Although the Jewish philosopher Moses ben Maimon (Maimonides) does not offer an alternative model, in his Guide to the Perplexed written in 1190 (4951 on the Hebrew calendar), he argues that neither Aristotle's or Ptolemy's of how the planets move provide a good model (see Figure 2.1):

If what Aristotle has stated . . . is true, there is no epicycles or eccentric circles and everything revolves around the center of the earth. But in that case how can the various motions of the planets come about? . . . How can one conceive the retrogration of a planet, together with its other motions, without assuming the existence of an epicycle? On the other hand [Ptolemy's hand], how can one imagine a rolling motion of the heavens or a motion around a center that is not immobile? This is the true perplexity!

- Moses ben Maimon, Guide to the Perplexed 2:24

We take part the Earth-Moon-Sun system. The relationship between their positions at various times determines some common phenomena such as seasons, moon phases, and day length. You will use physical models to explore these relationships.

You may be familiar with the solar system model in which the Earth is located at the center. Below are two other versions of how the planets (P) go around the Earth (E). These models were based on ideals rather than careful observation. Egotistic as we humans are, we had a need to place ourselves at the center of the universe. In the Eccentric model, the Earth is not at the center of the solar system, but was stationary and all the planets and the sun as well orbit around the sun. In an attempt to explain why Mars exhibits a retrograde motion, the Deferent Model has the planets looping around an orbit about the Earth. None of these explained why Mercury and Venus have phases like the moon. Only the heliocentric (sun-centered) solar system can explain these phases.

1. Figure 2.1: Two earth-centered models of the solar system. On the left is Aristotle's eccentric model, on the right is Ptolemy's epicycle model. Neither provide a good model of how the planets move based on centuries of observation.

1. A Model of the Sun-Earth-Moon System -- Phases of the Moon

You will construct a physical model of the Sun-Earth-Moon system. Materials for your model will be at the appropriate activity station. The purpose of this model is to investigate the phases of the moon.

There are four phases of the moon: full, new, first-quarter, and third-quarter. Look at your textbook to see how they appear in the sky.

Activity:

Use a small sphere affixed to a stick to model the moon. Locate the 'observer' cut out at the end of this week's activity and cut it out. Affix the observer on a stick. Use the 'observer on a stick' to represent you standing on the earth's surface. A lamp acts as the sun.

Hold the observer about half a meter from the 'sun'.

Suppose the Figure 2.2 represents a top view of the model. This is what you would see if you were far from the earth, but above the North Pole. Hold the moon at the location indicated below.

In the Figure 2.2, blacken in the shadowed part of the moon.

1. Figure 2.2: A top view of the Sun-Earth-Moon model.

Your job is to deduce what the 'observer on a stick' located on the Earth will see. Blacken in the shadow of the moon's face (in Figure 2.3) that the 'observer' sees when looking into the sky.

Figure 2.3: The moon as person on the Earth sees.

Question: Compared to the Textbook, the phase of the moon is _________________.

Figure 2.4 represents another top view of the model. Holding the moon at the new location indicated below, blacken in the shadowed part of the moon.

Figure 2.4: A top view of the Sun-Earth-Moon model.

What the 'observer on a stick' see now? To indicate this, blacken in the shadow of the moon's face in Figure 2.5.

Figure 2.5: The moon as person on the Earth sees.

Question: Compared to the Textbook, the phase of the moon is _________________.

You know what to do in Figure 2.6.

1. Figure 2.6: A top view of the Sun-Earth-Moon model.

Again, blacken in the shadow of the moon's face (in Figure 2.7) when the moon is located as it is above.

Figure 2.7: The moon as a person on the Earth sees.

Question: Compared to the Textbook, the phase of the moon is _________________.

Once more blacken in the shadowed part of the moon when it is located as shown in Figure 2.8.

1. Figure 2.8: A top view of the Sun-Earth-Moon model.

When observers looks into the sky, what will they see when the moon is located as it is in Figure 2.8? Indicate what they see in Figure 2.9, below.

Figure 2.9: The way a person on the Earth sees the moon.

Question: Compared to the Textbook, the phase of the moon is _________________.

Questions:

What is the time between two successive full moons (in days)?

What is the orbital period of the moon around the earth (in days)?

What is the time between a full and a new moon?

Draw in the locations of the full moon and the new moon in Figure 2.10. Label them. Fill in the shadowed part of the moon in each case. Indicate which locations (beside one curved arrow) the moon is waning -- where it is getting closer to a new moon. Indicate which locations (beside the other curved arrow) the moon is waxing -- where it is building up to a full moon.

1. Figure 2.10

If the full moon is in the west. what time of day must it be? It must be in the ____________________ .

Write a brief explanation as to why we see the phases of the moon.

1. The Seasons

The Baroque composer Antonio Vivaldi wrote a pervasively familiar set of concertos called "The Seasons". Each of the set of four is devoted to one of the four seasons -- spring, summer, autumn, winter. In Concerto No. 1, mimics songs of birds, spring thunderstorms, and a spring zephyr. In the summer concerto, Vivaldi uses changes of meter (first 3/8 and later 4/4 time) to describe the exhaustion caused by the summer heat. Autumn, the season of harvest, Vivaldi uses the motifs of a tribute to Bachus -- God of Wine -- via a feverish dance and The Hunt using the horns to herald the event. In Concerto No. 4, the frigid winds blow in an almost melody-less illustration.

The Venetians of Vivaldi's time all understood the effects and moods of the seasons, but how did they come about? In this activity, we look closely at an explanation.

First, we must dispel an old misconception. Figure 2.11 shows a sketch of the earth's orbit from a top view far above the sun. The orbit of the earth is slightly elliptical as shown below -- it is not a perfect circle, its a 'squashed circle'. However, the 'squashed-ness' of the orbit -- its eccentricity -- is greatly exaggerated in Figure 2.11. The common misconception is that when the earth is at point A, it is closer to the sun, and therefore it is summer on earth. If you have ever went in the wintertime to South America or Austrailia, you would discover it is summer there! The misconception would have it summer in both the northern and southern hemispheres.

