Astronomy by observation. An elementary text-book for high-schools and academies

Front matter

UC-NRLF

STFlOJfOMY OB SgRVATI ON

BY ELIZA A. BOWEN

Preface

Jtersu^y

THIS book has grown out of actual school-work, in which it was the teacher's object to make pupils studying elementary astronomy observe and think. The following are its chief peculiarities :

1. An efficient, easy, well-tried plan for teaching the constellations is described. Its use will obviate the necessity of a teacher doing work out of school-hours, by enabling students to become independent observers.

2. Careful directions are given when, how, and where to find the heavenly bodies. Their motions are described in the order in which they can be seen by an observer, and in familiar language. Thus, the text-book may be a guide to the observation of beginners.

3. The student is excited to thought. Facts are stated first ; theory afterward, as a deduction from the facts. The selection of subjects for the student's thinking is a little different from that of other school astronomies. The general principle governing this selection is to make the student understand what he can see. The author has also desired in some degree to separate the work of the elementary teacher from that of the college professor. To observe the facts from which Copernicus argued ; to discuss them ; to perceive how they prove his conclusions ; to use in this the simpler geometrical conceptions, seem to the author suitable elementary work. It would be excellent elementary work if it could be combined with some practical angular measurements of a simple kind on the heavens.

The author knows high-school work well. The thinking of this book is fairly within the comprehension of the students of our reasonably good schools. The professed study of the theory of astronomy, in which there is no thinking, is a counterfeit.

The book presumes in those who study it a little knowledge of elementary geometry, and of the refraction, reflection, and dispersion of light. As all high-schools teach as much of these subjects as is needed, it seemed better to take thus much knowledge for granted, than to make a digression for the purpose of presenting it.

The author has probably experimented as much as anybody in teaching elementary pupils by observation and by questions which drew them out to discuss theory. But much review is always required, and, in order to save time, a text-book is necessary for it. Also, we can not ring up the planets, like scenes in a theatre, to be studied during the school-session, and therefore the theory must sometimes be taught in advance of actual observation. The author hopes the book will be useful for these purposes to teachers who use'improved methods.

In writing it, another class of teachers has been much in view. In our high-schools and academies the teaching of astronomy is often in the hands of instructors who have little or no practical knowledge of the science. They are usually intelligent persons who would improve if the text-book were a guide to observation. %

Another class of persons has also been in view. Of late years a great spirit of study has arisen among young people out of school. Their situation is very favorable for the study of astronomy, since they are not bound by school hours and sessions, but can take the planets when they come. It is hoped that they will be encouraged to study the heavens if a sufficient guide to observation is furnished. No study lends itself better to teaching by correspondence than astronomy.

BEECHCROFT SCHOOL, TENN.,

Index

INTRODUCTION.

For Teachers and Private Learners.

HOW TO LEARN AND TEACH" THE CONSTELLATIONS.

WE can not help seeing the motions of the heavenly bodies, unless, like Bunyan's man with the muck-rake, we steadily look down. A professed study of astronomy which does not make us recognize these bodies and their motions, when we see them, may not be useless, but it bears some marks of counterfeit knowledge. A mere acquaintance with the constellations is a very subordinate part of the knowledge here recommended, but it has, besides its own value, a good deal of importance as a prerequisite to the rest.

There are two disadvantages in the way of a teacher who wishes to make his pupils in astronomy really study nature. He can not be with them at night without inconvenience, and work outside of school-hours. This is the first difficulty. Another is, the impossibility of having the planets brought out for inspection when he wants them, and also because, when they come, their motions are very slow.

After struggling a good deal with these disadvantages just mentioned, I found that by making young students learn the heavens as they do the maps of the United States or Europe, viz., by map-drawing, the whole of the first difficulty was obviated, and a large part of the second. They found the star-groups without trouble, for themselves. They were trained in observation, and they learned a great many of the motions incidentally. They became independent observers, and were so much interested in the practical study, that there was no doubt they would see and study for themselves whatever they could not see during the school-session.

No doubt a great many teachers can carry on this work quite as well as I can, or better ; but, for the benefit of those who can not, I will describe it somewhat in detail.

