Queensland University ofTechnology

School of Mathematics, Science and

Technology Education

February, 2003

The Changing SkyObservational exercises in astronomy

Acknowledgements

These resource materials have been written and compiled by:John Broadfoot Queensland University of Technology

Assoc Prof Keith Lucas Queensland University of Technology Dr Ian Ginns Queensland University of Technology

Illustrations and photographs:John BroadfootNASA (National Aeronautical Space Agency) USA

Layout and diagrams:John Broadfoot

Cover photograph:Saturn and rings (Voyager Mission, NASA)

Queensland University of Technology2003

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ContentsPage

1. Prior beliefs 1

Prior beliefs Activity 1.1 12. The Changing Stars 2

Finding North Activity 2.1 3Determining altitude and azimuth Activity 2.2 5

3. Recognising stars and constellations 6Star Patterns Activity 3.1 7Star Movement Activity 3.2 9Finding South Activity 3.3 12Observing the night sky Activity 3.4 13Astrophotography 14

4. Using binoculars and telescopes 16

Types of telescopes Activity 4.1 16Comparing telescopes Activity 4.2 17

5. The Changing Moon 18

Drawing Phases of the Moon Activity 5.1 20Recording Phases of the Moon Activity 5.2 21Movement of Sun, Earth and MoonActivity 5.3 22Model of Sun-Earth-Moon Activity 5.4 23

6. Our star - the Sun! 24

Projecting the suns image Activity 6.1 24Movement of the Sun Activity 6.2 26Keeping time Activity 6.3 28Modelling eclipses Activity 6.4 29

7. Our planets 31Observing the planets Activity 7.1 32Planetary conjunctions Activity 7.2 33Another conjunction Activity 7.3 34The scale of things! Activity 7.4 35The Terrestrials Activity 7.5 36The Jovians Activity 7.6 36The comets Activity 7.7 38

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EARTH AND SPACE

Module OutlineThis module contributes to the study of the Unit: MDB391 Earth and Space

Why study this module?Much prehistory and cultural traditions are associated with observations ofthe motion of celestial bodies and the stars. Some Pacific Islands cultureshave strong associations with the constellations using these to navigate acrossoceans and seas.ObjectivesAfter studying this module you should be able to: identify your own prior knowledge about the changing sky find cardinal directions using the sun or stars identify some major stars and constellations use star charts and models to observe changes in the night sky predict the movement of star patterns observe and record the changing shape and position of the moon recognise the phases of the moon predict changes to moon phases and the changing position of the

moon observe and predict the movement and the position of the sun and

planets be persistent and systematic in collecting data sketch observations accurately interpret tables of data create pictorial representations report on observations in an informed manner

ContentThe Changing Stars: Using coordinates to find direction and recordobservations; North; altitude and azimuthRecognising stars and constellationsObserving the night sky; star patterns and movement; finding South;The Changing MoonObserving and recording phases of the Moon; movement of Sun, Earth andMoon; Model of Sun-Earth-Moon systemOur star - the Sun: Projecting the suns image; movement of the Sun andseasons; eclipses.Our planets: Famous astronomers; observing planets; conjunctions

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Main ideas developedn Our Earth is part of a planetary system including the Moon and the

Sun.n Measurement of the positions of celestial objects may be made using

references to the Earth coordinates.n Direction may be found using a knowledge of celestial navigation.n Careful observation of the movement of stars, planets and the Sun

provides evidence for the relationships between the bodies within thesolar system and space.

n The tilt of the Earths axis and the annual revolution of the Earth aroundthe Sun causes seasons.

n Alignment of the Moon and Sun may cause lunar and solar eclipses.

Teaching and learning approachesThis module will be delivered through the use of support materials, a lectureprogram, laboratory and field based activities and a workshop/tutorialprogram. The practical component is strongly based on the application ofobservation and recording skills. Field studies are an integral part of theteaching program. Teaching and learning in this module is based on theconstructivist model of learning to ensure students have a thorough groundingand understanding of the concepts. Throughout the teaching of this modulethere will be a strong emphasis on the constructivist approach to learning.

Assessment strategiesThis module will be assessed in a way which provides students with theopportunity to demonstrate their knowledge of the application of conceptsand their ability to present an informed defensible opinion.Practical activities occur throughout the learning process. A field excursionforms part of the studeies and obeservational activities and field reports arepart of the assessment program.

References

BooksFreedman, R.A. and Kaufmann, W.J. (III), (2002). Universe (6th Edn).

Freeman.Seeds, M.A., (2001). Foundations of Astronomy (6th Edn). Brooks/

Cole.Seeds, M.A., (2002). Horizons: Exploring the Universe. Brooks/Cole.Burnham, R. (Ed.), (2002). Astronomy. Home Reference Library, Weldon

Owen Pty Ltd. Fog: San Francisco.

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WEB siteshttp://sci.esa.int/ This is the Home Page for the European Space Agencyand has many links to excellent sites for information and photographs. Itcontains many detailed topics on the solar system.http://www.nasa.gov/ This is the home page for the National Aeronauticaland Space Agency in the USA.http://spacescience.nasa.gov/education/index.htm This site containsmany excellent topics and ideas for educators. The site also gives access tothousands of photographs - Hubble Space Telecsope (HST), Photogalleryand Planets.Note: NASA and JPL images generally are not copyrighted. You may useNASA imagery, video and audio material for educational or informationalpurposes, including photo collections, textbooks, public exhibits and InternetWeb pages. See http://www.nasa.gov/gallery/photo/guideline.html andhttp://www.jpl.nasa.gov/images/policy/ for further details.http://teachspacescience.stsci.edu/cgi-bin/ssrtop.plex An excellent sitefor many teaching resources for astronomy.Software: //www.seds.org/billa/astrosoftware.html There are a numberof free and shareware programs listed on this site.

These eerie, dark pillar-like structures are actually columns of cool interstellarhydrogen gas and dust that are also incubators for new stars. Thepillars protrude from the interior wall of a dark molecular cloud likestalagmites from the floor of a cavern. They are part of the "EagleNebula" , a nearby star-forming region 6,500 light-years away in theconstellation Serpens.

Gas Pillars in M16 - Eagle Nebula.Pillars of creation in a star-formingregion, HST Photo No. STScI-PRC95-44a (NASA 1995).

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1. Prior beliefs

What do you know already?Many cultures throughout the world have many stories and beliefs relating to theorigins and movement of the sun, moon, planets and stars. Melanesian and Polynesiangroups are well known for using groups of stars to find their way across vaststretches of water. This is called navigation. Planting of staple crops and importantfestivals have also been associated with the sun, moon and appearance of stars atcertain times of the year. You may know some of these stories and cultural beliefs?

Activity 1.1 What do you know already?

Write down your own ideas using the questions as a guide.Discuss these ideas as a group and try to form a consensus (if possible).Report the groups beliefs to the whole class. Why did people rely on the changing appearance/position of the

moon and sun to plant crops? Which stars or constellation can be used for navigation? What do you know about the way the sun and moon moves and

the way stars move? In which direction would you look to watch the sunrise? How do you locate north? Where does the moon rise and set? How does the moons shape change? Is the moon always visible at night? Is the moon visible during

the day? Are tides related to the changing moon? Where do the stars appear to rise and set? What is the Southern Cross? How is astrology related to astronomy?

