Part 1

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POPULAR

LESSONS IN ASTRONOMY,

ON A NEW PLAN;

IN

WHICH SOME OF THE LEADING PRINCIPLES OF THE SCIENCE ARE ILLUSTRATED BY ACTUAL COMPARISONS, INDEPENDENT OF THE USE OF NUMBERS.

BY

FRANCIS J. GRUND,

AUTHOR OF “AN ELEMENTARY TREATISE ON PLANE AND SOLID GEOMETRY,” “ELEMENTS OF NATURAL PHILOSOPHY AND CHEMISTRY,” &c.

BOSTON

CARTER, HENDEE AND CO.

1833.

ENTERED according to Act of Congress, in the year 1833, By FRANCIS J. GRUND, in the Clerk’s office of the District Court of Massachusetts.

I. R. BUTTS, SCHOOL STREET.

NOTICE.

The Geographical Miles, which are used in the scales and tables of this book, are _German Geographical Miles_, of which 15 make one degree. The teacher or pupil may easily change them into _English Geographical_ Miles, by multiplying them by 4, the square miles by 16, and the cubic miles by 64.

PREFACE.

Although many elementary works on Astronomy are already before the public, yet it is believed there is none in which the various magnitudes, surfaces, and distances of the heavenly bodies, are presented to the eye of the learner by actual comparisons;—the only way, perhaps, in which young pupils can be expected to form a correct idea of them. This the author has attempted in the following pages. The comparative diameters, surfaces and distances of the different planets, are all drawn, in the plates, according to a fixed scale of geographical miles; the surfaces of the planets are actually reduced to square measure, and drawn in proportion to each other and the sun; so that the youngest pupil, by a mere glance of the eye, is enabled to form a correct idea of their respective magnitudes. A similar plan has been pursued, in regard to the division of the Earth into Zones, and with respect to the extent of the five great Continents of our Globe. The Appendix contains an exposition of the population of America, Europe, Asia, Africa, and Australia, accompanied by a plate for the illustration of the comparative settlements on those Continents.

_Boston, June 24, 1833._

POPULAR LESSONS IN ASTRONOMY.

LESSON I.

THE EARTH IN ITS RELATION TO THE SUN, MOON AND STARS.

§ 1. The Earth on which we live, and on which plants, trees and animals successively live and die, is only a small part of the world; it is but one of the smallest bodies in the Universe. To the world belong yet the _Sun_ from which we receive warmth and light, the _Moon_, and an innumerable class of bodies, which, at night, appear to us as so many points of light. These are called _Stars_.

The reason why the Stars appear to us so small, is because they are so far from us; and things appear smaller in proportion as they are farther removed from us. This you will have noticed, when looking from a high steeple on the people below, or on a vessel far out in the harbour, or on a chain of mountains at a great distance.

§ 2. Most all Stars appear to us, every night in the same position; they seem actually to be _fixed_ in the heavens; and for this reason they are called _fixed Stars_. There are however Ten others, of which it has been ascertained _that they move regularly round the Sun in large circles_. These are called _Planets_ or _wandering Stars_.—The fixed Stars are supposed to be similar to the Sun, in as much as they are bodies which have their own light. The Planets, on the contrary, are of themselves dark bodies, and receive, like our Earth, light and warmth from the Sun. We see them only in consequence of the solar light which they _reflect_ from their surfaces, and this is the reason why they appear to us as bright as the other Stars.

§ 3. The discoveries of Philosophers have proved beyond a doubt, _that our Earth itself is one of those Planets_, which move round the Sun in stupendous large circles, whose grandeur is hardly conceived by the most powerful imagination. _Our Earth, therefore, is, itself, a Wandering Star_, and the line in which it moves round the Sun is called its _Way_ or _Orbit_.

§ 4. The Planets, together with our Earth keep each a certain fixed distance from the Sun. On this account they do not disturb each other in their orbits. But they vary from each other in magnitude; although all of them (consequently also our Earth) have a _round_ shape, similar to a ball.