The brighter stars in each constellation, when joined by imaginary lines, form a figure which is easily recognized when once suggested. Such figures are drawn in dotted lines on the maps attached to this book. If the student takes one figure at a time, and draws it repeatedly, until he gains the power to reproduce it on paper from memory, rapidly, without erasures, and with a fair degree of rough correctness, he can easily find it for himself if it is a conspicuous constellation, and he has some general idea in what part of the sky to look for it. And even if it is not a conspicuous constellation, he can easily find it, if it is adjacent to a constellation already known, and in a known direction from it. Thus, beginning with conspicuous constellations, and proceeding to adjacent ones, and then to others adjacent to the last, they are all easily learned.

But this plan of teaching by map-drawing is not a mere substitute for what is called " pointing out the constellations," and is not adopted and recommended only because the other course is inconvenient or impossible when teacher and class lodge in different houses. It is so much the easiest way, that when instructor and pupils are already together in the evening, and the latter wish to learn the star-groups, the teacher will do well to sit in the house (as I have often done), draw the figures on paper or a blackboard, and send students out to locate the groups. At first the pupils feel helpless, and object ; but a little trial soon convinces them how easy it is. If any find a difficulty, the others help them ; and thus a teacher is spared additional work.

But mere drawing by the teacher is not sufficient, nor is that the plan recommended here. By the method described in the two preceding paragraphs, it is easy to have star-groups recognized at the time, but they will not be remembered, and must be taught again. Drawing by the pupil not only makes it easier to find them ; they can hardly be fixed permanently in knowledge during the school-study, except by repeated drawing from memory. Whenever students have a few leisure moments, they should be called upon to cover the blackboard with these figures, or to reproduce them rapidly upon paper.

In order to secure repeated observation, it is best to have the groups learned one at a time ; for, whenever the student goes out to find a new group, he is sure to look again at the old ones. The groups are fixed in memory, and also the habit of observation is strengthened. But the study of the motions gives far more interesting work than the mere identification of star-groups.

Any method of map-drawing already used in a school will answer for this purpose when carried out under the restrictions to be hereafter mentioned. The plan which I practice and recommend is called " drawing by dictation," now much practiced in the best schools. The teacher leads, standing at the blackboard, while pupils draw at desks in unruled exercise-books, which should not be used for any other purpose. When a teacher is wholly incapable of drawing even these simple figures, he can select some pupil to take the lead, who learns be-

ASTRONOMY BY OBSERVATION.

forehand how to draw this group. Command of a pencil sufficient for this purpose is very common in all schools. Of course, the teacher is present to direct. The leader at the blackboard draws one of the lines of the figure and pauses a moment, while pupils follow with pencil and paper. Then he draws another line, and they follow, and so on until all the lines are finished. These lines are dotted on the map, but, in the exercise described, they are drawn continuous but very lightly. As the leader draws, he calls attention to the dimensions and positions of lines. No erasure whatever should be allowed. This is an important dire'ction, for, unless it is observed, the teacher will be discouraged by the time consumed. It is not necessary to have more than a rough correctness, though, of course, pupils must not be encouraged to draw carelessly. After the lines are drawn, they must make the stars, the leader calling attention to the number and position. In the drawings made by leader and pupils, stars of the first magnitude are best represented by the symbol Q ; of the second, by * ; of the third, by X ; of the fourth, by •. In the " Description of Constellations," in the Appendix, there is given the number of first and second magnitude stars for each figure, and other information of value in studying them. After each constellation is drawn, the name should be written two or three times, and also the names of any first and second magnitude stars mentioned in the " Description." Then students should be called upon to repeat names aloud, separately and in unison. Without this exercise they struggle a good deal with the names.

The drawing of a constellation must be made two or three times rapidly, and then the students are directed to turn over a leaf and draw from memory. The whole exercise, properly managed, need not take more than ten minutes. It should take place on the morning of a day which looks as if it would be followed by a clear night. If rain and interruption occur, the exercise should be repeated when again there seems a chance for observation at night. Each repetition takes less time. After drawing a figure, the student is always told to turn it in every direction, and is warned that he can not be sure beforehand exactly how it will be turned.

The dictation exercise in drawing, which has been recommended and described, is a species of free-hand drawing, which affords valuable training to hand and eye. Students can certainly learn the figures by drawing directly from the maps, but they will make little cramped figures, and find it difficult to draw any others, even on the blackboard.

