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STAV & AIP VCE Physics Teachers' Conference 2005

Ideas for Effectively Teaching VCE Astronomy & Astrophysics
Robert Hollow CSIRO Australia Telescope National Facility Robert.Hollow@csiro.au http://outreach.atnf.csiro.au

Introduction
This workshop will provide you with some simple ideas, demonstrations and analogies that consolidate a conceptual grasp of the theory and skills in the Astronomy and Astrophysics detailed studies in the VCE. Despite the seeming lack of practical investigative work in these units there are many simple demonstrations and analogies that are effective in engaging and challenging students. They also lend themselves to the use of simulations and other software tools. Fortunately there are several excellent activities and packages freely available that can be used in the classroom and at home. This paper aims to provide teachers with a range of ideas and activities plus some useful data with which to cover some of the syllabus requirements. It is not intended to provide a detailed theoretical background on all the concepts as this is better covered in the various references but rather it aims to clarify some key teaching points and misconceptions about them. These are generally matched to the relevant syllabus points although some comments and ideas are applicable across several sections of the syllabus. In addition to the material specifically targeting the Victorian VCE Physics syllabus material from two additional papers has been incorporated into this paper. These were originally written for workshops given to NSW Physics teachers and cover the Astrophysics option and the cosmology section of The Cosmic Engine core topic. Two handy papers worth reading by Keith Burrows; Teaching Unit 2 with Astrophysics in 2004 and VCE Physics 11 ­ unit 2: ASTROPHYSICS DS from the 2004 VCE Physics Conference can both be obtained from http://www.vicphysics.org/teachers/preparingfor2004.html.

Syllabus Requirements for VCE Astronomy and Astrophysics
This paper uses the Physics Victorian Certificate of Education Study Design, Victorian Curriculum and Assessment Authority, 2003. The areas targeted in this paper relate to the Outcome 3.1: Astronomy in Unit 1 (pages 14-15) and Outcome 3.1 Astrophysics in Unit 2 (pages 20-21). For ease of reference they are included below:

Unit 1 Detailed Study 3.1: Astronomy
· · · · · · · · plot the positions of some observed celestial objects as a function of time of day and time of year on a standard grid, for example altitude-azimuth, right ascension-declination; describe the diurnal and annual motion of the stars and planets as seen from the Earth; describe telescopic observations of changes to celestial objects including planets; describe early geocentric models of the Universe and the epicycle orbits of the planets, including the model of Ptolemy; describe the Copernican heliocentric model of the solar system and its effect; relate Galileo's telescopic observations of the Moon, Sun, Jupiter and Venus to his heliocentric interpretation; describe the discovery by telescope of new celestial objects such as planets, asteroids, comets, nebulae, galaxies and black holes; assess telescopes, for example commonly available and space-based telescopes, according to their purpose, optical system (reflecting, refracting), mount (altazimuth, equatorial) and data collection system (optical, electronic);

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STAV & AIP VCE Physics Teachers' Conference 2005 · · · select appropriate data relevant to aspects of astronomy from a database; use information sources to assess risk in the use of astronomical equipment and making celestial observations; use safe and responsible practices in the use of astronomical equipment and making celestial observations.

Unit 2 Detailed Study 3.1: Astrophysics
· · · · · · · · · · · · compare two or more explanations of the nature and origin of the Universe; explain the steady state and Big Bang models of the Universe; analyse one or more computer simulations of aspects of the nature of the Universe; explain the link between the Doppler Effect and Hubble's observations; apply a qualitative understanding of methods used for measurements of the distances to stars and galaxies; explain the formation of galaxies, stars, and planets; describe the properties of stars: luminosity, radius and mass, temperature and spectral type; use the Hertzsprung-Russell diagram to describe types of stars, their evolution and death; explain fusion as the energy source of a star; compare the Milky Way galaxy to other galaxies; describe characteristics of the Sun as a typical star, including size, mass, energy output, colour and information obtained from the Sun's radiation spectrum; select appropriate data relevant to aspects of astrophysics from a database.
© Victorian Curriculum and Assessment Authority 2003

Given the time constraints of a one-hour workshop it is impossible and unwise to attempt to cover all of these dot points in one session. This paper, however, contains additional material that was not presented in the workshop session. It also provides an extensive range of links and resources. Required syllabus points are in red.