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nurarifzainudinSticky Notegraviti bulan lebih kuat berbanding matahari, sewaktu bulan penuh, tanah akan lebih lembab dan mudah diserap oleh tumbuhan

konsep masa

nurarifzainudinSticky Notemenggunakan kompas atau matahari

nurarifzainudinSticky Notegya, graviti bulan yang kuat menyebabkan air pasang

nurarifzainudinSticky NoteThe alignment of the Moon and the Sun determines the phase of the Moon.

nurarifzainudinSticky NoteThe moon always rises from the east and sets in the west. This shows that the earth is spinning in the opposite direction which is from west to east. The planets of the earth also move from east to west like the sun and the moon.

nurarifzainudinSticky Notetimur

nurarifzainudinSticky Notematahari dan buruj

nurarifzainudinSticky Notethe stars, sun, moon, and planets all seem to be moving east to west.

nurarifzainudinSticky Notetidak dan ya

nurarifzainudinSticky Noteburuj

nurarifzainudinSticky NoteAstronomy is a science that studies everything outside of the earth's atmosphere, such as planets, stars, asteroids, galaxies; and the properties and relationships of those celestial bodies. Astronomers base their studies on research and observation. Astrology on the other hand, is the belief that the positioning of the stars and planets affect the way events occur on earth.

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Research Prior beliefs

Use references to find out more about some of the old beliefs or your own priorbeliefs. You could interview friends or village elders to obtain a better insight intoother beliefs.

2. The Changing StarsThe night sky had many meanings to our ancestors. Ancient Babylonian, Greeksand Romans believed that the day and night skies contained many Gods andmythical creatures. Lives were controlled by beliefs in these ideas. Celtic tribesused astronomical events to predict important dates for festivals and agriculture.Some groups also used this knowledge to worship their gods and for paganrituals. Melanesian, Polynesian and Micronesian sailors found their way acrosslarge distances of water using the stars, sun, moon, planets and wave patterns. Infact we are now discovering that many ancients knew their way around the worldsoceans.

Ancient Babylonian and Greek beliefsIn olden times, in the Mediterranean area, the scholars of Babylon and Greeceused 12 Zodiac signs for the path of the animals. These zodiac signs appear atdifferent elevations at different times of the year. Only part of the zodiac band isvisible at any one time because the other signs are below our horizon. In midyear the band of zodiacal constellations is at a higher elevation. During thenight these signs move across the sky from east to west as shown in figure 2.1

Figure 2.1. The path of thezodiac signs on a mid yearevening

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Finding northThe direction of true north (towards the geographic north pole) can be found bywatching the changing length of a shadow during the middle of the day. When theSun passes the highest elevation in the sky it is said to transit the meridian, that is,the Sun crosses the line joining the north celestial to south celestial poles (figure 2.2).The highest position of the Sun will give the shortest shadow which lies along thenorth-south line.

Activity 2.1 Finding North

Hypothesis: What happens to the length of a shadow throughout the day?

You will need:

a piece of thick paper or cardboard (foolscap) a 75 to 100 mm nail with a flat head or another suitable pointed object a pair of compasses for drawing circles a protractor for measuring angles blue tack or gum

What to do:

1 Start your experiment soon after 11.00 a.m. and continue until about1.00 p.m. Times may be different for different times of the year anddaylight saving.

2 Find a flat place outside in the sun. A concrete path is ideal or use a flatboard. Make sure the paper or cardboard does not move or blow in thewind. Put heavy stones on it.

3 Mark a point near the centre of your paper. Standthe nail or stick upright on the paper on this mark(figure 2.3).

4 Mark where the shadow of the nail ends.

5 Take away the nail and use your compass toquickly draw a circle with a radius less than thelength of the shadow. Your circle should notreach the end of the shadow.

Figure 2.2. The path ofthe Sun as it transitsthe meridian.

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Figure 2.3. Stickis set up so that itis vertical.

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6 Put the nail back in exactly the same position. Make sure the nailshadow ends where it did before.

7 Leave the paper and nail in position for about 2 hours. Mark the pointon the circle when the tip of the shadow just touches the circle youdrew. You should also mark the position of the top of the nail shadowevery 15 minutes.

8 Watch carefully as the shadow lengthens again after local noon time.Mark the position when the top of the nails shadow again touches thecircle. Figure 2.4

9 Remove the nail. Join the centre of your circle to the two points wherethe shadows touched the circle. Becareful not to move the paper.

10 Use a protractor or your compass to divide the angle between theshadow lines into two equal parts. Draw this line right across yourcircle.

This line points true north and south.

Mark this line on the concrete or ground. Now remove your paper.

It is a good idea to paint the line or put some white paint on a post or objectthat is along this line. It can be used for other activities later on.

Questions

1 Describe the changes to the shadow direction and length as middayapproaches.

2 At what time is the shortest shadow seen?3 Draw a diagram to show how the shadow would change during a whole

day.

EastWest

Sun

Movement of the shadow end

Figure 2.4.Recording theposition of theshadow.

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Figure 2.5. This diagramshows the sun at azimuth270 (west) and altitude30

East90

West270

South180

North

0altitude

Locating and recording the position of objectsTo locate and record the changing positions of objects in the sky we need to be able tomeasure angles in a simple way. You carry with you one of the best and easy to usedevices for this It is called your hand.The activity that follows shows you how to estimate angles with your hand span.

Azimuth and altitudeWe need a way of measuring two things to find the position of an object. The first isthe direction or azimuth from true North which you found in the last activity. Thesecond is the angle above the ground. This is called the altitude.

Activity 2.2 Altitude and azimuth

This activity is best done outside in the middle of a field or sports oval.

What to do:

To find the size of your hand span, stand up and stretch your arm outstraight. Spread your fingers wide apart. Close one eye and line the outeredge of your thumb up with a distant tree or object. See what your littlefinger is lined up with. Move your thumb to this position. Keep doing thisand keep count of the number of times to go around a complete circle(360). Divide the number of hand spans into 360. This will give you thesize of your hand span.

Example: Number of hand spans in a circle = 20Therefore one hand span = 360/20

= 18 per hand span

The width across your knuckles (fist) will be approximately half of your hand span.To make it simple for you, most adults with average hands have a hand span of 20and a knuckle span of 10.You now have two useful ways to measure angles.

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Questions

1 Using your hand span estimate the altitude of a tree or building in thegrounds.

2 A student with a hand span of 18 measures the position of the moon earlyone evening. The measurements are five hand spans from north and twohand spans up from the horizon. What is the azimuth and altitude of themoon?

Extension: Measuring the height of a tree.

1 Using your handspan devise a way to estimate the height of a tree or heightof a building without using any other measuring devices.

2 How could you find the width across a river without crossing it and withoutany equipment?

3. Recognising stars and constellationsThis part will introduce you to some of the bright stars and constellations seen in thenight sky. Many of the constellations seen in books have names given to them byancient Babylonian and Greek scholars. You can see over 2500 stars on any clearnight. The stars we see are only the brighter ones. There are many more, in factsome 4 to 5 billion in our own galaxy which is called the Milky Way. The stars thatwe see with our eyes are in our galaxy. There are millions of other galaxies that weknow about. These are too far away for us to see the individual stars.Some stars are brighter than others. Astronomers label stars with a letter of theGreek alphabet to indicate relative brightness. These letters are similar to our owna, b, c, and so on. Alpha - , beta - , gamma - , and so on.

Research The Greek alphabet

1 Find a copy of the full Greek alphabet.

2 Some well known bright stars are Sirius, Regulus, Canopus, Achernar,Arcturus, Vega, and Antares. Locate these on star maps and list the formalnames.