I hope I may be pardoned for telling of a test to which I put this method of teaching constellations. I took a class of fifteen children, whose average age was twelve years, but of whom three were only eleven years old, and I began to teach them the constellations at the beginning of the school year in September. Until a test was made at the beginning of November, I was never with them at night on a single occasion, nor had they any one at home who gave them help. They simply drew the figures and stars, and were drilled as here described. There was a good deal of bad weather, and another study took the place of star-learning, at least a third of the time. The lesson was half an hour long. At the first of November they knew perfectly every constellation which had been visible. They could tell where all the first and second magnitude stars were found. They knew nearly every third-magnitude star and a good many fourth. They could trace the ecliptic in the heavens, or draw it. They knew Algol, Mira, Epsilon Lyrae, the star in Draco which was the pole-star; Var in Aquila, midway between the poles ; and what made them all remarkable. They knew the points where the sun is found, December 22d and March zoth, and their names. They found no difficulty whatever in learning Pisces and Aquarius. Some had a little trouble with Hercules and Ophiuchus, but finally found them. They noticed the daily and annual motion of the stars, the revolution of the moon and her motion among the stars, and they watched with great interest the motion of Venus among the stars. They also noticed that the constellations of the zodiac seemed to approach the sun in succession, and other points not necessary to mention. Their enthusiasm was very great, and I am sure they are observers for life.

This book is, of course, not intended for children, and the subject is only mentioned to show what can be done by the method here recommended of promoting observation.*

For the benefit of inexperienced teachers, it is well to give some advice in regard to the constellations which it is best to begin with. Of course, the Great Dipper, the Little Dipper, and Cassiopeia should come first. Chapter II contains directions how to learn them. After these are learned, some conspicuous constellation must be selected and discovered. For the three autumn months, Pegasus is best ; for the winter months, Orion ; for spring, Leo Major ; for summer, Scorpio. By finding these in the " Description of Constellations, alphabetically arranged," Appendix A, the learner and inexperienced teacher will find hints how to proceed.

When the student has drawn and identified one of these four constellations, he can select from the map on which it is found some group adjacent to it. He next reads the account of the selected group in the " Description," page 80, and after drawing is prepared to find it ; when, by the help of maps and " Descriptions," he selects another group, draws and discovers it, and so on until all are learned.

Another plan, good for a learner without a teacher, or for a teacher to use with pupils, is to begin with the first-magnitude stars. Since these and the planets are the brightest stars visi-

* It is certainly desirable to have children of about twelve years old learn constellations, and to encourage them in that simple observation of motions which follows almost of itself. I have probably given as much time to this work for ten years, as any teacher in the United States ; and I at first thought of making a Primer of Astronomy for such children. I abandoned this idea because my experience showed that children could do nothing whatever with books or maps unless assisted by just as much oral teaching as would accomplish the result without the aid of such a book. To furnish such a book would, I think, merely encourage a particularly bad form of that prevalent book cram which pretends to be science teaching. I am quite certain that those teachers who make the use of this book that I design, will afterward begin the work orally with younger pupils.

HOW TO LEARN AND TEACH THE CONSTELLATIONS.

ble, any observer can find them at any time if he knows how many there are above the horizon. A private learner can use one of the maps at one of the definite dates and hours given on the maps. A teacher can tell his pupil how many ist m. stars can be seen at some early hour of the evening. They should know also how many are near enough to the horizon to be obscured by smoke or haze, if there is any. After students find them, a teacher can, from color, position, etc., name them intelligibly to students with the constellations to which they belong. Finally, the student draws the figure of each group, and identifies it. This plan interests students a good deal, because it begins with the most conspicuous stars.

In nearly every class studying astronomy at school there will be found a few brighter students who could use maps to identify constellations, without any help whatever from their teacher. But a majority of the students in such a class will not learn those groups unless their instructor makes them a subject of regular lessons and teaching. Also, in a large number of the schools for which this book is written, so limited a time is given to astronomy that the constellations must be learned as rapidly as is consistent with good work. In most such cases a teacher will do well to promote speed by going out with his pupils once or twice at night when they are learning the groups. But there is no economy of time in this unless these students have already made drawings of those groups which they are to identify. By no other method than that of repeated drawing can the constellations be so quickly, so perfectly, and permanently learned. Also, it will not do to rush too hastily over this part of the study. As soon as they know the constellations of the zodiac, they should practice drawing them on the ecliptic. For practice, it is best to draw, first, a straight line, and then draw the constellations on it in correct order and position. The ecliptic is the important circle, and the whole time in drawing circles should be given to it. For such knowledge of the other circles as is needed, they can use the maps.