Concepts & Ideas for Unit 1 Detailed Study 3.1: Astronomy
This section provides some ideas, teaching strategies and material for the dot points in the Astronomy study area. It is not intended as a teaching program rather it highlights points to consider in addressing the sections within the detailed study. Many of the comments made are also relevant for the Astrophysics detailed study in Unit 2. · plot the positions of some observed celestial objects as a function of time of day and time of year on a standard grid, for example altitude-azimuth, right ascension-declination;

For this point it is useful to provide example maps of a region of the night sky for a specific time in two versions; one with an altitude-azimuth coordinate system (alt-az), the other using the right ascension-declination system. Students can determine the location of one or more identified stars using the two different coordinate systems. Having done this you could then issue a second pair of charts, this time for an hour later or the same time but at a different location but again showing much the same region of sky. Inspection by the students should lead them to realise that the alt-az coordinates are different but the Right Ascension, declination (RA-dec) ones have remained the same. This can then be used as a starting point for discussing why there are different coordinate systems and the relative advantages and disadvantages of each. You may also mention that other systems such as galactic coordinates also exist. An easy way to produce these sky charts is to use astronomical planetarium or charting software. There are many excellent packages available. Some commercial packages such as Starry Night (http://www.starrynight.com/) come in a variety of levels and prices and even have educational packages with worksheets for classes. Free alternatives that can be downloaded from the web include: 1. 2. 3. Cartes du Ciel: http://astrosurf.com/astropc/ (Win PCs) WinStars: http://www.winstars.net/english/index2.html Night Sky (for Macintosh computers): http://www.kaweah.com/Products/NightSky/

These programs can be used in a variety of ways with students but reward prior use and familiarity. The free packages are almost as versatile and powerful as the commercial ones. Most have add-on data sets if needed.

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STAV & AIP VCE Physics Teachers' Conference 2005 · Describe the diurnal and annual motion of the stars and planets as seen from the Earth;

Rather than just trying to describe these, students grasp the concept of an Earth rotating on its axis while revolving around the Sun better by using simulations such as those software packages already listed. In addition to these there are some excellent applets and simulations that specifically target this point. They include: 1. ClassAction Interactive Classroom Materials for Teaching Astronomy (http://astro.unl.edu/classaction/). These excellent modules were developed by a team at the University of Nebraska and can be run online or downloaded as zipped files to run on your own computer. They come with accompanying detailed teacher manuals. The modules include animations, questions (which you can modify) and background theory all presented in Flash windows. There are currently three modules; a. b. c. 2. Lunar Cycles Coordinates and Motions Stellar Parameters (includes sections and activities on photometry,

TKI ­ Day and Night: Views from the Southern Hemisphere (http://www.tki.org.nz/r/science/day_night/index_e.php) is an excellent resource produced by Te Kete Ipurangi; The Online Learning Centre in New Zealand. It is a set of Shockwave animations that can be downloaded to run on your own computer that develop from basic observations and principles the diurnal motion of the Sun and the phases of the Moon. Apart from its strong pedagogical framework it is particularly useful as it specifically shows how these appear to viewers in the southern hemisphere whereas as much of the other material available online and in publications shows it from a northern hemisphere perspective. The level is aimed below that of VCE students but it is probably worth using as a starting point anyway as most students still have misconceptions about at this stage.

If possible, encourage your students to actually go outside and observe the Sun, Moon and stars. Whilst you may be unable to incorporate a viewing night into your programming (though if you do you may find some useful hints in an article I wrote, available at: http://outreach.atnf.csiro.au/education/teachers/viewing/) they can still make their own observations. Careful questioning can help unearth their prior observations ­ does the Sun rise at the same point on their horizon every morning? Can they see the Moon during the day? Where is the Sun when the Moon is a new crescent? and so on. Students may know more than they think when probed. · Describe telescopic observations of changes to celestial objects including planets; Ideally you could have students observe a planet such as Venus or Mars or Saturn over time and note any changes (eg phase and size for Venus, size and ice caps for Mars, size and tilt or rings for Saturn). More realistically you rae unlikely to have time for repeated telescopic observations over an extended period of time. If you do have one observing session and Jupiter is visible try and have your students observe it at the start of the session. See if the Giant Red Spot is visible. Also note the relative positions of the four Galilean moons (not all of them may be visible). View it again after a few hours and see if they can detect any changes, the change in the positions of moons should be obvious. If you have a digital camera you may even try to photograph Jupiter and its moons through the telescope over several hours. Other objects that may exhibit changes through small telescopes or binoculars over successive nights are comets (if any are visible) and the Moon. With the Moon, concentrate on the terminator, the line between day and night. Some of the brighter variable stars may also be worth observing. The Astronomical Society of South Australia's Variable Star Group has a useful introductory page on observing at http://www.assa.org.au/sig/variables/faq.asp#startup as does the AAVSO at http://aavso.org/newobservers.shtml. If a prominent sunspot group is present on the Sun you could monitor its development and the Sun's rotation via projection through binoculars or a small telescope. Caution is needed here; do not allow students to directly view the sun! (see the ASA's recent factsheet on the Transit of Venus for one safe method of projection at http://www.astronomy.org.au/ngn/media/client/factsheet_15.pdf). If time is short or the weather poor you can always use a series of photos or images of planets or other objects. These are readily available from the web. Ideally try and locate those with time or date information available. The 2003 opposition of Mars generated a wealth of images by amateur astronomers through small telescopes (see http://www.celestron.com/mars/images.htm for examples). Another option is to view movies showing the rotation of a planet such as Jupiter or SOHO real-time movies of the Sun (http://sohowww.nascom.nasa.gov/data/realtime/mpeg/). If you want to show how far technology has developed and impress upon students the dynamic nature of distant stars you can even view time-lapse movies of images from the HST of the expanding ejected jet from the star XZ Tauri, at: http://hubblesite.org/newscenter/newsdesk/archive/releases/2000/32/ . · · Describe early geocentric models of the Universe and the epicycycle orbits of the planets, including the model of Ptolemy; and Describe the Copernican heliocentric model of the solar system and its effect;