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Star patternsMany stars have been grouped together into recognisable groups or patterns calledconstellations. Some of these patterns were made up by the ancients and you needa lot of imagination to see some of the mythical creatures. Most of the names of theconstellations are based on the ancient names however many southern star groupswere only seen during the explorations into the southern oceans. The SouthernCross (Crux) was named by these early seafarers. However we should alsorecognise that the southern constellations were also well known, by different namesand different legends, by southern civilisations. For example, the polynesians suchas the Tongans call the Southern Cross Toloa (wild duck).

Activity 3.1 Star patterns

Hypothesis: How do constellations appear to move during the night?This activity enables you to investigate the apparent effect of the earths rotation onsome constellations.

You will need: a piece of dark coloured cardboard sticky tape pin and nail another small piece of cardboard

What to do:1. Select one of the constellations in figure 3.1.

2. Roll your cardboard into a tube, at least 80 mm across, and tape it.

3. Obtain another piece of cardboard large enough to fit over the end ofthe tube. Use the nail or pin to make different sized holes to representdifferent brightness stars. (Large holes for bright stars!)

4. Tape your constellation card over the end of the tube. Make sure theside you pricked faces the inside of the tube. It is now ready for use.

5. Stand somewhere dark and look through the tube towards light.

Questions

1 What happens to the star pattern if you twist or rotate the tube?

2 Without twisting your tube, move it from east to west over the top of yourhead. What happens to the appearance of the constellation? Where is topand bottom?

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3 Relate this to what happens to the stars at night.

4 The constellation Orion rises with the three stars of the belt pointing east.Predict what you would observe when it sets? Sketch the changingorientation of Orion with reference to the cardinal points.

Figure 3.1.The viewer and star patterns formaking the star movement model

cardboard with pinholesto represent aconstellation

cardboard tube (frompaper towel or Gladwrap)

Figure 3.2. The constellation Orion as it appears when risingin the East at night. Compare this appearance of Orion to thatshown in the sketch above? (Photo: John Broadfoot)

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Star movementDuring the night the stars appear to move from east to west. If you look south,you will notice that some stars appear to move in circles. This happens slowlyduring the night.

Activity 3.2 Star movement

In this activity you will make a model of some stars that may have been used byPolynesian and Melanesian sailors to find their way across vast expanses of ocean.

You will need: One sheet of cardboard (A4) Scissors Circular star chart on page 10 Charcoal, black paint or texta pen Paper fastener

What to do:1. Place the circular star map (figure 3.3) over the piece of cardboard.

2. Mark the famous navigation stars by pushing through with yourpencil.

3. Mark the outline of the circle and its centre.

4. Now take away the star map and mark the stars, circle and centre onyour cardboard.

5. Cut out the circle and push a small hole through the centre.

6. Now use the remainder of your cardboard to mark and cut out therectangular shape (figure 3.4) given on the bottom of the next page.

7. Cut the slot along the line AB. Do not cut to the edges.

8. Push a hole through the major centre point nearest you.

9. Put your circle in the slot so that the two holes line up.

10. Pin the two pieces of cardboard together.

11. Colour the portion below the horizon black.

You now have a model of the stars around the South Celestial Pole as seen fromyour latitude. The pin or paper fastener is directly above the Earths South Pole. Ifyou turn your disk clockwise you will see what the stars do at night.The approximate latitudes for the major centres in Eastern Australia are Cairns (17S), Rockhampton (23 S), Brisbane (27.5 S), Sydney (34 S), Melbourne (38 S)and Hobart (43 S).

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Figure 3.3. Chart of the southern sky (from Rukl, A. (1979). The Amateur Astronomer.Prague: Octopus.)

A BHorizon line looking South

Cairns (17 S)

Figure 3.4. Approximate positions of the South Celestial Pole are shown for the majorcentres in Eastern Australia. Select the position to use for the pin.

Brisbane (27.5 S)

Sydney (34 S)

Rockhampton (23 S)

Melbourne (38 S)

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Questions

1 Turn the disk clockwise (). Describe what happens to the SouthernCross if you give the disk one complete turn.

2 What do the other bright stars appear to do?

You could think of your model as a steering wheel like that in a car. Just imaginesteering your boat across the ocean at night and using the stars as handles. Byseeing the regular rotation of these stars, the ancient navigators could keep the boatspointed in the direction they were headed.

3 Draw a line through the long axis of Crux (Southern Cross) to the pin atthe centre. Now draw another line from the pin to bisect the Pointers (and b Centaurus). You have now discovered a way to find south. We arenot sure if the olden time sailors used this method but it does work.

Figure 3.5. The appearance of the stars as they revolve around the South celestialpole. The SCP is marked on the photograph. This point is about 4 degrees above thehorizon. Can you pick out the Southern cross? At what latitude was the photographtaken?

Horizon looking South

SCP

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4 Rotate the disk and see if you can find other ways that the old worldsailors, Melanesians or Polynesians may have navigated.

5 See if you can locate some of these important stars at night. Use themodel to help you. There are some stars which go out of view for only ashort time. Rotate your model to see which stars do this. How could thesestars be useful in finding south?

6 See if there are any stars that do not set. These are circumpolar stars.What is maximum angle of such stars from the South Celestial Pole?

Finding southStars may be used to construct imaginary shapes just as the ancients did. Thediagram below shows the Southern Cross and the Pointers and Achernar. Thesestars rose and set in much the same position in ancient times as they do today.

Activity 3.3 Finding south

In this activity you will use the actual photograph (figure 3.6) that was taken of thesouthern part of the night sky. The Southern Cross and the Pointers are clearlyvisible above and between the trees. You will use this photograph to construct linesto locate the position of true South.

What to do:1. Draw a line along the long axis of the cross from - Crucis (left) to

- Crucis (right). Extend this line to the right out of the photograph.

2. Now join the two pointers. Bisect them with a line at right angles.Extend this line out of the photograph until it crosses the line drawn

Figure 3.6. A photograph showing the SouthernCross and the Pointers.

- crucis

- crucis

pointers

horizon

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before. The intersection of these two lines is the South Celestial Pole.

3. Now draw a vertical from the SCP to the horizon line. The point onthe horizon is True South. Mark this point on the diagram.

4. Now Refer to figure 3.3 again. Locate the stars Canopus and Pea-cock. Why would these stars have importance for celestial naviga-tion? Suggest a possible way of finding South with these stars.

5. Try to devise another way of finding South using the Southern Crossand the star Achernar.

Observing the night skyNaked eye viewing of the stars and constellations requires reliable and accurate starcharts. General charts as in many textbooks are hard to use because they dontgive the view from a local area. They are usually equatorial and based on celestialcoordinates which are hard to understand.Star charts produced using azimuth and altitude positions for stars are easier to usefrom a local position on the Earths surface. These can be produced by a number ofcomputer programs. The charts need to be based on the longitude and latitude ofarea in which you live.You will also need to remember how to use your hand and fist to estimate angles ofazimuth and altitude.

Activity 3.4 Observing the night sky

1. Use your unaided (naked) eye to locate all major stars and constella-tions visible at this time of the year. Refer to altitude-azimuth starcharts and use your hand and fist to estimate the positions.

2. Observe and sketch the position of one zodiacal and one circumpolarconstellation (e.g. Scorpio and Crux) at times one hour apart. De-scribe the differences in apparent positions and motion.

3. Use the South Celestial Pole chart (figure 3.3) to locate the position ofthe South Celestial Pole (SCP). Why is the SCP positioned at analtitude equal to the latitude of your location?

4. Use the model you made in Activity 3.2 to orient yourself to thecurrent position of the stars. Now try to identify the circumpolarstars. Observe these over a period of one hour and describe thechanges seen.

5. Draw labeled sketches to indicate how at least two constellations,other than Crux, could be used to find your way (that is to locateazimuth directions). Refer to figure Activity 3.3.