No elementary science is so independent of expensive apparatus in schools as astronomy. The Copernican theory is the groundwork of all formal treatises on astronomy, and its author died before the invention of the telescope. No telescope used in ordinary schools could aid in its rational acceptance, except by showing the phases of Venus and the moons of Jupiter. The bearing of these on the theory could not be at all appreciated by a person who had not previously studied what can be seen with the naked eye. It is, of course, a pleasure and advantage, after learning what can be seen without a telescope, to see these objects, and also the rings of Saturn, the surface of the moon, and the resolution of some nebulae ; but I doubt whether it is any advantage at all until the student has used his unaided eyes. The most important need for high-schools seems to me to be some simple means of taking angular measurements on the heavens. This brings out a little the relation of the study to mathematics.

Of course, a large part of the information in an elementary astronomy comes from investigators equipped with the refined and complicated instruments of modern observation. In this case ordinary people can not see for themselves, but must take the facts on testimony. But here the phenomena seen can be so well represented by picture that ordinary people are under no great disadvantage in following with intelligence the conclusions of astronomers. Of course, we could neither intelligently accept the evidence nor appreciate the conclusions if we are entirely ignorant of the principles on which the instruments are constructed ; but these can be easily understood by the aid of a few inexpensive mirrors, lenses, and prisms.

It is my own experience that young persons have a sort of superstition about apparatus which looks complicated, and especially as if it cost a good deal of money. The feeling is diametrically opposed to the spirit of investigation, and therefore until they have become possessed of that spirit it is best to teach them with the simplest appliances.

Of illustrative apparatus, a globe, with the ecliptic traced on it in connection with the equinoctial system of circles, is important ; but there is a very small, cheap terrestrial globe now much used in primary schools which has the ecliptic traced on it for the purpose of using the globe to show the circles on the heavens. It can be made to answer the purpose, using an India-rubber band for the horizon when we wish to show the angles it makes with the ecliptic. The celestial horizon in nature is such a well-defined circle, and the sphere so plainly revolves through it, that there is not much lost by the globe not revolving.through the India-rubber band. Of course, a good celestial globe is a great advantage, provided it does not take the place of nature-study. Where we can see for ourselves, illustrative •apparatus is useful only to give definiteness to our ideas derived from observation ; but the study of nature should come first. I have many times seen expensive illustrative apparatus used so as to discourage observation. This was not intended, but practically this was the result.

SUPPLEMENT TO THE INTRODUCTION.

(NEW MATTER IN THE THIRD EDITION.)

NOTE BY THE AUTHOR. — Since the first edition of this book was publUhed, I have had much correspondence with teachers using it, in regard to certain practical problems which arise in the combination of observation with book-study. I think I shall add to the usefulness of the book by some discussion of these difficulties. I have given to their solution years of thought and experiment with classes, and I am quite sure that the plan I suggest is the best that the nature of the case allows.

When to learn Constellations. — In using this text-book, students should, of course, learn Chapter I before beginning observation. They should then suspend book-study to learn the star-groups, for it is impossible to study in nature the motions of the earth, the moon, and the planets, without knowing perfectly by sight the chief polar constellations and those

ASTRONOMY BY OBSERVATION.

belonging to the zodiac. In their study of the heavens, it is important to have students come as soon as possible to the zodiac, and in particular to those two zodiacal groups which at the time of that study may be found at dark just above the eastern and western sides of the horizon. On the apparent annual motion of these groups the reasoning of Chapter III is founded. This motion is very slow ; and, in order that students may perceive some degree of it when they reach Chapter III, they should learn the groups as soon as possible. To give time enough for the change produced by this motion to become perceptible, it is best for the student, before studying Chapter II, to learn thoroughly all the constellations visible between dark and bedtime.

What Period of Time devoted to Book-Study and Observation will give Satisfactory Results ?— I think that the mere text of this book could be learned in four months, or in less time. If more than six months were given to the mere text-book study, time would be wasted. But the observation contemplated in the book brings in some other considerations in planning the time and period of study.