These two points are links together here as the ideas and resources are much the same. Rather than try to describe just verbally or through static diagrams let students use simulations. Some of the planetarium-style programs mentioned previously can be used to generate or even view directly the path of a planet relative to the background celestial sphere,

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STAV & AIP VCE Physics Teachers' Conference 2005 thus introducing the concept of planets as "wanderers" and retrograde motion. Numerous applets an simulations exist that allow students to then explore the different models in more details. These include: 1. 2. 3. 4. 5. Ptolemy's Model: http://webpages.charter.net/middents/Ptolemy's%20Model.htm which shows the epicycle, equant and deferent centre for the relative motion of a planet around the Earth in a clean simple animation. Epicycle and deferent demo: http://www.phy.syr.edu/courses/java/demos/kennett/Epicycle/Epicycle.html is another useful applet with ability to change some parameters and display options. Webwalk one: Greek and Copernican Astronomy: http://www.d.umn.edu/~aroos/webwalkone.html provides a useful level of detail and some effective animated diagrams. Alternative Solar System: http://jove.geol.niu.edu/faculty/stoddard/JAVA/ptolemy.html allows you to compare the models of Ptolemy, Copernicus and Brahe with "Views from Above" and "Views from Earth". Ptolemaic Model Applet: http://solarsystem.colorado.edu/applets/Ptolemaic/extra.html also has links to applets of Kepler's laws. Philosophy of Science ­ Astronomy and the Scientific Revolution: http://www.anselm.edu/homepage/dbanach/ph31b.htm which includes useful material and links on Ptolemy, Copernicus, Galileo, Newtonian and others. Myths about the Copernican Revolution: http://www.math.nus.edu.sg/aslaksen/teaching/copernicus.html Starry Messenger: http://www.hps.cam.ac.uk/starry/ from the Whipple Museum of the History of Science at Cambridge University.

Other useful sites on the early history of astronomy include: 1.

2. 3.

There are many books relevant to this topic and some schools may even possess laboratory material from the old PSSC Physics course from the Dark Ages (well 1960 actually) that featured a strong historical perspective. It had a detailed set of photos showing the retrograde motion of Mars. Go hunting in your store room and you may be surprised! Discussion about the effect of the Copernican model could be wide ranging and provide an opportunity to talk about the birth of modern science, church/state relations and the concept of scientific models. · Relate Galileo's telescopic observations of the Moon, Sun, Jupiter and Venus to his heliocentric interpretation;

Some of the sites listed in the previous section are obviously useful here. One site however that is essential in dealing with Galileo is The Galileo Project (http://galileo.rice.edu/). It is an amazing resource that encompasses many aspects of his life, work and times. Follow the links in the Science section to obtain details about his telescopic observations, including his drawings. A handy exercise is to loan students a small cheap refracting telescope (the sort that can be purchased for under $20 from stores such as Australian Geographic) and see if they can obtain their own drawings of these objects and compare them with Galileo's versions. · Describe the discovery by telescope of new celestial objects such as planets, asteroids, comets, nebulae, galaxies and black holes;