6. Locate any planets that are visible. Record there approximate posi-tions.

7. Use binoculars to observe and describe some major open clusters.

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AstrophotographyAstrophotography is an exciting way to record views of the celestial sky whichcannot easily be seen with the naked eye. Film can be far more sensitive to certainwavelengths of light than the eye. Expensive equipment is not necessary to obtainrewarding photographs, however, a good 35 mm SLR cameras with a B exposuresetting is necessary. In addition to the camera a relatively inexpensive cable releaseis required (about $10.00) for extended time exposures using the B setting on thecameras shutter speed. Cameras may also connected to telescopes using T-mounts, which are reasonably cheap (about $20).Due to the rotation of the earth, celestial objects appear to move from east to westbut this movement is not noticeable through a standard 50mm lens over 15 to 20seconds. However, in order to gain the most out of long exposures the telescopeand mount needs to be correctly aligned, that is, the polar axis of an equatorialmount must be exactly lined up with the south celestial pole. Due to the relativelyshort exposure times, alignment is not a major problem when photographing brightobjects such as the moon or venus, however, when photographing more diffuseobjects such as nebulae, long exposures and accurate guiding of the telescope andcamera is necessary. As a guide the longest exposure that will give sharp imageswithout a motor drive is shown below.

Effective Time for Time forfocal length critical work some blur(mm) (secs) (secs)

90- 180 2 8180- 350 1 4350- 700 1/2 2700-1500 1/4 11500-3000 1/8 1/23000-6000 1/15 1/46000 + 1/30 1/8

The following techniques and activities should provide a rewarding introduction toastrophotography.

Activity 3.5 Photographing stars(a) Photographing constellationsThe film and developer used will depend on the results wanted. Black and whitefilm of 400 to 3200 ISO (ASA) will give sharp pinpoints of light while the slowercolour films up to 400 ISO will show the colours of the stars. In general, the faster

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films are more grainy so some trading off is necessary in low light conditions, i.e. afaster film is needed to photograph celestial objects where light pollution is aproblem. Fainter objects also require faster film to reduce the time of exposure.Fine-grain developers should be used to develop your own black and white films.Mount the camera on a tripod and use a cable release. Set the camera to face thestars or group of stars to be photographed. Set the camera aperture at a small f-stop (lens aperture wide open) and the focus at infinity. A standard 50 mm lensallows up to a 30 second exposure without appreciable movement of the stars dueto the rotation of the earth.

If telephoto lenses are used, the exposure time reduces inversely to the focal lengthof the telephoto lens system. for example, a 300 mm telephoto lens reduces themaximum exposure time to 5 seconds. Obviously, this faster speed requires amuch faster film to capture the starlight. This is where some of the faster films suchas T-Max are advantageous. These photographs may be used to identify and namestars and constellations, compare the brightness of stars and estimate thetemperature of individual stars.

If a series of photographs of the same constellation are taken over several nights orweeks, many interesting phenomena may be recorded on film. Such phenomenainclude planets changing position along the ecliptic, comets and asteroids (manyhave been discovered in this way) and meteor trails.

(b) Photographing star trailsUse the same type of films as used for short exposures of stars. Mount the cameraon a tripod to face the direction to be photographed and use a cable release. Setthe camera to face the stars you are interested in. Expose, using B setting for anylength of time from a few minutes to several hours. Greater declinations (positionsclose to the South Celestial Pole) give less trailing therefore needing greaterexposure times. One problem with greater exposure times is that the film will oftenfail or become overexposed especially in areas of light pollution. Interesting effectscan be created by doubly exposing the film, by photographing star trails in moonlightand by including dimly lit scenery in the photograph.

Star trails are good for demonstrating several astronomical phenomena:

(i) The temperatures of stars may be determined when using colour print orslide film.

(ii) The length of a day may be calculated by multiplying the trail time by 3600divided by the angle of the arc the stars have traversed on the film.If the timeof the trail is carefully recorded,

(iii) The location of the South Celestial Pole (circular trails) and the CelestialEquator (straight line trails).

(iv) Meteor trails are often seen on star trail photographs.

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4. Using binoculars and telescopesIn viewing the night sky you should become very familiar with the main constellationsand bright stars which are visible from your local position. You should also be ableto locate the main cardinal points on your horizon. Initially your observations of thenight sky are based on the unaided or naked eye. Binoculars provide an excellentstepping stone to increase your visibility of celestial objects. The power should notbe too great as binoculars of high power (greater than about 7x) become difficult tosteady. Binoculars are excellent for viewing the moon, satellites of Jupiter, cometsand large field stars clusters, galaxies and nebulae.

4.1 Types of telescopes

(a) Sketch an example of the two major types of telescopes:Refracting telescopeReflecting telescope

(b) Show clearly the types of lenses and the paths of light rays througheach type of telescope.

(c) Record the focal length and f-ratio for each telescope (labels).(d) Compare the advantages and disadvantages of each type of

telescope.

Powers of a telescopeThere are three important powers to consider when using telescopes:

n magnificationn light gathering powern resolving power

The magnification of a telescope M = focal length of objectivefocal length of eyepiece

Light gathering power is proportional to the area of the objective.Resolving power (in seconds of arc) = 11.6

Diameter of objective (D)

A refracting telescope has the following label.

A reflecting telescope has the label:

f = 900 mmD = 75 mm

f = 1200 mmD = 200 mm

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4.2 Comparing telescopes

During your field nights you will use different types of telescopes. The main twotypes used will be refracting and reflecting.

(i) Draw labelled sketches of each type of telescope and note thephysical parameters on the labels on each.

(ii) Use the data to calculate the resolving power for each telescope.(iii)Compare the light gathering power of each telescope.(iii)If a 25 mm eyepiece is used for each telescope calculate the

magnification for each. Do the same for a 40 mm eyepiece.

F-ratioA fourth parameter is important when photographing celestial phenomena orobjects, the f-ratio. This is related to light gathering and in general the lower the f-ratio the less time needed to obtain an image on film or by digital means (CCD).

f-ratio = focal length of objectivediameter of objective

In 35 mm cameras this ratio can be varied by changing the size of the opening in thelens. This part of the camera is called the diaphragm.For example a camera with an f-ratio of 3.5 and a focal length of 50 mmwould have an objective diameter of 14.3 mm.

Exercise(a) A telescope has a focal length of 900 mm and an objective

diameter of 75 mm. Calculate the f-ratio.(b) A second telescope has a focal length of 1200 mm and an objective

diameter of 250 mm. Calculate the f-ratio.(c) How would these two telescopes compare when photographing

deep sky objects?

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5. The changing moonDoes the moon look the same every night? Is it in the same place at the same timeevery night? Does it always rise at the same point on the horizon? Does it alwaysset at the same time?This topic will introduce you to the movement of the Moon around the Earth. Youwill make first hand observations. These will be discussed in class. It is importantthat you make and record your own observations accurately. By observing themoon often you will begin to understand its changing appearance and position in thesky.

In early history the Moon was very important to many cultures. For example thePolynesian year was based on 13 cycles of the Moon as it changed from new moonto full moon and back to a new moon (one cycle). Did any other past cultures usethe moons changes as a calendar?To fully appreciate the apparent motion of the moon around the earth and Sun youneed to observe and record the changes in phases and positions over a full cycle.The following activities provide you with the opportunity to record the changes in amethodical way.After you complete activities 4.1 and 4.2 your results will be compiled andpresented as part of your portfolio of observations. A model for the motion of themoon should be developed.