In former times men believed that the Earth was flat, or a circular plate on all sides surrounded by water. But this is not true. For it has been proved by a great many observations and actual measurements, that the Earth has a spherical (ball-like) form. Moreover there are navigators who have actually _sailed round the world_, and who have noticed the fact that at sea, the tops of distant objects are seen sooner than the rest; which again proves the spherical form of our Earth. For an illustration you may look at the adjoining plate Plate No. I.

The man who is represented as standing on a portion of our Earth, will at first only see the topmast of a vessel at sea; when she comes nearer his eye will discover a much greater portion of her; but when in the third position every part of the vessel will be visible.

§ 5. Some of the Planets are, in their motion round the Sun, _accompanied by other dark bodies_, which, like the Planets themselves, receive light and heat from the Sun. These are called _Satellites_ or _Moons_. Such a Satellite is the _Moon which accompanies our Earth_; and there are Planets (as we shall see hereafter) which have Four and Six, and One that has even Seven Moons.

§ 6. Besides the Planets and Moons there is yet another class of bodies, moving round the Sun in exceedingly long ovals. They are but seldom visible, and are distinguished from other heavenly bodies by a tail which is often three, four, and more times larger than the body itself. These are called _Comets_; but their number has not, as yet, been precisely ascertained.

§ 7. The Planets, Moons and Comets, together with the Sun around which they move, form what is called our _Solar System_. But what will you say, if you are told that each fixed Star in the firmament is a Sun which, like our’s, has its Planets and satellites and Comets; in short, that each fixed Star is the centre of a solar system, a thousand and more times larger than our own!! But how infinitely great must God’s Creation appear to us, when we reflect that all these globes, as well as our own, may be inhabited by reasonable beings!!!

RECAPITULATION OF LESSON I.

[If the pupil has learned and understood this lesson, it may perhaps be not unreasonable to suppose he will like to know something more about the Planets and the Moons in our system. But the teacher ought not to allow him to enter upon the second lesson, before he has recapitulated the first.]

QUESTIONS.

[§ 1.] Does the Earth, or the globe on which we live, comprise the whole world which God has created? Is our Earth any considerable portion of the Universe? What other bodies belong to it? Why do the Stars appear to us so small?

[§ 2.] Do all the Stars which we see remain in the same position? What are those called which remain _fixed_? What, those, which are moving regularly round the Sun? What are the fixed Stars supposed to be? Have the Planets any light of their own? From what body do the Planets receive their light?

[§ 3.] What important discoveries have Philosophers made respecting the nature of our Earth?

What is the line in which our Earth moves round the Sun, called?

[§ 4.] Why do the orbits of the different Planets not disturb each other? Are all Planets of the same magnitude? What is their shape? What is the shape of our Earth? What reason have you to believe, that the Earth is round? Explain Plate I?

[§ 5.] By what are some Planets in their motion round the Sun accompanied? What are the bodies which accompany them called? What body accompanies our Earth in its motion round the Sun? Are there Planets which have more than One Moon?

[§ 6.] What other class of bodies is there, besides the Planets and the Moons? Are these bodies always visible? By what are these bodies distinguished? What are they called?

[§ 7.] What do the Planets, Moons and Comets, together with the Sun, round which they move, form? What is each fixed Star supposed to be?

LESSON II.

OF THE PLANETS AND THEIR RELATIVE POSITION WITH REGARD TO THE SUN AND EACH OTHER.

§ 8. The Planets of which we have spoken in the First Lesson are Eleven in number, of which each has received a proper name. They are in the order in which they are placed from the Sun, the following:

Mercury. Venus. The Earth. Mars. Vesta. Juno. Ceres. Pallas. Jupiter. Saturn. Herschel.

The adjoining diagram, on Plate No. II, may serve for an illustration. You will see from it, that the Earth is the third Planet from the Sun. Mercury and Venus come before it; the most remote from the Sun is _Herschel_, so called from the astronomer’s name, who has but lately discovered it.

§ 9. The Earth is constantly attended by One Satellite (Lesson I, § 5); Jupiter by Four (see the diagram), Saturn by Six, and Herschel by Seven. Saturn is, besides, constantly surrounded by a broad luminous ring, which distinguishes it from all other Planets, and of which we shall speak hereafter.

