Beginners Guide to the

Astronomy A Beginner's Guide to the Universe, 8e Eric Chaisson, Steve McMillan

(Solutions Manual All Chapter)

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Copyright © 2017, 2013, 2010, 2007 Pearson Education, Inc.

Chapter 0: Charting the Heavens

The Foundations of Astronomy

Outline

0.1 The “Obvious” View 0.2 Earth’s Orbital Motion 0.3 The Motion of the Moon 0.4 The Measurement of Distance 0.5 Science and the Scientific Method

Summary

This chapter covers the view from Earth, including constellations, the celestial sphere, and the apparent motions of the Sun and stars. The actual motions of Earth that give rise to those apparent motions are then discussed. The motion and appearance of the Moon are addressed in the third section. This chapter concludes with distance determinations and a discussion of the scientific method.

Major Concepts

The view from Earth  Constellations  The celestial sphere Earth’s orbital motion  Rotation  Revolution  Angular measurement  Precession Motion of the Moon  Lunar phases  Eclipses Measuring distance  Triangulation  Parallax Scientific theory and the scientific method  Observation  Theory  Prediction

Teaching Suggestions and Demonstrations

One of the challenges in studying astronomy is developing the ability to view the universe from different perspectives, primarily the perspective we have from Earth, where we see the Sun and stars rise in the east and set in the west, and the perspective from outside, where we see Earth spinning on its axis and orbiting the Sun. Use plenty of models and diagrams in teaching this introductory material in order to help your students practice shifting viewpoints. Lots of new vocabulary is introduced in this chapter; take the time to define new terms. 2 / 4

Chapter 0: Charting the Heavens 9

Copyright © 2017, 2013, 2010, 2007 Pearson Education, Inc.There has been an emphasis among the astronomy educational research community that teaching approaches in college astronomy classes should be more learner-centered. An easy way to start to incorporate this approach is the book Lecture-Tutorials for Introductory Astronomy 3/E by Prather, Slater, Adams, and Brissenden. This book contains many in-class exercises that students may work on in small groups. There are exercises on positional astronomy, solar vs. sidereal day, seasonal stars, the ecliptic, and phases of the Moon as well as additional topics that will be mentioned throughout this book. It takes a lot of consideration to decide how to use such materials, but research shows that it will benefit most students for the classroom to be more learner-centered.

Section 0.1

Your students will all have heard of constellations and will probably be able to name at least a few.Emphasize that the stars in a given constellation are probably not physically close to each other in space; they just appear close to each other as seen from Earth. The stars in each constellation were grouped together by observers in ancient times, and we continue to use nearly the same groupings today. You can pass out or project a sky chart without constellations drawn in and challenge students to make up their own.

Asking students what their zodiacal sign is can be a good way for the students to feel connected to the sky, even though very few might actually follow astrology. Consider using Starry Night College to demonstrate how the zodiacal constellations lie across or near the ecliptic line. Show how the sky view will change during the year. Be sure to let students know that their zodiacal constellation is associated with where the Sun was located when they were born, but it is about a month off due to precession of the equinoxes. This is illustrated in Figure 0.8.

It is also interesting to compare names of northern and southern constellations. The northern constellations are typically named for animals and mythological characters. The Southern Hemisphere sky includes constellations such as the telescope, the microscope, and the octant. Ask your students if they can explain the difference. The constellation names we have inherited today derive from northern observers. The northern constellation names, therefore, date from ancient times, but the southern ones date from the early travels made by northern explorers to the Southern Hemisphere.

If you have time, explain a few of the myths that involve whole families of constellations. The story of Orion, Taurus, and the Pleiades is a good one, as is the story of Cassiopeia, Cepheus, Andromeda, Cetus, and Perseus. These are all constellations that students can find in the night sky, depending on the time of year you are teaching the course. Provide star charts and encourage your students to find major constellations in the night sky throughout the course.