Figure 4.1. TheFull Moon as seenfrom Earth

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Drawing phases of the MoonIt is very important to draw accurate representations of the moon as it changes fromday to day. You need to record the position in the sky, the time and the shapeduring your observations from the New Moon for two to three weeks. In this firstactivity you will learn to record the moons shape as accurately as possible. Thisactivity will be done in conjunction with activity 4.2 in which you will record thetime, position and shape of the moon.

The moon has no atmosphere. This results in a cleardemarcation between the lit and unlit portions of itssurface (figure 4.2). The line so formed is called theterminator. The area enclosed by the terminator (anarc of an ellipse) and the nearer edge of the moon (anarc of a circle) is called a lune or simply a crescent.During a synodic month, about 29 days, the moonpasses through its complete cycle of phases. Theorientations of the lune vary in a complex fashion dueto the varying setting azimuths and path of the moonwith respect to the sun and earth. The followingchanges can be seen when the moon is in the west:

Figure 4.2. The Moons surfaceis heavily cratered. This isbecause the moon has noatmosphere to protect it frommeteorites. The absence of anatmosphere is clearly seen inthe top right of the photograph.There is an abrupt contrastbetween the surface and space.

Terminator

LuneHorn

New Moon Full Moon Old Moonevening daytime

Waxing Moon Waning Moon

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Activity 5.1 Drawing phases of the moon

This exercise enables you to draw the terminator for any age moon. The lune, oncedrawn, is shaded appropriately to represent the phase of the moon. That is, for acrescent moon, the lune is left white while the remainder of the moon is shadedblack and for a gibbous moon the lune or crescent is shaded black. The linebetween the lit and unlit parts of the moon should always begin and end on thediameter of the moon as shown in figure 4.3.1. Use your compass to draw a circle on a blank sheet of A4 paper. Use

a radius of 10 cm.

2. Mark the diameter of the circle.

3. Now use the lune widths as given in the table 4.1 on to sketch andshade 3, 7, 13, 22, 25 and 28 day old moons. All of the circles shouldhave a 10cm radius.

4. When you have completed your sketches, clearly label the phase oneach.

5. Draw an Earth-Moon-Sun diagram to show the position of the moonat each of these phases.

Terminator

LuneHorn

Diameter

Lune width

Figure 4.3 Terminology used todescribe the moons dimensions.

Table 4.1. Lune widths related to the age of the moonAge of moon Lune width

(days) (cm)1 0.22 0.93 2.04 3.45 5.16 7.17 9.28 8.79 6.610 4.711 3.012 1.713 0.714 0.115 0.0

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5. Draw an Earth-Moon-Sun diagram to show the position of the moon at eachof these phases.

Observing phases of the moonWhich way does the moon move?Where does the Moon appear to rise and set?The answers to these questions only become a reality through first hand observation.In this activity you make observations of the moon for about three weeks beginningat a new moon. Your observations must be submitted as part of your field report.

Activity 5.2 Observing phases of the moon

Observe the moon at about 7 p.m. each evening. Use your hand span to estimatethe position, azimuth and altitude of the moon from the horizon. You should havepreviously established the cardinal points (NESW) at your locality and themagnitude of your hand span.Record your observations in an appropriate manner to clearly show your data andobservations. For each observation include a sketch showing clearly the relativeposition of the moon to the horizon and the cardinal points. Binoculars may be usedto assist in recognising major features on the moons surface. Use a detailed surfacemap of the moon to identify major features.Questions1 How does the moon change while you have observed it?

2 Identify the phases and write these in your table of observations.

3 On what date was the moon full?

4 When the moon was full, about what time did it rise? Where did it rise?

5 How does the moons position change each day?

$

Figure 4.4. Phases of the moon aredue to the direction of sunlight asseen from where we stand on theEarths surface. Even the Earthshows phases when viewed fromouter space.

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Activity 5.3 Movement of Sun, earth and moon

This activity is a role play. Organise into groups representing SUN, MOON andEARTH. Arrange your groups outside the classroom as shown below. This activityis valuable in that you will quickly understand the nature of lunar phases.

What to do:1. You only need yourselves and a large ball. Colour half of the ball

white using water paint, whitewash or chalk.

2. SUN group Stand, in the middle, in a small circle with backs toeach other. You are the SUN.

3. EARTH groupA group of four students stands in a similar wayabout 10 metres away from the SUN.

4. MOON group One student holds the ball that is half white abovehis or her head and about 3 metres from the EARTH. The white sidemust always face the SUN. The student should face the SUN with thewhite side of the ball also facing the SUN.

5. The MOON now slowly walks around the EARTH making surethe white side of the ball always faces the SUN.

6. Groups should interchange roles to enable everyone to gain a differentperspective of the positions of the moon, sun and earth.

Figure 4.5. How you should be arranged in your groups

MoonEarth

Sun10 metres

3 metres

FF

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Questions1 What does the SUN group notice about the appearance of the MOON?2 What does each of the EARTH group notice about the appearance of the

MOON? Each person (EARTH only) should make a sketch of the whitepart of the ball.

3 The four students in the EARTH group are to slowly turn and notice thedifferent appearance of the white part of the ball.

4 Take turns at being the EARTH so that all students see the changes to themoon.

After doing this activity you should by now realise that the moon does changeits appearance as it moves around the earth.

Activity 5.4 Sun-earth-moon model

In this activity you are to build a model to represent the Moon orbiting the Sun andthe Earth orbiting the Sun. After observing and recording the apparent motion ofthe Sun and Moon you should now be able to use basic materials to explain some oflunar changes you observed.

You will need: One tennis ball (Earth), one ping pong ball or similar sized object (Moon) A large ball about the size of a volleyball or soccer ball (Sun), two sticks

and a one metre length of string.

What to do:1. Using your string and two sticks mark out a circle of 1 metre radius

on the ground.

2. Place the large ball at the position of the centre to represent the Sun.

3. Place the smaller ball on the circle. This will represent the Earth.

4. Now place the ping pong ball about 30 cm from the Earth.

5. You now have a model for the Sun-Earth-Moon. The Earth and theMoon may be moved to represent different times of the year anddifferent phases of the moon.

Investigate each of the following using the model1 Place the moon in positions to represent the phases:

new first quarter full last quarter

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2 Imagine that the earth turns anticlockwise and the moon orbits the earthanticlockwise, use your model to explain why the moon changes shapeeach lunar month.

3 What might happen when the moon is between the sun and earth?

4 What might happen when the earth is between the sun and moon?

5 Use your model to explain why the first quarter moon doesnt rise untilabout midnight.

6 Draw sketches of the model positions for the questions above.

6. Our star - the Sun!In section two of these notes you were introduced to the Suns apparent movementwhile finding true north. The following activities enable you to observe and recordthe Suns motion in more detail and apply your findings to the construction of asundial and to explain the occurrence of eclipses.

Projecting the Suns imageYou must take great care not to look at the Sun because the intensity of the light candamage your eyes (retina). This is because the lens of your eye acts as a magnifyingglass and concentrates the light energy onto a small spot which can become very hotand burn the tissues.

Activity 6.1 Projecting the Suns image

1. Find a shady tree and observe the shapes of the sunlight on theground.

2. What regular shape do you observe for some of the images? Explain,using a sketch, what is happening .

3. Now obtain a convex lens and a sheet of white cardboard. Place thecardboard on the ground and move the lens up and down until youget an image on the paper. Look carefully at the image. Describe andsketch the image. Do you see any features on the surface of theimage? What might these be?

4. This experiment can be extended by placing a dark filter between thesun and the lens. How might this change the experiment and theobservations?