1. Figure 2.11

The common misconception fails on another point. The eccentricity of perfectly circular orbit is zero, whereas a 'flat circle' has an eccentricity of one. The eccentricity of the earth's orbit is 0.0167, which as much closer to zero than to one. In conclusion, the orbit of our planet is so close to a perfect circle, that you probably cannot draw a circle on paper more circular than the earth's orbit -- not even with a compass!

You will construct a physical model of the Sun-Earth system. This model will not be to scale. Materials for your model will be at the appropriate activity station. The purpose of this model is different than the purpose of making a scale model of the solar system. The purpose of this model is to investigate the correct reasons for earth's daily and seasonal cycles.

Activity:

Locate the photometer (a light brightness meter) about one meter from the lamp. Suppose the lamp represents the sun and suppose the light-sensitive surface of the photometer represents the surface of the earth. Position the photometer as indicated in Figure 2.12a.

When light hits the surface of the earth (more or less) perpendicularly, we call this direct sunlight. The term direct is rather misleading, but it is commonly used in textbooks.

For direct 'sunlight', the photometer reads: _____________________.

Now orient the photometer as indicated in Figure 2.12b.

When light hits the surface of the earth at an angle, we call this indirect sunlight. The term indirect is also misleading. What is actually happening is that the energy per unit area remains the same (nothing with the lamp changes), but when the surface is at an angle so the effective area is smaller. (To test this, look at a note card or sheet of paper end-on, then tilt it and you see less of the note card and it appears to have a smaller area).

For indirect 'sunlight', the photometer reads: _____________________.

Use a 'sphere on a stick' as the earth and the lamp as the sun to 'build' a sun-earth system model. It should look something like Figure 2.13.

Successively place the 'earth' at locations A, B, C, and D. Deduce what season it must be in the northern hemisphere. Note that the tilt of the axis of the earth should not change. The axis will always lie along the same line as indicated. (This is a result of conservation of angular momentum -- it is the same reason why the axis of a gyroscope will always tend to point along the same line.)

1. Figure 2.13: A perspective view of the sun-earth system. Sol is the official name of our star according to the ASA.

Questions:

Does more sunlight (and therefore more infrared radiation) hit the surface of the earth when the light is direct or indirect?

Why do the northern and southern hemispheres have opposite seasons?

Fill in the table using your observations:

Location of Earth in Figure 2.13	Season in the Southern Hemisphere	Season in the Northern Hemisphere
A
B
C
D

Use your model to explain what a complete earth day is. Describe what you did and how you did it.

Use your models explain the seasons on earth. Use diagrams in your explanation.

GOALS

This set of activities focuses on measurement and careful observation in science and applies it to astronomy and stargazing.

After completing today's activities you should appreciate the celestial coordinates of right ascension and declination, be able to identify common stars and constellations you can view from our latitude, learn how to use star maps to determine what stars and constellations are visible, and learn how to observe and sketch celestial objects in the night sky.

INTRODUCTION

Ancient cultures observed stars and other celestial objects. They had different methods and objectives for studying the stars than we do. Our motivation is, however, essentially the same: to learn about the world around us and to apply that knowledge to our everyday lives. Today we have modern technological instruments to help us with our observations and data collection. There are many observations we can make of celestial objects that do not require any sophisticated instruments. Careful observations with the unaided eye can allow us to determine our location and movement in our local corner of the universe. Simple instruments like binoculars can help provide more information than you can obtain by just using your sight alone.

The sun is the closest star to us. It is so bright during our daytime that we cannot see other stars. Daytime astronomy allows us to focus on observations of the sun, such as, its change in position and movement through the day and throughout the seasons.

The night sky provides us with the opportunity to make observations of other stars, our planets, and other celestial objects (such as star clusters, nebulae, and other galaxies). We can categorize the structures of the universe into ever-larger systems, each containing the previous system. The Earth-Moon system, the solar system, the galactic arms of our galaxy, the Milky Way Galaxy, the local group (of galaxies), the Andromedia Group (of local groups), clusters (of groups), superclusters (of clusters), and strings (of superclusters). Using only crude instruments, we can observe celestial objects in our solar system -- the sun, planets, and moons. We can also observe, under good conditions, objects in the Orion galactic arm -- other stars and nebulae (gaseous clouds which are remnants of exploded stars or matter gathered up by the rotation of the galactic arms). There are several star clusters we can observe that are not in the arms of the Milky Way, but orbit the center of our galaxy. Finally, with the unaided eye you can see one galaxy in the Northern Hemisphere if you are far from the glare of city lights.

Our galaxy is disc shaped; it is about 80,000 light-years in diameter and 5,000 light-years thick. We are located about half way from the center of the disc. All the individual stars we see in our night sky are in the Milky Way galaxy and most of them are in Orion arm. The next nearest star is nearly 4.3 light-years away from us. The study of stars helps us to understand our own star and how our planets formed.

There are other celestial objects or phenomena in the daytime and the night sky that are visible to us from earth. You may have noticed the moon, planets, meteors, comets or eclipses during your observations of the day and night sky. If you have been at different latitudes you may have noticed that the stars visible in the Southern Hemisphere are not the same as those in the Northern Hemisphere.

1. Celestial Coordinates

Initial Questions

What is the significance of the number 23.5 degrees when we speak of the earth's rotation?

Explain these:

North Pole -

South Pole -

Tropics of Cancer and Capricorn -

Prime Meridian -

Equator -

How do we identify arbitrary locations on a map?

We were hoping you would answer latitude and longitude. Come to a group consensus as to the meaning of latitude and longitude are. Explain these terms. How (and from what location) are they measured?

latitude -

longitude -

Among your group, deduce what the latitude and longitude of Monmouth.

To locate stars in the sky, we use a similar system of coordinates. (See Figure 1.1.) We imagine a line painted across the sky directly above the equator called the celestial equator. We pretend there are marks directly above the north pole and south poles called the celestial north pole or celestial south pole. Angle in degrees from the celestial equator towards the celestial north pole (or celestial south pole) and measure the declination as "+" for north ( or "-" for south). The declination is analogous to the latitude. Analogous to the longitude, we measure the hours and minutes of right ascension from the international date line counterclockwise.

