbit and Moon can line up now and then and A Lunar Eclipse occurs when the Earth Lunar occurs prevents sunlight from striking the Moon prevents A Solar Eclipse occurs when the Moon Solar occurs prevents sunlight from striking the Earth prevents Eclipses Eclipses By coincidence the Moon and the Sun appear to be a similar size on the sky (0.5 degrees) (0.5 The Sun is very large but very far away The The Moon is closer but much smaller The This means the Moon can just cover the Sun on the sky for a total solar eclipse Sun Lunar Eclipse Lunar Solar Eclipse Solar Partial Solar Eclipses Eclipses The Sun is not a point – part of it part can be blocked can Only a small region right behind the Moon gets a total Solar Eclipse Solar Annular Solar Eclipses Annular The Moon’s orbit is not The orbit circular – iits distance from ts the Earth varies the Sometimes it is further away during an eclipse, is smaller on the sky and doesn’t fully cover the sun: doesn fully an Annular Eclipse Annular No Eclipse every month: No Moon orbit is tilted 5 degrees Angular Angular Scale On the sky all you can measure directly is angular size is Moon ~ 0.5 degrees Moon Human Eye ~ 1 arc minute minute Hubble Space Telescope ~ 0.1 arc second second Distances to the objects in Space Space Objects in space appear as though projected onto a 2-dimensional surface projected dimensional (the celestial sphere) (the You need some extra information to determine how far away they are determine Distances to the objects in Space: Possibilities Space: Send a signal there and back: Only practical for the Moon and planets (e.g. Radar) Radar) Know how big it really is: Things look smaller far away (Standard Ruler) smaller Know how bright it really is: Things look fainter far away (Standard Candle) fainter Parallax Parallax Standard Candles Standard If you know how bright something is then you can tell how far away it is how Brightness decreases as the square of the distance: distance: F Flux (Watts m-2) Flux L Luminosity (Watts) Luminosity r radius (m) radius L F= 2 4π r Parallax Parallax Civil Engineers and Surveyors use triangulation to measure accurate positions and distances distances If one length is known angles can be used to determine other lengths determine Astronomers use a similar method – called Parallax called Parallax Parallax Parallax If you look at an object from two different locations its position relative to a background will change background Look at your finger with one eye at a time – what is behind your finger what changes for each eye changes Parallax Parallax The apparent position of a nearby object in space varies depending where you are on Earth you The stars are so far away they are do not noticeably appear to move appear Nearest star (proxima Centauri – Centauri 4 Light years, 0.8 arcseconds) Light arcseconds Parallax for Stars Parallax If you wait 6 months the Earth moves a long way: 300,000,000 km Thus even stars can appear to move on the sky sky Hipparcos satellite: Angles to 0.001 arcseconds, Angles arcseconds distances out to 100’s distances light years light Ancient Ancient Astronomy Ancient Astronomy – no telescopes but no no light pollution no Astronomy consisted of recording the sky with the naked eye, e.g. Greeks ranked stars by Magnitude e.g. Beliefs (thinking) considered more important than proof (actually looking) important Scientific Method Scientific The objective approach to events The No theory should be preferred except for its ability to explain events for A good theory should explain past events and predict future ones – Only a and predict Only testable scientific theory has value testable If the theory fails carefully performed tests, a new (or extended) theory is required required Example Example Theory The Earth is Round The Aristotle (384-322 B.C.) postulated that Aristotle 322 the Earth is round because its shadow on the moon is curved the This theory is tested at every lunar eclipse and has been demonstrated to be correct every time so far correct At the time it was fairly compelling – there wasn’t much else to go on Eratosthenes Eratosthenes Eratosthenes of Cyrene (276-195 B.C.) Eratosthenes Measured circumference of the earth using the angle to the sun on the same day of the year at two locations: Syene Syene (a deep well) and Alexandria (a post) The measurement relies on the theory The Eratosthenes (~200 BC) Absolute size of Earth Absolute 7.2 deg/ 360 deg = 7.2 5000 stadia/ Earth’s 5000 circumference circumference Earth’s circumference circumference = 250,000 stadia 250,000 = 40,000 km 40,000 ( error of 1% of true value!) value!) Occam’s Razor: Occam How to choose between theories After William of Ockham (1285-1349 AD) After 1349 philosopher and Franciscan Monk philosopher "Pluralitas non est ponenda sine non est sine neccesitate" or "plurality should not be neccesitate or posited without necessity.“ posited OR: Given multiple theories that explain all the observations, simpler explanations are best (more likely) are Aside: Aside: Modern Statistics and Risk Statistically, simpler explanations are more likely to be correct (assuming they do fit the observations) – Bayes Theorem Objective is approaching the truth, no consequences Objective In life, risk analysis indicates that unlikely but dangerous cases must be taken seriously dangerous For example: lightning – the chance of being hit is the small, consequences are large small, ...
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