§ 10. With regard to the magnitude of the different Planets it has been observed that although some of them are much larger than Our Earth; yet in Comparison to the Sun they are but small bodies, as you may see from the figures on plate No. III, in which the different Planets are drawn in proportion to the Sun: you will perceive from it;

1. That the Sun is a great many times[1] larger than either of the Planets.

2. That the Sun is much larger than all the Planets (our Earth included) taken together.

3. That Jupiter is the greatest Planet in our solar system.

4. That Saturn is the second Planet with regard to magnitude.

5. That Herschel ranks third.

6. That the Earth ranks fourth; but that

7. Each of the other Planets and the Moon are smaller than the Earth.

8. That either of the Planets Ceres, Vesta, Juno, Pallas is smaller than the Moon.

§ 11. If you cut a ball or a sphere in halves, and through the centre of one of the flat surfaces, draw a straight line across the whole surface, then this line is called the _Diameter_ of the ball or sphere.—Now as the Sun and the Planets are nothing else but large balls or spheres (Lesson I, § 4), we may also speak of their Diameters.—Thus we say, “the Diameter of the Sun is so many times larger than that of the Earth; the Diameter of Jupiter is so many times larger than that of Venus,” etc.

You will now easily understand what the straight line means, which, in plate No. III is drawn through the centre of the circle, which represents the Sun; also the straight lines which are drawn through the circles which represent the Planets.—You will also perceive from the first figure on plate No. III, that the Sun’s Diameter is larger than the Diameters of all the Planets taken together.

§ 12. Plate No. IV represents the _surfaces_ of the Planets, compared to that of the Sun.—For you must know that it is possible to _measure_ the surface of a sphere; which is done by supposing it to be spread out, and then seeing how many square inches, feet or yards it contains. This we have supposed to be done with the surfaces of the Sun and Planets, and accordingly, have drawn their square measurements, in Plate No. IV. in proportion to each other.

You will see from this Plate:

1. That the square-Contents of the Sun’s surface is greater than that of the surfaces of all the Planets taken together.

2. That the square-Contents of the Earth’s surface is nearly as large as that of the surfaces of Mercury and Venus taken together.

3. That the square-Contents of the surfaces of Vesta, Ceres, Juno and Pallas, taken together, is not yet sufficient to cover the surface of our Earth.

4. That the square-Contents of Jupiter’s surface is larger than that of the surface of any other Planet.

5. That the square-Contents of Jupiter’s surface is greater than that of the surfaces of all other Planets taken together.

6. That Saturn’s surface is the next largest.

7. That Herschel’s is still larger than those of our Earth, Venus and Mercury taken together.

8. That the square-Contents of the Moon is nearly as large as that of the surfaces of Ceres, Vesta and Juno, taken together; and that it is larger than that of Pallas’ surface taken alone.

In order that you may be better able to compare, you will find on Plate No. V

1. The surfaces of the different Planets, all drawn upon the Sun’s surface; from which you may see, how much larger the Sun’s surface is than the surfaces of all the Planets and the Moon taken together.

2. The surface of the Earth compared to that of Mercury and Venus.

3. The Earth’s surface compared to that of the Four Asteroids Pallas, Ceres, Juno and Vesta.

4. Jupiter’s surface compared to those of all the other Planets.

5. The square-Contents of the Moon compared to the surfaces of Vesta, Juno and Ceres.

6. Herschel’s square-Contents compared to that of our Earth, Venus and Mercury taken together.

§ 13. The Four Planets, Ceres, Vesta, Juno, and Pallas, are so small in proportion to the other Planets, and are so near each other (they are almost at the same distance from the Sun—see Plate II) that many distinguished philosophers are of opinion, they are but the fragments of One large Planet, which, from some cause or other, has _burst_.—But this is no subject for us now to inquire into;—we will therefore proceed to describe in the next lesson, the motion of the different Planets round the Sun.

RECAPITULATION OF LESSON II.

QUESTIONS.

[§ 8.] What are the names of the Eleven Planets _in the order in which they are placed from the Sun_? How many Planets are there between the Earth and the Sun? How many Planets come after our Earth? In what order then, is our Earth placed among the Planets? (Is it the first, second, etc. from the Sun)?