An excellent paper summarising the value of the telescope and other tools in making new astronomical discoveries is The Growth of Astrophysical Understanding, in the November 2003 issue of Physics Today which fortunately is available online at: http://www.physicstoday.org/vol-56/iss-11/p38.html with diagrams. It is an update of his thought provoking book Cosmic Discovery: The Search, Scope and Heritage of Astronomy published in 1984 and regarded as a classic. For more specific detail on the history of the telescope you cannot go past Dr Fred Watson's Stargazer published in late 2004 by Allen & Unwin. It is immensely readable and would be a handy purchase for the school library. Fred is well known to listeners of ABC radio and is Astronomer in Charge of the Anglo-Australian Telescope in Siding Spring NSW. · Assess telescopes, for example commonly available and space-based telescopes, according to their purpose, optical system (reflecting, refracting), mount (altazimuth, equatorial) and data collection system (optical, electronic);

This point could develop into an extensive section but regardless of how far you take it there are a few key concepts worth imparting to your students even if they are not explicitly mentioned in the syllabus. More details on some of these points can be found at: http://outreach.atnf.csiro.au/education/senior/astrophysics/observingtop.html. 1. All telescopes are basically just "light buckets", that is they collect photons from distant sources. The larger the primary mirror or objective lens of the telescope, the more photons, just as the wider a bucket, the more rain it can collect. Professional telescopes do not have "eyepieces" ­ no one looks through them. All professional astronomy these days relies upon some form of electronic sensor/detector. The rapid uptake of charged-couple devices (CCDs) has even supplanted photography in professional observatories. Kodak, who previously made special emulsions for professional astronomy, has ceased production of them. Astronomers now utilise the whole of the electromagnetic spectrum. Different types of telescopes are optimised for different wavebands. As our atmosphere blocks some wavebands (UV, X-Ray, Gamma-ray and 4

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STAV & AIP VCE Physics Teachers' Conference 2005 some IR for instance) we need to place telescopes in space to observe at those wavebands. This becomes VERY expensive, the size and lifespan of such instruments is limited and there is little or no chance of fixing faults or installing equipment upgrades (other than with the HST prior to the 2003 grounding of the Shuttle fleet). 4. Weather: Even for those wavebands where we can observe from the ground (radio, visible and some IR) the atmosphere can have a degrading effect. Clouds and daylight are obvious factors for optical astronomy. Radio observations can normally be made day and night but at higher frequencies in the mm-wavebands humidity and rain can be factors. IR observations cannot be made through water vapour. In general, optical, IR and mmwave telescopes are best placed at high altitude. Light pollution has reduced the efficiency of some earlier generation professional optical observatories. Radio frequency interference (RFI) or radio pollution can affect radio telescopes. This too is an increasing problem with the spread of mobile phones, digital television and so on. Just as there are few optimum sites for optical telescopes, sites suitable for the next generation radio telescopes such as the SKA (Square Kilometre Array) are scarce. Fortunately Australia with its low population density has some ideal sites and is an active bidder for this international project. Reflector vs refractor: This battle was resolved over a century ago for professional optical telescopes. The largest refracting telescope made was the 40 inch Yerkes telescope near Chicago. Any refractor larger than this would absorb too many photons passing through its thick lens which would also sag under its own weight. Modern optical and IR telescopes use large primary mirrors. Currently the largest are in the 8 ­ 10m class either as single mirrors such as the 8.1m Gemini telescopes that Australia has a share in or the segmented hexagonal mirrors such those of the 10m Keck telescopes. A handy reference with details on and links to all the large optical telescopes in the world can be found at: http://nineplanets.org/bigeyes.html. Reflectors are far more efficient than refractors of equivalent size, cheaper to build and require shorter tube lengths for the same focal ratio which means that the dome or enclosure can be smaller. Telescope mounts ­ equatorial and alt-azimuth: Prior to the 1980s most large professional optical telescopes used equatorial mounts to compensate for the Earth's rotation when viewing celestial objects. Whilst easier to work out how to drive such mounts, they normally required large/heavy counterweights and resulted in large domes relative to the size of the telescope. It was only with the advent of more powerful and affordable computers that large telescopes could accurately track objects on alt-azimuth mounts. These mounts can be smaller and lighter than equatorial ones and the domes or enclosures much smaller than otherwise. One of the first modern alt-az telescopes was the 2.3m telescope at Siding Spring built by ANU in the early 1980s (http://msowww.anu.edu.au/observing/telescopes/2.3m.php). An interesting point is that the dome of the 3.9m AAT also at Siding Spring which has a horseshoe equatorial mount is about the same size as either of the Gemini domes even though these house 8.1m telescopes on alt-az mounts. Computer control has even impacted on amateur telescopes. Computer-controlled telescopes on alt-az mounts such as the Meade ETX125 can be purchased for about $1,500 and smaller models are even less. They are much easier and lighter for the occasional user to set up and use if they want to find and track objects than equatorial mounts, particularly for southern hemisphere users who lack an easily found pole star such as Polaris. Compensating for atmospheric distortion: Atmospheric turbulence degrades the actual resolution obtained by ground-based telescopes below their theoretical value. Until recently the best way to minimise this was to locate telescopes where such turbulence was low and average "seeing" of around 1 arc second could be obtained. Improvements in computer and materials technology together with the declassification of military research have spurred the development of adaptive optics for large telescopes. Such systems correct the effects of the atmosphere on the image so that a large ground-based telescope can match the resolution of the space-based HST and have greater sensitivity. For more information see http://outreach.atnf.csiro.au/education/senior/astrophysics/adaptive_optics.html. Large mirrors: Modern reflector mirrors are much thinner than those on earlier telescopes. The 8.1m Gemini mirrors are only 20cm thick for example. This makes them more thermally efficient so that they can cool quicker. As they are lighter the accompanying mount does not need to be as heavy. One drawback is that they flex and distort under their own weight as they point at different parts of the sky. This is corrected by active optics, generally a series of actuators that push back on the mirror through computer feedback to keep it in optimal shape.