Questions

What is the declination of the North Star (also called Polaris) so named as it sits almost directly on the celestial north pole?

Why is the right ascension measured in hours and minutes (from 00:00 hours to 24:00 hours)?

To tell your neighbour where a particular star is located, you might say its elevation is 20 degrees up from the horizon and, from north along the compass directions, 135 degrees azimuth. Why can you not expect a person living in Mexico or Alaska to be able to locate this star using these instructions? What about someone living in Europe? How should you describe the location

of the star to these folks?

This summer, near the longest day of the year, I was gazing at the constellation Hercules. It was directly overhead at mid-night. What was its elevation? Based on the information given, deduce what its declination and right ascension are. (Hint: We are nearly at latitude 45 degrees and are 18 hours from the international date line.)

Elevation -

Declination -

Right Ascension -

1. Classifications of Stars

Initial Questions:

Are the stars in a given constellation close to each other, or do they appear that way from our location?

In your group, list all the ways you can think of to classify stars.

Astronomers often categorize stars in terms of their age. Embryonic stars, found nebulae, are called proto-stars. These are only detectable with special interments. A star will spend most of its lifetime in the main sequence stage. Our sun is a main sequence star. These stars are typified by their moderate size, brightness, and yellow colour (as seen by our eyes). As a star approaches middle-age, its expands and cools becoming a red giant star. As we will see later in this course, cooler corresponds to redder, hence the name red giant. The last stages of a star's life depends on its mass. For small mass stars, the final fate may be a brown dwarf, a small dead and dark core. Moderate mass stars, such as the sun, will explode in a nova explosion and result in a white dwarf. A white dwarf has a low light output since it is rather small, but it is very hot and appears bluish-white. Larger mass stars may supernova in a brilliant release of matter and energy and eventually form a neutron star or even a black hole. It should be noted that only main sequence, red giant, and white dwarf stars are detectable with the unaided eye.

From the above discussion, you see that the colour (or temperature) of a star may be a useful categorization. Astronomers have quantified the colour into spectral types. Spectral type G stars are 70% to 120% of the mass of the sun (a main sequence star). Red giants are fall into spectral classes K and M, and white dwarfs fall into spectral classes B and A. Since size (volume) of a star is correlated with its colour (and therefore temperature), there's not much use in categorizing the volumes of stars. The "brightness" of a star, however, directly relates to is mass (the amount of matter it contains) and its total energy output.

When we look up at the stars and judge a star's "brightness" we are actually measuring its apparent magnitude. Since the light from a star radiates in all directions, we see only a portion of its light. The further away a star is, the dimmer it appears. Since the mass of a star is related to its total energy output, perhaps it would be more useful to remove the distance factor from the apparent brightness. The absolute magnitude corrects for the distance, so that a star 5 light-years away having the same mass (and energy output) as the sun has the same absolute magnitude as the sun (which is less than 10 light-minutes away). Oh, drat. Our eyes see on a logarithmic scale so that we can detect a very large range of lightnesses. For instance, to double the absolute magnitude of a 10 Watt light bulb, you would need a 100 Watt light bulb (not a 20 Watt bulb)! Try it sometime! (Why in dining room lamps do we use many more than two bulbs?) If we really want to compare the masses of different stars, we need to remove our perception of 'brightness' and use the luminosity to directly measure the total energy output of stars. Thus, a star with twice as much mass has twice the luminosity.

Activity:

First, note the Wattage (brightness) of the light bulb. The bulb is a _________ Watt bulb.

Stand next to the lamp and note its "brightness".

Move to the opposite side of the room and now note the "brightness of the bulb.

Questions:

Is the Wattage listed on the light bulb more closely a measure of the apparent magnitude, the absolute magnitude, or the luminosity? Defend your answer.

When you looked at the bulb's "brightness", did you measure the apparent magnitude, the absolute magnitude, or the luminosity? Defend your answer.

Looking up at the sky, what colour would a red giant be? A white dwarf? A main sequence star? (Hint: You may answer in terms of bluish-white, reddish-white, or yellow)

1. Star Maps and Locating Celestial Objects

You should be armed with two laminated star maps. The circular star map is a view of the sky as if you were sitting at the north pole looking up. We call this a polar map. It shows from 90 degrees declination (overhead - the center of the map) down to 30 degrees declination (going radially away from the center in concentric circles). The long map is a view as seen from the equator -- an equatorial map. The thick line running down the center represents the celestial equator. Above this line are stars to the north of the celestial equator, that is those with positive declinations. You should notice the numbers of right ascension from 0 hours 00 minutes to 23 hours 59 minutes (on some maps from 24:00 to 23:59) running from right to left.

To make our lives easy, we notate the location of a star first by is right ascension then its declination. For instance, a star with a declination of 22 degrees south of the celestial equator and right ascension of 18 hours, 42 minutes would be written: 18h42m - 22°.

Verify that:

Aldebaren, in the constellation Taurus, is at 4h35m +17°.

Fomalhaut in Pisces Austrinus is at 22h54m -30°.

Activity: Find the following stars and galaxies on the star chart and note their locations.

Alpha Centauri, a triple star system and the nearest star to the Sun. All three are main sequence stars. Alpha Centauri A closely resembles the Sun in spectral type (G), size and absolute magnitude. Alpha Centauri B is similar to the Sun but somewhat cooler and dimmer. Proxima Centauri, the closest to us, is a red dwarf. Alpha Centauri is in the constellation Centaurus and can be seen from the tropics and Southern Hemisphere.

Location ______________________

Sirius, a binary star and brightest star in the sky. Sirius A is a main sequence star hotter and brighter than the Sun. Sirius B is a white dwarf. Sirius is in the constellation Canis Major in the Southern Celestial Hemisphere, but can be seen from Oregon.