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5. The suns image may also be projected using a pinhole in a card(figure 5.1). Obtain a piece of cardboard and pierce it with a pin.Now hold you pinhole between the sun and another whit sheet ofcardboard. Move it up and down until you see an image. Describethe image and sketch hoe you think it formed.

6. Finally you may make a pinhole camera to project the image of thesun onto an opaque surface such as acetate or tracing paper. Designsuch an instrument and report on its success or otherwise. You willfind excellent ideas and designs on the web.

Figure 6.1. Projecting the imageof the Sun using a pinhole andwhite cardboard for a screen.This is the safest way to look atthe Sun.

Figure 6.2. A telescopephotograph of the Sun. Thesurface shows dark spots.These are called sun spots.They are areas that are coolerthan the surrounding area.(Photograph: John Broadfoot)

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Movement of the SunIn this activity you need to observe the suns rising or setting positions forapproximately four weeks. Observations need only be made every 2 to 3 days asthe Sun does appear to move slowly.

Activity 6.2 Movement of the Sun

Make a series of observations of the exact rising or setting of the sun and record thecardinal positions and the times of observation. Present these observations as aseries of accurate sketches with your portfolio for assessment.Questions1 Describe the changes in the cardinal rising or setting positions of the

Sun.2 Predict where the sun would rise on June 22. Explain your answer.3 Predict where the sun would rise and set on about the 22 December.4 Prepare a model or a sketch to illustrate clearly how the Suns motion

changes throughout a year. Label the model or sketch clearly.5 How do the changes throughout the year affect the shadows of vertical

objects as seen in Brisbane.6 Design a method to use a knowledge of the Suns motion to find your

longitude at any place on the earths surface.

FF

Figure 5.3. Relationship between the orbits of the Earth and Moon around the Sun.When the Moon crosses a node an eclipse of the moon or sun may occur.

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Keeping timeTime keeping depends on a knowledge of the Earths motion around the sun or,from an earth-centred view, the apparent motion of the sun about the earth. It isnow known that the Earth has an inclined axis (2327) on which it rotates givingday and night in a cycle of approximately 24 hours (23h56m04.1s to be moreaccurate). This period of rotation is called a sidereal day and is the time taken forthe same place on Earth to complete one rotation with respect to a point in space.A solar day varies slightly and is the time taken for the same place on the earthssurface to complete one rotation with respect to the Sun.Keeping time is a complex business due to the complex movement of the eartharound the sun. The major factors affecting our time are due to the elliptical orbit ofthe Earth around the Sun. The Earth-Sun distance varies during the year and thevelocity of the Earth varies being greater at perigee (closest to Sun) than apogee(furthest from the Sun). These small variations affect time!Sun dials were used in Egyptian times and can still be found in use as ornamentsrather than exact timekeepers. Why? Sundials can be quite accurate howevercorrections need to be made for every different place on Earth. Imagine howunwieldy this would become if everyone had their own local time from sundials. Forthese reasons the invention of the chronometer soon saw sundials become a thingof the past. Following the rapid development of clocks the world adopted aUniversal Time (UT) system based on Greenwich (near London). Universal Time isalso known as Greenwich Mean Time. Therefore if you see time expressed as UTor GMT this is the time at 0 longitude.

How do you find the time in other places?We know that the Earth rotates once on its axis every 24 hours therefore a full circleof 360 must pass in 24 hours. This means that the Earth rotates at 15 per hour or1 degree every 4 minutes. This knowledge can be applied to find the Local MeanTime at any location if the GMT and the longitude is known.For example, Brisbane is 153.02 east of Greenwich (0). This means thatBrisbanes time is 153.02 x 4 minutes ahead of Greenwich. That is 10h12m ahead!Now it is not very useful to have every town or city calculate their own Local MeanTime therefore a system of time zones was created to unify the time for variouslongitudinal zones around the world. The eastern States of Australia have adoptedthe Zone Time based on the 150 meridian or longitude. This time zone is knownas the Australian Eastern Standard Time (AEST) which is 10 hours ahead ofGMT. Eastern Summer Time is a variation of the AEST applied by someAustralian States for daylight saving! The clocks are advanced one hour duringsummer. No daylight is saved at all!In activity 2.1 you located True North by observing the shadow of a vertical stick.The time at which the shadow was shortest corresponded to the time (Local Noon)at which the Sun was highest in the sky. The Sun was seen to transit (pass) the localmeridian (longitude).

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Activity 6.3 Keeping time

Time Zones1. Review Activity 2.1 Finding North and repeat this experiment by

setting your watch or a clock to the GMT and using this time for yourexperiment.

2. Note the exact GMT and AEST at which the Sun transits the merid-ian.

Questions1 What time (GMT) did the sun actually transit your meridian?2 Calculate the difference in longitude between Greenwich and your

location using the GMT.3 What is your calculated longitude East of Greenwich?4 How does your answer compare to the actual value of 153.02 for

Brisbane?5 Now compare the recorded AEST to the time of transit. Was it before or

after noon? Explain any differences in terms of your knowledge aboutkeeping time.

6 Draw a labelled illustration of the Earth globe which you could use toexplain the international system of time keeping to a primary orsecondary class.

Research: Keeping Time

What methods were used to keep time before the invention of modern clocksand watches?Describe one of these in detail. If possible you may be able to make a model.How did Melanesians and Polynesians keep track of time and seasons?

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EclipsesThe occurrence of lunar and solar eclipses are generally well publicised in advance.To understand how these events occur, and especially why they do not occur asfrequently as the normal textbook diagrams suggest they should, construction ofscale models is useful.

Activity 6.4 Modelling eclipses

1. Commence with any convenient world globe. As the moons diameteris approximately one quarter (1/4) that of Earth you need to select asphere of appropriate size. If necessary, a white balloon inflatedappropriately will serve well.

2. It is essential that the Earth-Moon distance in your model is also toscale. This distance is approximately 9-5 times the Earths circumfer-ence. Take a length of cotton, and wrap it nine and one half timesaround the world globe used in your model. This length of cottonrepresents the scale distance between Earth and Moon in your model

3. Find a large enough space, and set up your Earth-Moon system modelwith moon in the same plane as Earths equator. A slide projectionplaced as far as possible off to the side and in the same plane as Earthand Moon will serve well as a model sun.

Solar EclipseWith the Moon between Sun and Earth, observe how the moonsshadow falls on the Earth.

Questions1 Does the moons shadow cover all of the Earths hemisphere facing

towards the sun? Explain.2 Spin the model Earth, and estimate how long a solar eclipse might last at

any point on Earths surface. Research this topic and explain anydifference between your estimate and recorded values. Remember theangular size of the sun and moon and that the Earth rotates at 15 perhour.

3 Move the moon slightly, about 5) above or below the equatorial plane ofEarth. Does your model suggest that a solar eclipse would still occurunder these circumstances?

4 Remember that Earths axis is inclined at 23.5 to the orbital plane ofEarth. Move the projector slightly above or below (say up to20) tosimulate the orientation of Sun, Moon and Earth at various seasons. Doesyour model suggest that a solar eclipse will always occur when the moon isnew? Explain.

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Lunar EclipsesWith the Earth between the Sun and the moon, the Earths shadow may fall on themoon. Use models to explore how the Earths shadow might eclipse the moon.The photographs shown below will assist with your thinking.Questions1 Does Earths shadow cover all of the moon hemisphere directed towards

the Sun? Explain.2 Move the moon slightly above or below the equatorial plane of Earth

(say 50) Does your model suggest that a lunar eclipse would still occurunder these circumstances?