In a year's time we can, with two exceptions, see nearly all of the phenomena described in Part I, pp. 10 to 52 of this book ; not so as to make subsequent observations unnecessary, but so that with some variations, easily comprehended, the continued observation will be largely a repetition of what has already been seen and understood. The exceptions are, that Venus and Mars can be seen as evening stars about every alternate year only. But the student can, without any serious disadvantage, be left to study Mars and Venus in nature after his school-work in astronomy has ceased. He is prepared to observe and understand the motions of Mars by the study of Jupiter and Saturn, which will always be visible during the school year. The motions of Venus are not complicated, and can be so visualized from description as to make the subsequent observation easy. Besides, Mercury can nearly always be seen as evening star in the spring, if the weather is good, and his motions help to make those of Venus understood. Under any circumstances it is desirable that students shall keep up observation of the heavens after leaving school ; and a sight of Mars and Venus is an incitement to do so, when they have been well instructed. Probably the best test of a teacher's work in astronomy (where he is free to do his best) is found in his success in creating a permanent habit of observation — not with a few brighter pupils only, but with students of average capacity. To create such a habit, a teacher must himself acquire it.

During five months, which is half the school year, and is the period allotted to the formal study of astronomy in a great many schools, the most important part of this observation can be made. But the observation of five months is not so complete as would be desirable.

To overcome the difficulty arising from these facts, I have tried two plans, either of which has some advantages. By one plan, the lessons in astronomy come on alternate days only, but last through the school year. But, in adopting this plan, it is important that students should be encouraged to give a few moments to observation on every clear evening at dark. By the other plan, the lessons in astronomy come every day for five months ; and afterward, at intervals, a few observation-lessons are secured.

How to make the Appropriate Observations precede or accompany their Related Portions of Theory Study. — Success in making astronomy a genuine study of nature depends on this, and my advice has been much asked about it. The plan which I recommend is the result of many years of thought, experience, and work.

It is impossible perfectly to accomplish the object, but with good management much more is possible than would at first be supposed. In the first place, part of the time of each lesson or " recitation " — ten minutes or more — must be given to the consideration of all such phenomena as Nature offers to us on that evening. Nature will not wait for us, and we must see phenomena when she presents them to us. In the time given, as described above, to the observation-study, the teacher should tell the student what to see and how to see it, and make sure that he has seen what in previous lessons he was advised to see. The teacher is not, in this branch of the lesson, to explain the causes of phenomena or to discuss the connection of these facts with theory. On almost any night we can see presented together facts which are discussed in every chapter of Part I of this book. The confusion would be inextricable if we undertook to explain these facts in the indiscriminate succession in which they come. But the mere seeing of the phenomena is so simple and vivid that there is no confusion whatever in observing with attention all that can be seen.

At the end of the ten or more minutes which are devoted to the direction of this observation-study, the book-lessons come, taking up phenomena in the more systematic order of the book. But this whole matter will be better understood, and the great simplicity and easiness of the work appreciated, by considering in detail the facts which a teacher is to make his students see. These facts come under three classes :

I. This class includes those apparent motions of the fixed stars and sun from which we learn the earth's motion and position (Chapters I, II, and III). Since the diurnal motion of the stars can be seen on any clear night, there is no difficulty in bringing together the observation and book study (Chapter II) of the subject. But it takes a longer time to see the slow annual motion of the stars treated of in Chapter III. If, however, a student has (as before recomrr.ended) paused between Chapters I and II to learn the constellations thoroughly, and has then studied Chapter II in the book and in nature, he will perceive by the time he reaches Chapter III some degree of that change in the position of the groups which is described in Articles 24 and 25, and the teacher has but to call his attention to it for illustration. It is not necessary to anticipate by telling him something of the motion in advance. If he has known the groups, he will remember their position, and can see afterward that it is changed. Since the whole year's motion is but a continuance or repetition of such changes, and also closely resembles the diurnal motion, which he has previously studied, such

MAP I.

For Study of the Stars from January aoth to April aoth.

URSA

MAJOR*

LEO MAJOR

HYDRA

ARGO NAVIS

GEMINI

CANIS MINOR

PERSEUS^

ECLIPTIC

ANDROMEDA •

ORION

CETUS

ERIOANUS

SCALE OF MAGNITUDES

' 2 3 4 5

THE HEAVENS

AS SEEN

CAUTION.— Bs sure to read the directions for using these maps, given in the Introduction page 3.

December 22d at midnight, January aoth at ten o'clock,

February 4th at nine o'clock, February igth at eight o'clock

MAP II.

For Study of the Stars from July 22d to October azd.

SCALE OF MAGNITUDES

* * • • •

' 2 3 4 5