Location ______________________

Betelaeuse, a red supergiant in the constellation Orion. It is about one-half as hot as the Sun but 460 times larger.

Location ______________________

Andromeda (M31), a spiral galaxy and nearest large galaxy to our Milky Way galaxy. It is dimly visible in the constellation Andromeda in the Northern Celestial Hemisphere.

Location ______________________

Large Megallanic Cloud, the nearest galaxy to the Milky Way galaxy. It is visible in the Southern Hemisphere as a small, hazy patch of light.

Location ______________________

Regulus, the brightest star in the constellation Leo. Regulus is seen around sunrise in early October.

Location ______________________

Antares, a red giant and brightest star in the constellation Scorpius. Antares sets in the early evening in October. Will you be able to see the red coloration of Antares?

Location ______________________

1. DO AT A COMPUTER Constellations During the Seasons

A CD-ROM came with your textbook. Install Starry Night on a computer near you. You are welcome and encouraged to use NS 216 computers. Run Starry Night.

On the main tool is the 'location' button. Click on this button. You are able to set the latitude and longitude for your desired location. Monmouth is located at latitude 44.54^o N and longitude 123.90^o W. Set the coordinates to these values.

Locate the display window. If you aren't sure where it is, click on the 'display floater' button from the main toolbar. The display window will either disappear or appear. Click the 'display floater' button until you can find and see the time window. Click on the "constellations button" a couple of times. When the "constellations button" is 'on' you see them in the sky. Play around with the rest of the buttons and see what they do. When you are done experimenting, be sure the everything in the display window is turned on including the "constellations button", except the "Equator button" is best turned off.

Locate the "N" (N is for North) button at the upper part of your screen. This will move your view so that you are looking East. Play around with the W,E,S,Z buttons and see how they work. Return to the N view.

Locate the time window. If you aren't sure where it is, click on the 'time floater' button from the main toolbar. The time window will either disappear or appear. Click the 'time floater' button until you can find and see the time window.

Move the mouse around the time window, until you see the pop up saying "time step unit" (its probably under the word 'mins' or 'hours'). With "time step unit" showing, click the mouse. Use the up & down arrows that appear to change the units to "days". Move the mouse over the number to the left under the number. Click on this number and change it to 30.

Press the NOW button from the time window. Note that the time window shows the current time.

Quickly sketch the 'sky' including the constellations you can see from this S view. Note the date and time of this picture.

From the time window, figure out with is the single step button. (A pop up message appears when the mouse is held over it for a moment). Click on the single step button and the time advances one month!

Every 2 months from your first sketch, sketch a new version of the sky. Label each sketch with the time and date.

------

You should be armed with only a star booklet. The star chart booklet shows which constellations are visible at a specific time for each month of the year. Each page represents a different time of the year for 45 degrees latitude (roughly Monmouth).

In the center of each map is the overhead point -- 90 degrees elevation. That is what you would see directly over your head when you stargaze at the time indicated on the chart. Around the circumference of the star map you will find little buildings and trees. These represent the horizon. The horizon is also marked with compass directions of north, south, east, and west. These directions are actually azimuth angles (0 degrees for north, 90 degrees for east, etc.). Assume that 0 degrees elevation is at the horizon and 90 degrees elevation is at the overhead point. Constellations that are approximately halfway between the overhead and horizon points could be estimated to be at an elevation angle of 45 degrees. If you know which compass direction they are at you will be able to predict the approximate location in the night sky you could find a particular constellation.

The constellations in your star charts show those that are visible from 40 degrees N latitude. Western Oregon University is very near 45 degrees N. That means the constellations in the north will be a little higher in the sky and those in the south will be a little lower than what the maps show.

A circumpolar constellation is one that is visible year round from a specific latitude.

Activity

Use your star maps from January through December to find four circumpolar constellations as seen from Monmouth, OR. We suggest you first choose one (randomly?) and then check to see if it appears on all the maps.

Fill in Table 1.1 by indicating approximately where in the night sky you would locate them.

Give the approximate number of degrees elevation (zero at the horizon and 90 degrees at overhead) or use the words high (near the overhead point), middle, or low.

Also provide their compass direction. For compass directions try to use more than just N. S, E, and W. For example, SW may provide a more accurate location than just S or W.

*Some of the constellations that you locate on the star map may be the same one's you will be locating in your lecture activity "Observing The Night Sky". Writing compass directions that are more accurate now will help you find them at night!

1. Table 1.1

Questions

Based on the data in Table 1.1, describe how the constellations appear to move through the night sky during the year.

Note the position of Polaris, the North Star. Describe its position throughout the year. Why do you think it does this?

Tear out this page. Then, cut out the observer and affix him to a stick.

GOALS

Once completing this week's activities you should be able to describe similarities and differences among planets of our solar system. You should be able to create scale models, and make sketches that reasonably portray observations of components of the solar system. You will be able to create graphs to communicate and interpret data from a variety of sources. Finally, you will be able to use physical models to determine the reasons for the phases of the moon, the seasons, and the length of the day.

INTRODUCTION

We have sent unmanned spacecraft through the solar system, landed robot space probes on Mars, Venus, and the moon, landed people on the moon, and have sophisticated telescopes to obtain data. We know that each planet and satellite (moon) has unique physical characteristics that set them apart from one another. We also know our solar system exhibits some regular patterns. During this laboratory you will try to discover some of these patterns. Much of the numerical data about our solar system, such as planetary size or distance from the sun, is so large that you will need to work with scale models. By studying planetary data we can compare and contrast conditions on other planets and their satellites (moons) to those of earth.

PRE-LAB ASSESSMENTS

INDIVIDUALLY

What do you already know about the Earth's place in the solar system?

List the planets in order of increasing distance away from the sun. Circle the planet that is smallest. Underline the largest planet.

SUN,

Which planets can you see without the aid of instruments like telescopes/binoculars?

Least as many physical characteristics (such as mass) that you think planets have.

Think of at least two ways to group or classify the planets according to physical characteristics. Try it.

What are the two main properties of planets that you would want to know about?

Why do we have seasons on Earth?