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10. Detectors: Photoelectric detectors have revolutionised both professional and amateur astronomy. A 20cm backyard telescope equipped with a CCD costing a few thousand dollars is able to detect objects that once required long photographic exposures on the 200 inch Hale Telescope on Mt Palomar. Of course this also means that modern large professional telescopes are correspondingly more powerful too. The quantum efficiency of CCDs is much greater than that of the human eye or photographic film. More detailed discussion with illustrations can be found at: http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_photographicastro.html. Follow the link at the bottom of this page to the next page for details on photoelectric astronomy. One way to discuss CCDs with your students is to relate them to digital cameras. Most such cameras currently use CCDs though CMOS chips are becoming increasingly common (eg the entry level Canon digital SLRs).

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STAV & AIP VCE Physics Teachers' Conference 2005 It is worth pointing out that other types of detectors are used for wavebands such as radio, X-ray and gamma rays. · Select appropriate data relevant to aspects of astronomy from a database; One of the great strengths of astronomy as an educational resource for students is that they can readily access professional databases freely over the internet. A major international project at present is the creation of the Virtual Observatory which will allow professional researchers and others the ability to access and analyse astronomical data from observatories and instruments around the world. Whilst this is still in the developmental stage useful precursors such as SkyView already exist. Another point to emphasise it that is possible for students to make their own discoveries and do their own research investigations using online databases. More likely students will just use a database to access and obtain data which they can then analyse. A common example of this is to obtain a list of stellar properties that can be pulled into a spreadsheet such as Excel. Common problems students may then have to solve are to plot the stars on an HR diagram or create a histogram to determine relative numbers of different spectral classes or so on. There are some exceptional astronomical database resources designed for or at least suitable for educational use. Several are listed below. These are suitable for either the astronomy or the astrophysics design studies. · Nearest Stars (http://www.cosmobrain.com/cosmobrain/res/nearstar.html) is a handy list of the 50 nearest stars with several key properties such as parallax, spectral type and apparent and absolute magnitudes listed in table form. Follow the link to a second table listing the 50 Brightest Stars. NED ­ NASA/IPAC Extragalactic Database (http://nedwww.ipac.caltech.edu/) is the main online source of data on objects beyond our galaxy. Fully searchable, provides professional-grade data and references. NStars Database (http://nstars.arc.nasa.gov/index.cfm)is a NASA with details on 2.600 stars within 25 pc. Fully searchable, provides professional-grade data and references. SkyServer (http://skyserver.sdss.org/) is the educational home page for the massive Sloan Digital Sky Survey. It has a wealth of material for teachers and students at a variety of levels. There are some excellent tutorials and many projects offered, some of which are open-ended. This educational interface still provides access to the full database but has is easier for students to use. SkyView Virtual Observatory is an online facility generating images of any part of the sky at wavelengths in all regimes from Radio to Gamma-Ray. Use information sources to assess risk in the use of astronomical equipment and making celestial observations; Use safe and responsible practices in the use of astronomical equipment and making celestial observations.

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The key problem for the first of these points is locating the information sources. It may be worth starting with a brainstorming session to see which potential safety issues students identify. Believe it or not observational astronomy is not without risks. There have been injuries and fatalities among professional astronomers over the last few decades. Separating the list into amateur and professional observing may be useful. The table below lists some potential risks for each category. It is certainly not an exhaustive list. Amateur Observing · · · · · · Moving around in dark/tripping/hitting object Lack of sleep; observing at night then working during the day Insect bites at night Lifting heavy mounts and equipment Observing during cold nights Observing the sun using inadequate/unsafe equipment with resultant risk of eye damage · · Professional Observing Driving too and from observator