3 Research the occurrence of partial lunar eclipses. Arrange your modelto show how such an event occurs.

4 The Moons orbit is tilted approximately 5 to the plane of Earths orbitaround the Sun. Explain why lunar eclipses do not occur every time themoon is full, but do occur sometimes when the moon is full.

Figure 5.4. A series of photographs showing alunar eclipse from partial to total. The red colouris due to refraction of light around the edge ofthe earths atmosphere. (Photographs: JohnBroadfoot).

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7. Our planets

Discoveries by famous astronomersAncients have long realised that some stars appear to move relative to other stars.We now know these are actually planets. Johannes Kepler was the first astronomerto fully explain the orbits of the planets in detail. Keplers famous laws were basedon 20 years of rigorous observations by Tycho Brahe, a Danish nobleman. Keplerwas a mathematician and a critical thinker beyond his time. In fact we can alsoattribute modern calculus to Kepler. You should read you text or other astronomybooks for more information on the significance of planets to the ancients and thediscoveries in modern times.

Revisiting Brahe and Kepler

1. Read suitable astronomy books and prepare a summary of the importantdiscoveries of these two famous astronomers.

2. Compare the differences between the way these two persons madecontributions to our knowledge of planets.

Finding planets in the night skyBecause the planets revolve about the Sun, we are able to make periodicobservations of them. The movement of our own planet enables us to see each ofthe planets at some time throughout the year. This apparent motion is through theecliptic or zodiacal constellations. The centre line represents the Suns positionrelative to the Earth. When planets are viewed in the evening sky we describe theirposition as so many degrees east of the Sun (Elongation East) whereas, when theplanet appears in the morning sky we describe its position as degrees west of thesun (Elongation West). If a planet is on the opposite side of the Earth as is theSun then it is in opposition to the Sun. A conjunction occurs when planets appearto join together. Positions of Greatest Elongation occur for the planets inside ofthe Earths orbit. These are Mercury and Venus. These planets reach a maximumaltitude above the horizon at regular predictable times.The inferior planets, Mercury and Venus, are best seen at elongation positionsgreater than 20 from the Sun due to the effect of twilight before sunrise and aftersunset. The bright star-like object frequently seen above the eastern horizon beforesunrise or above the western horizon after sunset is Venus. Mercury is bestobserved at Greatest Elongation during the shorter daylight months when there isalso less twilight, that is, winter.The Inferior planets, because of the position of their orbits inside that of the Earth,also exhibit phases like the Moon. At Greatest Elongation positions, Mercury andVenus appear as quarter phases, and at closer positions to the Earth, as crescents.

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They appear as gibbous phases when further from us than the Greatest Elongationpositions. Venus and Mars both show marked apparent size changes due to thelarge changes in distances separating them from Earth. The superior planets arealways outside of Earths orbit therefore phases are not seen. These planets are themost readily seen at higher altitudes in the night sky.

Activity 7.1 Observing the planets

1 Observe the position of the visible planet(s) at sunset or sunrise forone week.

2 Use your hand span to estimate the position, azimuth and altitude, ofthe planet(s) from the horizon.

3 Mark the positions on a sheet of white paper on which the horizonhas been drawn. (You have previously established the cardinal pointsat your home and the magnitude of your hand span.)

4 Record your observations in an appropriate manner to clearly showyour data and observations.

5 For each observation include a sketch showing clearly the relativeposition of the planets to your horizon and the cardinal points.

6 Try to estimate the time each planet sets each day and record thisdata. Confirm your estimations using a suitable software program.

Questions1 How do planet positions change during one week?2 Identify the planets by referring to an ephemeris, star charts or a

suitable software package..

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SUN

Figure 5.5. Elongation and appearance of inferior planets

Venus in opposition

Mercury

Venus appears as acrescent

Venus at greatestelongation west of thesun

Earth

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3 Which planet has moved the fastest relative to the others? Why?4 Why do the planets appear to be in a straight line?5 What time did each planet rise and set each day?

A famous conjunctionOn June 17, 2 BC one of the most spectacular and closeconjunctions of planets ever witnessed by mankind occurred.to observers on earth it would have appeared as a singlemagnificent star in the western sky over Bethlehem. It wouldhave easily been seen from Babylon and signalled, to the Magi,an important event in history.

(Jerusalem Christian Review, Vol. 7, Issue 7)

There has been much debate about when the birth of Jesus actually occurred.Astronomical evidence, calendar adjustments and the scriptures suggest that aconjunction of planets as being the most probable major celestial event at that time.In fact other significant events occurred about the same time. The Magi of Babylonwere preoccupied with the movements of the sun, earth and planets and placedgreat significance on alignments or conjunctions of the planets. In the same periodas the Venus-Jupiter conjunction, the planet Jupiter rose to meet Regulus (King star)on three occasions making a halo loop over the star. This convinced the Magi that agreat event had occurred. In fact, astronomers, using the scriptures and veryaccurate ephemeral software, have been able to date the actual birth as earlyevening, 11 September, 3 BC.

7.2 Planetary conjunctions

To further investigate the motions of planets through the constellations the accuratepositions of the planets over a series of dates may be provided by an Ephemeris ormay be calculated using a suitable computer program. These positions expressedas celestial coordinates may then be plotted on a celestial map using the rightascension and declination positions for each position. You will be repeating some ofthe work done by Brahe and Kepler.Sets of data have been provided. These data are the positions of the planets Venusand Jupiter between 1 April and 31 May 1998.

1. Plot the data on a suitable star chart labelling each data point with theappropriate date.

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2. Join the points to indicate the movement of these two planets with respectto the background of stars.

Jupiter VenusDate Right Ascension Right Ascension

hr:min:sec Declination hr:min:sec Declination

3 April 23:01:40 -704 21:53:07 -1146

7 April 23:04:33 -658 22:09:27 -1042

11 April 23:07:50 -638 22:25:56 -933

15 April 23:11:03 -618 22:42:29 -817

19 April 23:14:13 -559 22:59:06 -656

23 April 23:17:18 -540 23:15:47 -530

27 April 23:20:18 -522 23:32:29 -401

1 May 23:23:14 -504 23:49:15 -228

5 May 23:26:04 -446 00:06:03 -052

1. Describe the apparent motion of each planet with respect to the backgroundstars.

2. At what date do the planets appear to be very close to each other?3. Explain the apparent motion of these planets in terms of the heliocentric model

of the solar system. You should draw a sketch to show the relative positionsof the earth, sun and the two planets.

4. At what position (label on the diagram) would Venus appear as a crescent ifviewed through a telescope.

5. When photographing Venus with a telescope astronomers need to use veryfast shutter times such as 1/2000 second. How can this be when Venusappears to be very small and so far away?

There are also many computer programs that can be used to accurately predict therising and setting times of planets. There is also of course the daily newspaper!

7.3 Another conjunction

1. Prepare a star chart showing the best times to view Saturn and Venus on 29May 1998.

2. Calculate the approximate rise and/or set times for these two planets.

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3. Prepare for school students the best viewing times, instructions to enable themto find the planets and a list of interesting points about these planets.

4. Describe using a sketch how Venus and Saturn will appear in a telescope.5. Draw and label a heliocentric diagram to show the paths and positions of

Saturn and Venus.

7.4 The scale of things!

In this activity you will construct a scale model of the planets for display. You willneed pieces of different coloured card to represent the planets, compass, pencil,scissors and glue or tape. You will work in pairs and each pair will be assigned aplanet for this activity.(a) Complete the table below by referring to an astronomy reference. Calculate

the scales sizes for your model.For distances from the sun: 1 cm = 1 million kilometresFor diameters of sun and planets: 1 mm = 500 kilometres

Object Distance from sun Scale distance Diameter Scale diameterSun not applicableMercuryVenusEarthMarsJupiterSaturnUranusNeptunePluto

(b) Using suitable colours of cardboard construct each planet to scale.(c) Prepare and fasten a label to each planet summarises the main features. (You

may need to hang the features on a separate card as a mobile for the smallplanets).