What causes the phases of the moon?

IN YOUR GROUP

Compare your lists of planets made in order of increasing distance away from the sun. Make a list that your group agrees with

SUN,

Which planets have the members of your group seen without the help of instruments?

Which planet does your group think is smallest? ___________ Biggest? ______________

Compare the different ways you were able to classify planets.

Which properties of planets you wanted to find out about did your group members have in common? Which were different?

What reasons did your group give for the reason for seasons?

What reasons did your group give for why the moon has phases?

Planets are a bit different than stars. Many decades before we visited our planets with spacecraft, we knew their basic terrain, chemical composition, and atmosphere. Conjecture as to how we deduced these things and what information was available to do it.

1. Scale Model of The Solar System

An astronomical unit, AU, is the average distance the Earth is from the Sun. That distance is 93,000,000 miles, 8.3 light-minutes, or 150,000,000 kilometers. It is convenient to work with AUs because the real distances are in numbers that can be cumbersome to deal with. Table 2.1, below, shows the AUs for planets in our solar system, using the Earth's average distance as the basic unit of 1 AU. You might find the orbital distances in terms of light-minutes more illuminating (pun intended). Choose which system of units (the column) you feel more comfortable with. The size of a planet is also an appropriate addition to a scale model of the solar system. The table lists the radius (double it to get diameter) of each planet in kilometers and in millionths of AU. Your group will construct a scale model of the solar system based on average distance to the sun and diameters of the planets. Your model must fit in the hallway (54 meters long), the classroom, or outside (weather permitting). You must decide the scales you will use for your model.

1. Table 2.1: Solar System Data

* Note: In 1998, the Astronomical Society of America removed Pluto from the list of planets.

Questions

What scale did you use for your distance?

What scale did you use for your planet size? (Hint: Consider the diameter of the sun and the model sun.)

What pattern did you notice about the spacing of the planets from the Sun?

What general pattern did you notice about the relative sizes of the planets?

1. Table 2.2: The Planet Parameters Table

1. Table 2.3: Table of Other Useful Parameters**

1. Classifying the Planets

Study the solar system parameters information in Table 2.2. The table provides information scientists believe to be true about the planets in the solar system based all the latest technology to help them. By looking carefully at the data in this table you should be able to find some patterns, similarities, and differences among the planets in our solar system. Some questions will assist you in thinking about what is considered a pattern, similarity, and difference. You will need to find more than just those. You should also look over Table 2.3 which contains other useful parameters. Also, you should investigate the samples of air, water or ice, typical rock, and lead (which approximates metal at high pressure). Since all these samples have the same volume, you can investigate the effect of density directly. Please pick each one up and compare their masses (and therefore, their densities).

Questions

Use four physical properties of the planets in the solar system to group them into general categories or in general ways. (For example, try the atmospheric composition as one of the four physical properties.)

Make a general statement from the properties that could be cited as a pattern in the solar system.

Which planet would float in water? _____________________________

(Hint: Less dense object float in more dense fluids.)

How long is a day on Jupiter? _____________________ on Venus? _____________________

How many Earth years go by before one Jupiter year has passed? ________________________

Which 2 planets account for 90% of the total mass of the planets? ________________________

Which planet seems unusually hot considering its distance from the sun? ___________________

By looking at the data, suggest a reason for this extreme hot temperature.

Estimate the density (from the mass) of the four samples by picking them up. How many times larger or smaller do you think the densities are compared to water? How do your guesses compare to Table 2.2?

Air seems to be ____________________ times less dense than water.

Rock seems to be ____________________ times more dense than water.

Metal at high pressure seems to be ____________________ times more dense than water.

How do your guesses above compare to Table 2.2?

Table 2.2 provides information about the density of common materials found on Earth. Compare the densities of metal, rock, ice, and gas to the average planetary densities. What can you guess about the composition of each of the planets? Answer this by filling out Table 2.4. (Hint: You can answer in terms of mostly metal, rock, ice, or gas; or combinations of these.)

1. Table 2.4

1. The Ecliptic And The March Of The Planets

This was unfinished at press. There may be additional handouts given in class.

1. The Satellite Matching Game

This was unfinished at press. There may be additional handouts or instructions given in class.

Matching moons, classify planets by colour (pictures) and, therefor, by atmosphere.

Use the laminated/place in plastic folders in the 3 ring binders planet pictures.

INTRODUCTION

We are here, but the sun and other stars are way out there. How do we learn about them? The only way is through 'remote sensing'. There are two categories of remote sensing. One is 'active' -- we can go to the sun and planets with probes such as Cassini or the Mars Lander which is very expensive. Or we can look 'passively' at the information sent here from the objects in the distance. When you see a star or planet in the sky you might say 'what a beautiful light in the heavens...'. But what sorts of information can you uncover about that beautiful light?

This week we explore the major aspects of how astronomers use light to explore strange new worlds.

A DESCRIPTION OF HOW A WAVE TRAVELS

To describe a wave, let us first consider the 'life' of a wave. It usually starts with an object oscillating. The wave forms when the object's oscillations are coupled via coupled vibrations. Once formed, the wave travels from its origin to its destination. Of course, the wave must be detected by some sort of detector in order for it to reveal its past history. How can you detect the simple harmonic motion of a wave using a detector? To help you understand this, consider the following rather lengthy example:

A stone is thrown into a quiet pond. Near the edge of the pond a small duckling is floating serenely. A water wave is produced where the stone was cast, it travels away from that point, eventually to reach our duckling. As the wave passes our friendly waterfowl, it bobs up and down, oscillating with simple harmonic motion. Our fine feathered friend knows by experience that there was a disturbance in its quiet little world.

To investigate if our duckling is indeed oscillating with simple harmonic motion, let us consider placing a harness about the quacking bird, tying a string to the harness, running the string over a pulley, and measuring the motion of the pulley over time. Refer to Figure 3.1.

The (vertical) position of the infant waterfowl can be deduced from the number of degrees the pulley has turned over time from its initial position. A graph of its position over time should reveal a graph similar to what you will plot in one of the our other exercises!