The concept of the celestial sphere is an important one. We are missing depth perception when we look out at the night sky. If you have one, bring in a transparent model of the celestial sphere with Earth inside and point out the north and south celestial poles and the celestial equator. This is a good time to discuss Polaris and clear up any misconceptions; often, introductory astronomy students believe the North Star must be the brightest star in the sky.

Introduce students to right ascension and declination by comparing these to latitude and longitude.Emphasize that the celestial coordinates are attached to the sky. Over the course of a night, stars move from east to west and the coordinate system moves with them. Look up the coordinates of a few well- known stars (including Polaris) and help students determine their positions. Ask students to compare the two different methods of describing star locations, by coordinates and by constellation, and discuss the advantages of each.

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10 Instructor Guide for Chaisson/McMillan, Astronomy, Eighth Edition Copyright © 2017, 2013, 2010, 2007 Pearson Education, Inc.Section 0.2

Students usually know the terms rotation and revolution but often confuse them, so take a few moments to define these terms. Consider using the word “orbit” instead of “revolution” to help avoid confusion.Students will also probably know that Earth takes a day to turn on its axis and a year to orbit the Sun, but will not know the difference between a solar day and a sidereal day, or a tropical year and a sidereal year. Use lots of diagrams, such as Figure 0.7, to help explain. Models also help. Demonstrate rotation and revolution with globes, or bring students to the front of the class to model Earth’s motions. For instance, one student can spin around (slowly) while also orbiting another. Ask the class to concentrate on one point on the Earth, say, the spinning student’s nose, and imagine when it is lit and when it is dark.Use this model to explain day and night, sidereal vs. solar days, and why different constellations are visible in the night sky during different months.

Figure 0.9 is also an important one. Make sure students understand that it shows the apparent path of the Sun on the celestial sphere. Use models of Earth and the Sun (or just two spheres) to help explain how Earth’s tilt changes the position of the Sun in the sky as Earth orbits the Sun. Emphasize that the terms solstice and equinox can each refer to both a point in time and a point in space. The summer solstice, for instance, is the point on the ecliptic where the Sun is at its northernmost position, but we also use the term to refer to the time and day when the Sun is at that point. Students will be most familiar with the latter meaning, and know that the summer solstice occurs around June 21.

Begin your discussion of seasons with an informal, multiple-choice pre-quiz. If you’d like to make this pre-assessment a bit more formal, author Paul Green discusses more ideas in his book Peer Instruction for Astronomy starting on page 11. He also includes “concept tests” for the seasons as well as the celestial sphere and time conventions used in astronomy that can be used throughout the lecture. These can be used in conjunction with additional “clicker questions” that are provided with the instructor materials. During your lecture, ask students what causes the seasons, and include in the answer choices both the correct response, namely, Earth’s tilt, and a common misconception, the distance from Earth to the Sun. If significant numbers of students choose the distance answer, make sure you address this misconception and explain why the different distances from Earth to the Sun do not affect the seasons.Many students are surprised to find that, in fact, the Earth is farthest from the Sun during the Northern Hemisphere summer. Bring in a flashlight and shine it directly down on a tabletop or on the floor, and then shine it at an angle to show how the angle of the Sun’s rays affects solar heating. Go back to your model of Earth orbiting the Sun to show how the length of time the Sun is up in the sky also changes as the seasons change.

A gyroscope or top makes a good demonstration of precession. Find Vega on a star chart and point it out to students to help them get a sense of the scale of the change. Precession is also responsible for the fact that the zodiac constellations no longer correspond to their astrological dates. The heliacal rising of Sirius, in the constellation Canis Major, was an important date in the ancient agricultural calendar, but this no longer occurs on the same date today.

Angular measure is very important to astronomy. Discuss More Precisely 0–1 carefully. Demonstrate angular measure by holding up a penny. At a distance of about 1 meter, a penny subtends an angle of about 1 degree. Students can hold up a penny and see what objects at different distances in the classroom have an angular size of about 1 degree. Also have students try this at night and estimate the angular size of the Moon, half a degree. Go over angular measurements and then try several examples. Many problems throughout the text use the equations in this section, so it is worth spending some time with them to ensure student understanding.

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