(d) Along a suitable hallway or verandah measure and mark the distances fromthe sun for each planet. Hang each of your models at the scale distance.

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7.5 The Terrestrials

The terrestrial planets are also known as the inner planets which are mercury tomars. Read the accounts of these planets in the relevant chapters of your text andanswer the following discussion questions.Discussion questions

1. Why does the solar nebula theory predict that planetary systems arecommon?

2. Why dont terrestrial planets have rings and large satellite systems like theJovian (outer) planets?

3. How does the solar nebula theory explain the dramatic density differencebetween the terrestrial and Jovian planets?

4. If planets formed with one of the first stars to form in our galaxy, how wouldthese planets be different from the planets of our solar system?

5. How does plate tectonics create and destroy the Earths crust?6. What evidence do we have that plate tectonics does not occur on Venus or

Mars?7. If we visited a planet in another solar system and discovered oxygen in its

atmosphere, what might we predict about that planets surface?8. What does density tell us about the planets internal structure?9. Compare the densities of the outer planets to the inner planets. Why is there

such a difference?10. Some planets have a strong magnetic field and some are only weak. What

does this indicate about the structure and/or composition of these planets?11. Draw a diagram to explain why Mercury and Venus show phases similar to

the Moon.12. Planets like Mercury and Venus show evidence of lava flows. What does

this suggest about there history?13. Compare and contrast the atmospheres of the terrestrial planets. Suggest

possible factors which may have contributed to changes in the atmospheresof these planets since their formation.

14. It has been stated in some sources that Venus atmosphere could once havesupported life. What evidence is there to suggest this?

7.6 The Jovians

The Jovian planets are also known as the outer planets which are Jupiter to Pluto.Read the accounts of these planets in the relevant chapters of your text and answerthe following discussion questions.Discussion questions

1. Why are the belts and zones on Saturn less distinctive than those on Jupiter?2. How can a satellite (moon) produce a gap in the rings of Jupiter or Saturn?

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The Changing Sky

3. What evidence do we have that catastrophic impacts have been common inour solar systems history?

CometsThe sudden and unheralded appearances in our sky, the abnormal paths they takeacross the celestial sphere, and the extraordinary spectacle that a large comet canproduce, make comets the most remarkable of heavenly bodies visible to theunaided eye.Comets are nebulous bodies that revolve around the Sun in elongated ellipses ofteninclined at a considerable angle to the orbits of the planets. A comet may appearsuddenly in any direction from the depths of space, rush past the Earth and roundthe Sun, and disappear in possibly quite another part of the sky. Because of thegreat distance between the Earth and a comet it moves slowly among thebackground stars.A typical comet consists of a bright nucleus, surrounded by a luminous cloud, thecoma. The coma and nucleus together make up the head. The tail, if present, isusually a fainter streak of cloudy material joined to the head. The tail always pointsaway from the Sun. Comets are always brightest when near the Sun, and are thenseen in the western sky at sunset, or in the east at sunrise, their tails pointing upwardfrom the horizon. The luminosity of a comet is due to solar radiation - gas moleculesare ionised by the Suns ultraviolet radiation and the nucleus thus emits light. Thesolar wind forces gas and dust away from the comet and these shine by reflectedlight forming the coma and tail. As a comet approaches the Sun, its tail growslonger and larger, and the whole object brightens. As it swings around the Sun, thetail, still streaming away from the Sun, swings round also, so that it precedes thecomet in its outward journey. Most comets are not seen like this. Most are smallnebulous objects, vague in form, and without any kind of central condensation.Size. Even small comets have a head diameter of at least 15,000 km, the averagesize being from 50,000 to 250,000 km in diameter. The biggest ever observed wasthe great comet of 1811, whose enormous diameter of almost 2,000,000 km wasgreater than the diameter of the Sun itself. The tails of great comets are even moretremendous; the great comet of 1843 had a tail 320 million km in length, over twicethe Earth-Sun distance. The apparent size of a comet depends on both its actualsize and its distance from the Earth and Sun; thats why the great comet of 1861had a tail no less than 118 in length, although it was by no means the largest ofcomets.Mass. Although comets may be enormous in size, their masses are always small.This may be estimated by the absence of perturbative effects, e.g. Comet Lexellcrossed the orbits of the inner satellites of Jupiter in 1779, yet although the orbits ofthe satellites were in no way affected, the orbit of the comet was completely alteredand it has never been seen since. It is concluded that the mass of the comet musthave been less than one-millionth the mass of the Earth. Because of their smallmasses and large size, the mean density of comets must be extremely low - abouthalf an ounce per cubic mile.

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EARTH AND SPACE

Composition and Structure. There are several theories as to the physicalstructure of comets. Here we will mention only the two most acceptable models. Inthe first model, the nucleus is a mixture of ice-conglomerate consisting of a highlyporous mass of solidified gases or ices of water, ammonia, methane, carbon dioxideand dicyanogen. The mass also includes some solidified particles. The secondmodel sees the comet nucleus and coma as a gigantic particle cloud of gas and dustparticles whose mean distance of separation is large but concentrated towards thecentre, giving rise to the appearance of a nucleus. The fact that most comets havelittle or no central solid mass is shown by the comet of 1862 and Halleys Comet of1910 which both passed between the Earth and Sun, but nothing was seen of themas they passed across the face of the Sun. By planetary standards, the mass ofcomets is very small but they are by no means negligible. The collision of the Earthwith a comet moving at several km per second would be catastrophic. The greatexplosion at Tungus, Siberia, in 1908 which was equal to a multi-megaton atomicexplosion, is consistent with the theory that it was due to collision with a smallcomet.The spectra of comet nuclei show prominent lines of sodium also neutral iron, nickel,chromium, silicon, manganese and neutral and ionized calcium. The coma and tailshow C2, CH, CN, OH, NH, NH2, CH2 and the ions N2+, CO+, CH+ and OH+, allof which are unstable and owe their existence to the extremely low density andfreedom from collisions.Origins of the Comets. The precise origin of comets is not known. They maycome from interstellar space, perhaps the residue left over from ancient starformation or perhaps they are created by shock waves as the Sun and other starscollide with dense interstellar clouds of gas and dust. On the other hand, they maybe the rubble left over from the formation of the Solar System; perhaps greatnumbers of them orbit at a distance well beyond the orbit of Pluto. In either case,perturbations due to the motion of stars, can throw a comet on a path towards thesun. If the path of the comet takes it too close to a planet its orbit will be altered,and the comet captured, as is the case for Comet Halley and other periodic comets.Subsequent encounters with the planets can further alter a comets path. In this waysome periodic comets are lost back into interstellar space.

7.7 The comets

Read the accounts of comets in the relevant chapters of your text and answer thefollowing discussion questions.Discussion questions

1. How do observations of meteor showers reveal one of the sources ofmeteoroids?

2. What evidence do we have that asteroids are possibly fragments ofplanetoids?

3. How does the composition of meteorites give us an insight into planetarystructures?

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The Changing Sky

4. What evidence is there to support the dirty snowball model of the nuclei ofcomets?

5. Why do short period comets tend to have orbits near the plane of the solarsystem?

6. Describe the differences between impact craters of comets and meteorites onthe earths surface. Name some examples of craters in Australia.