1. Figure 3.1

GOALS

After completing the activities this week, you will have an understanding of what sorts of information astronomers have available to them from the stars. Most fundamentally, you should become familiar with the role and importance of making astronomical observations and how they are made. After this week you should know some basic wave properties with regards to light and various telescope designs.

PRE-LAB ASSESSMENTS

Pre-Lab Assessment 1: Astronomers know a good deal about the star Rigel: its distance to us, the details of its motion, its mass, its density, its temperature, its energy output, and its elemental composition. Clearly, we have not visited this star (or any other star besides our own). Certainly there are no Rigelians sending us updates about their star to us via messages in bottles. Conjecture about what form the information is in that allows us to deduce these things. Exactly what clues from this information do we have in order to deduce these parameters: a star's motions, mass, density, temperature, energy output, and composition.

Pre-Lab Assessment 1: Planets are a bit different than stars. Many decades before we visited our planets with spacecraft, we knew their basic terrain, chemical composition, and atmosphere. Again, conjecture as to how we deduced these things and what information was available to do it.

1. Waves Transfer Energy

This exercise should convince you that waves transfer energy and illustrate the concept of coupled vibrations. The apparatus consists of two demonstrations. The first one is a heat lamp, the second is a set of tuning forks.

WARNING: PLEASE DO NOT STRIKE THE FORKS AGAINST A HARD OBJECT. SET THEM DOWN ONLY ON THE FOAM PROVIDED! Only use the rubber hammer provided to strike them!

As you know (or will learn) light can have many different wavelengths, some invisible to the eye. Heat is one of these invisible light waves. "Heat waves" are referred to as infrared waves.

The heat lamp works this way: Electricity from the wall outlet heats up the lamp's filament, which causes the electrons in all the atoms of the filament to oscillate at many different frequencies. Each oscillating electron couples its vibrations to its surroundings in the form of oscillating electric and magnetic fields. These fields are self-creating, and leap-frog their way out into the room. This is, of course, the electromagnetic-magnetic wave we call light. Some of the frequencies of the waves emitted by the lamp are visible, but many more are infrared waves.

Activity

Place your hand in front of the lamp. What do you feel?

Working with light waves isn't always easy, so sometimes we use other types of waves.

Find the tuning forks. Pick up both forks holding them by the handle only. If you hold one of the fork tangs, it will not vibrate correctly. Listen to one fork and verify that it is quiet.

Now strike the other fork with the rubber hammer. Place the two forks close together, but not touching. Hold them with their tangs parallel about one fork's width away. After a few seconds, place the fork you listened to earlier to your ear and listen again.

Questions

What does infra mean? Check your local (Latin) dictionary. Knowing the meaning of 'infra', is the frequency of infrared higher or lower than visible light, and in particular red light? What about the wavelength of infrared light in relation to visible light wavelengths? (Isn't the word infrared odd -- a mixture of Latin and English.)

What did you feel when placing your hand in front of the heat lamp? Why are you now convinced that waves, infrared waves in particular, transfer energy from one place to another?

Questions, Continued

In detail, how were the infrared waves detected by your hand? Hint: If you try to make electrons in your hand oscillate, they will strongly resist. This resistance manifests itself, ultimately, to exciting your nerves.

Describe your observations in a short paragraph and describe how the vibrations from one fork are 'moved' to the other fork. What happens to the mechanical energy of vibration of each of the two forks initially and after the few seconds you held them close to one another? Conjecture on how you are able to detect the waves.

A so called 'black light' is actually an ultraviolet light source. By ultraviolet we mean light invisible to humans. Conjecture on how those 'black light' posters work. How is it we see green light from the poster when it is illuminated with invisible light? If you are not familiar with a 'black light' poster, hopefully we will have an example around.

UV (ultraviolet) light sunburns your skin by damaging your skin cells. The sun is very far away, how is this possible? Conjecture using the effects and terminology you have learned today.

1. Speed Of A Wave

We have devised a way to measure the speed of light the same way you might measure the speed of your car on those 'odometer test areas'. You 'measure the distance and the time it takes to go that distance. To get the speed you divide the distance by the time. Unfortunately, this experiment is too challenging for this laboratory. Our Modern Physics students do this experiment. Here is what they did last year:

In the speed of light experiment, we place a modulated laser (one that pulses on an off rapidly) at one end of the hall. At the other end, we place a mirror where the light reflects back down the hall. Near the laser, we place a detector which measures the difference in time between when the laser sends a pulse and when it arrives from down the hall and back. The length of the hall is 51.4 meters, so the light travels a total distance of 102.824 meters. The time recorded is 3.45 x 10^-7 seconds. Thus, the speed of light is 2.98 x 10⁸ meters/second. Note that the accepted value is 2.99897 x 10⁸ meters/second.

So, measuring the speed of light this way is too difficult. Hence, we will do this same experiment using sound waves instead.

You will use a computer-controlled black box containing a speaker and a microphones. A wave (actually a series of pulses) will be generated by the computer and speaker. Each pulse will travel a known distance, reflect off a wall, and return to the black box. The microphone contained in the black box will be register each pulse. The time difference between when each pulse leaves the box and when it is registered by the microphone is measured by the computer.

Activity:

Using the computer, measure the time between when each pulse leaves the box and the microphone 'hears' the pulse. Please refer to the instructions on the computer screen in order to operate this computer-controlled experiment. Your instructor will brief you on how to do this.

Measure the distance (in meters) between the microphones. Do this to within the nearest millimeter (0.001 meter).

The distance (in meters) between the box and the wall: _______________ meters.

The 'round-trip distance' (in meters) that each pulse travels: _______________ meters.

The average time (in seconds) for pulses to travel the round trip distance: ____________ seconds.

From the definition of velocity (speed), compute the speed of the sound wave in air.

Your measured velocity (speed) of the sound wave in air: ______________ meters/second

Questions

Mathematically show that my Modern Physics students computed the right number for the speed of light using their experimental values for the distance down the hall and time it took to travel that distance.

Measure the temperature of the air with a thermometer. Look up from a table (or calculate) the speed of sound in air for the temperature you measured. How does it compare with your measured speed of sound? Please write this value in the blank at the bottom of page 10.146 for future reference.

What are the implications of observation that light doesn't travel instantaneously from the distant stars to our telescopes?

1. White Light And The Visible Light Spectrum

Light from the stars and planets can contain a wealth of information about the object it came from. Its not so easy to look at star light, so we will have to be creative.

This station consists of several light sources and a set of spectroscopes. A spectroscope measures the wavelength of a light wave. If there are many light waves of differing wavelengths, the spectroscope will register all the (visible) wavelengths. Your job is to measure the wavelengths present in each source.

The first source is an incandescent tungsten filament lamp. It should be noted that a hot tungsten filament acts as a black body light source. With your instructors help, set up the spectroscope with this source. You should see a full spectrum or range of visible wavelengths. We apologize for the difference scales on the spectroscopes. The ranges below should cover 750 to 450 nanometers. You will have to add (or remove) zeros to the scales to come up with numbers in this range.

Activity I:

Make observations of the incandescent filament lamp. Measure the range of wavelengths that comprise 'red light' in nanometers. Repeat this for orange, yellow, green, blue, and violet.

red light __750__ to _______ nanometers,

orange light _______ to _______ nanometers,

yellow light _______ to _______ nanometers,

green light _______ to _______ nanometers,

blue light _______ to _______ nanometers, and

violet light _______ to ___450_ nanometers.

A hydrogen discharge lamp is provided as your second source. With your instructors help, set up the spectroscope with this source.

WARNING: THE HYDROGEN AND OTHER DISCHARGE LAMPS HAVE A LIMITED LIFE. TURN THESE LAMPS OFF UNLESS YOU ARE ACTUALLY USING THEM.

WARNING: KEEP CLEAR OF THE LAMP WHEN IT IS OPERATING. THE HIGH VOLTAGE IS DANGEROUS.

LEAVING DISCHARGE LAMPS ON LONGER THAN 60 SECONDS AT A TIME MAY RESULT IN DEDUCTION OF POINTS ON YOUR LAB!

Activity II:

First make a note to include in your report as to the apparent colour of the source you see with your eyes.

Does what you see looking through the spectroscope surprise you? Why?

Measure all the wavelengths the hydrogen lamp, again in nanometers.

Activity II, Continued:

Observe the fluorescent lamp through the spectroscope. Make careful observations so that you might compare the lamps in detail. Record your observations below.

Finally, you can view a neon (or other ) discharge lamp. Make a note to include in your report as to the apparent colour of the source you see with your eyes. With the hydrogen lamp in mind, how does the neon (or other) lamp differ? If time and equipment allow, study some of the other discharge tubes. They contain other gaseous elements. Record your observations below.

Questions

Refer to the ranges of wavelengths you measured for red through blue wavelengths. Compare this with your textbook or the spectrum poster. How close are you? Why might your answers differ from these references?

List the colours of the visible light spectrum from longest to smallest wavelength.

Compare the incandescent and fluorescent light sources. Note the wattage of each lamp and visually compare their brightness. Explain why their brightness and wattages don't jive. (The one with the lower wattage appears brighter!) (Hint: Hold your hand next to each lamp.)

A continuous spectrum is one in which all wavelengths (colours) are represented. A discrete spectrum is one that does not have all wavelengths represented, rather it has only a discrete number of wavelengths. Which source(s) has a continuous and which a discrete spectrum? Which source(s), if any, has partly a continuous and partly discrete spectrum? Explain your answer.

Recall the activity where we studied the black body spectrum and also ask yourself if the different gasses in the discharge tubes produced the same spectrum or a 'signature' spectrum different for every element. Now answer this: How can light be used to determine what is inside a star? (Your answer should be long enough that it might not fit in this space!)

Look up the spectrum of the sun. (You might have to ask me for it.) Is the spectrum discrete or a black body spectrum?

1. Lens & Image Characteristics

WARNING: HANDLE LENSES ONLY BY THEIR EDGES. PLACE LENSES ONLY ON A SHEET OF PAPER TO PREVENT SCRATCHING.

IMPROPER HANDLING OF THE LENSES MAY RESULT IN DEDUCTION OF POINTS ON YOUR LAB!

In this activity you are provided with two different lenses and you supply your powers of observation.

The curvature of the lens greatly affects the magnifying ability. Investigate the large curvature (the thin one) and small curvature lens (the thick one). Focus a scene through the windows on the opposite wall. To do this hold a lens against the far wall facing the windows, then move the lens slowly away from the wall until you see an image form on the wall. This is illustrated in Figure 3.2. Note the distance from the image to the lens and the image's magnification in particular.

1. Figure 3.2

Questions:

Describe the image that you see. In your description use terms like somewhat magnified or greatly magnified, upright or upside-down.

The field of view is how much of a scene that can be imaged. If you can see more of a scene, the field of view is larger. Look at a piece of graph paper on the table through the small and large lens. Hold both lenses the same distance away; maybe 4 cm? Compare the field of views of the two lenses in your report.

Questions:

Compare the field of views of the two lenses.

Measure the focal length of the provided lenses. When an object is placed sufficiently far enough away to call it 'infinitely far away', the image will form at the location of the focal length of the lens. Choose an object very far away (>10 meters) such as objects outside the windows or a light bulb on the other side of the room. Hold the lens flat against the wall opposite your object (the wall needs to be light in colour). Move the lens slowly away from the wall until an image of the object forms on the wall. Carefully measure the distance (in meters) from the lens to the wall. This is the focal length. Report the focal length in your report. Don't forget to measure both lenses.

The focal length of the large curvature (the thick one) is _______________ meters.

The focal length of the small curvature (the thin one) is _______________ meters.

The f-number of a lens is (focal length in meters)/(clear diameter of lens in meters). A lens with an f-number of seven is written: f/7. Determine the f-number for the long and short curvature lenses. Please don't confuse f-number with the focal length, f.

The f-number of the large curvature (the thick one) is _______________ (no units).

The f-number of the small curvature (the thin one) is _______________ (no units).

Questions

Deduce and relate the relationship between the curvature of a lens, the magnification of the image it creates, and its focal length.

Which has the better field of view a large curvature or a small curvature lens?

What effects the field of view?

What is the relationship between the f-number and the field of view?

Why do National Geographic photographers use those really wide lenses?

Suppose we have a lens that is 0.02 meters in diameter. We then, using black tape, cover up the edges of the lens so that light can pass through only the inner 0.01 meters (in diameter). What happens to the f-number? Does it increase or decrease?

1. Telescopes

WARNINGS: TELESCOPE ARE EXPENSIVE PRECISION INSTRUMENTS.

DON'T BUMP OR JAR THEM. DON'T TOUCH ANY GLASS OR REFLECTIVE METAL SURFACES! IMPROPER HANDLING OF TELESCOPES MAY RESULT IN DEDUCTION OF POINTS ON YOUR LAB!

Being the Earth-dwelling creatures that we are, we don't always have the luxury of popping up into orbit every time we want too look at the stars (see the 'Observing The Night Sky' lecture activity). Below are descriptions of smaller, Earth-based telescopes.

The refracting astronomical telescope is made of two converging lenses (see Figure 3.3). Incoming parallel rays from a distance star are focused to an intermediate image. The eyepiece lens is then used to prepare the light to be viewed by your eye. Your eye's lens focuses the light onto the retina forming an image that your brain can interpret. Notice that since the intermediate images is inverted, the 'sky' will appear 'backwards'. The magnification of a telescope is large if the intermediate image is large and if this image is viewed through an eyepiece (magnifying glass) of large magnification. The magnification of a refracting astronomical telescope is the ratio of the focal length of the objective to the focal length of the eyepiece.

Figure 3.3

For terrestrial purposes, such as looking for whales or spying on your neighbour, the inverted image of the refracting astronomical telescope is rather inconvenient. To produce an erect image is simply to insert, between the objective and the eyepiece, an erecting system, which inverts the intermediate image The erecting system can be a simple converging lens (Figure 3.4), however the telescope becomes rather long (of the type favored by pirates). An erecting system that allows a shorter telescope is the combination of prisms shown in Figure 3.5 Binoculars are specified by both their magnification and objective diameter. Thus, a 7 X 35 binocular has magnification 7 and objective diameter 35 mm.

Figure 3.4 Figure 3.5

An alternative approach avoids the erecting system by using a diverging eyepiece, as in the Galilean telescope (Figure 3.6). Its advantage is that the distance between the lenses is actually less than a terrestrial telescope. However, the field of view is limited, so this technique is used in small, inexpensive opera glasses (but it was good enough to enable Galileo to discover four of Jupiter's moons).

Figure 3.6

The preceding telescopes all use objective lenses (so-called refracting telescopes). Large diameter lenses, however, create numerous problems. A technique that avoids all these difficulties is to use a concave, focusing mirror as the objective (the so called primary mirror). A smaller, secondary mirror is normally used to enable you to look through the telescope without getting your head in the way of the incoming beam. There are a variety of such reflecting telescopes, a few of which are pictured in Figure 3.7. In the very large reflecting telescopes, the astronomer (or a detector) can actually sit at the focal point of the primary mirror. Figure 3.7a shows a Newtonian telescope, Figure 3.7b shows a Cassigrain telescope, and Figure 3.7c shows the Gregorian telescope. Each have their advantages and disadvantages.

Figure 3.7

A technique to avoid the weight and cost of a single large mirror is to use a number of smaller mirrors in concert. The light collected by each of the separate mirrors is focused to a common image. The mirrors' sensitive alignment is accomplished by means of laser beams that accurately detect each mirror's position, computers that rapidly calculate any required position change, and motors that continually realign the mirrors. The Multiple Mirror Telescope on Mount Hopkins, Arizona, has six 1.8 meter mirrors that combined have the light gathering ability of about one 4.5 meter mirror.

PLEASE BE CAREFUL AROUND TELESCOPES! Don't bump them or pick them up. Don't touch any glass or reflective metal surfaces!

Activity:

Build your own telescope using the lenses and mounts. Choose only one. Here are some tips.

The Refracting Astronomical Telescope: Use one of the 5cm focal length lenses as the eyepiece, and the 20 cm focal length lens as the objective, separated by about 25 cm, with the eyepiece close to your eye. It may help to brace your hand against something, say the window frame. Notice the orientation and size of the image and the field of view and compare them to those obtained with the Galilean telescope. With a third hand you can try inserting the other 5 cm focal length lens about 5 cm in front of the eyepiece as a field lens.

The Galilean Telescope: Here use the -5 cm focal length (diverging) lens as the eyepiece, and the 20 cm focal length lens as the objective. The spacing between the lenses should be about 20 cm - 5 cm = 15 cm. It may help to brace your hand against something, say the window frame. Notice the orientation and size of the image and the field of view. Reverse the positions of the two lenses and look through them. Notice the large (wide) field of view, useful for a peephole in a door. (Of course, unless you live in a castle, you probably don't have doors 15 cm thick. Actual peepholes use shorter focal length lenses.)

Examine the telescopes and categorize them as to their type. For each, draw a sketch and identify the objective (mirror or lens), the eyepiece, and any other important internal mirrors or lenses. Use the space below or an additional page to record your work.

Your sketches of telescopes:

Questions

In a short paragraph, discuss this activity. Describe the telescopes you looked at and describe the one you built.

POST ASSESSMENT

Discuss in small groups the following questions. Formulate answers in your group, then each of you should write their own answers to the questions.

What sorts of information do astronomers have available to them from the stars? In what form does it come?

At the beginning of this week, we asked 'how do astronomers know so much about the star Rigel'? Based on what you have done today, what is your answer? How could we know its distance to us, the details of its motion, its mass, its density, its temperature, its energy output, and its elemental composition? (We don't expect a short answer!)