[§ 9.] How many satellites accompany our Earth? What is it called? How many satellites or Moons has Jupiter? How many has Saturn? How many has Herschel? By what is Saturn particularly distinguished from all other Planets?

[§ 10.] Are all Planets of the same magnitude as our Earth? Are the Planets in comparison to the Sun large or small bodies?—Is the Sun much larger than any of the Planets? Is the Sun larger or smaller than all the Planets, including our Earth, taken together? Which is the greatest of all Planets? Which Planet ranks, in magnitude, next to Jupiter? Which of the Planets ranks third in magnitude? Which, Fourth? What Planets are smaller than our Earth? What Planets are smaller than the Moon?

[§ 11.] What do you call the _Diameter_ of a ball or sphere? Is the Diameter of the Sun larger or smaller than the Diameters of all the Planets taken together?

The teacher may yet ask a number of questions respecting the Diameters of the Planets, which the pupil will be able to answer by looking on Plate III. He may, for instance, ask whether the Diameter of the Earth is larger or smaller than that of Venus? Whether the Diameter of Jupiter or Saturn is the largest, etc.? This will oblige the pupil to _compare_ the different magnitudes of the Planets and their Diameters.

[§ 12.] What proportion does the square-Contents of the Sun’s surface bear to that of the surfaces of all the Planets? What two Planets have together a surface nearly as large as that of our Earth? Are the surfaces of Ceres, Vesta, Juno and Pallas taken together sufficient or not, to cover the surface of our Earth? What Planets, therefore, could be covered with the Earth’s surface? Which Planet has the largest surface? What do you observe with regard to the square-Contents of Jupiter’s surface? and that of the surfaces of all other Planets, taken together? What Planet’s surface comes next in magnitude to Jupiter’s? What Planet’s surface is larger than that of our Earth, Venus and Mercury taken together? What three Planets’ surfaces taken together are smaller than that of the Moon? What Planet has nearly as large a surface as the Moon?

[§ 13.] What is the opinion of philosophers respecting the Four Planets, Ceres, Vesta, Juno and Pallas?

FOOTNOTES:

[1] Numbers are purposely omitted here, because abstract numbers convey little or no ideas to young pupils. Those who wish these relations expressed in numbers will find them in Table I at the end of the book.

LESSON III.

EXPLAINING THE MOTION OF THE PLANETS AND COMETS ROUND THE SUN.

§ 14. You have learned, in the preceding lesson, that the Earth and the other Planets are regularly moving round the Sun; but you must know that the time which each requires to complete a whole revolution, that is, the time which each needs to move once round, cannot be the same with all; as you may easily judge yourself: for the Planets which are next to the Sun will, of course, have a much smaller journey to perform, than those which are further from it. Thus Mercury, which is the first Planet in order from the Sun, will naturally come round much sooner than Jupiter, which is placed at a much greater distance from it.

That you may the easier understand this, the following Plate, No. VI, will represent to you our Solar System:

The Sun from which proceeds all light and heat, is placed in the centre. Then come the Planets Mercury and Venus; Third in order is our Earth with its Satellite the Moon; and so on. The rest of the Planets in the same order in which they are represented on Plate II. You will also perceive there the orbs of two Comets, distinguished as you were told, by a tail of light. The Planets Jupiter, Saturn and Herschel are each represented with their Moons, and the Planet Saturn with its luminous ring.

Now you will easily understand that Ceres, Vesta, Juno, Pallas, Mars, Jupiter, Saturn and Herschel, have each a much greater distance to travel, than our Earth; but that, on the contrary, Venus and Mercury can complete their revolution in a much shorter time.[2]

§ 15. The time which our Earth needs to travel once completely round the Sun, (to finish one revolution) is called a _Year_. Such a year has three hundred and Sixtyfive days;—and each of these days has again Twentyfour hours.

You see from this that the revolution of the Earth round the Sun gives us _a means of measuring time_, by which we are able to bring order and regularity into our business and transactions of life. For the making of clocks and watches is but a late invention, and we should be left entirely in the dark as regards the history of former ages, and a great many people would, at this present moment, be incapable of forming a correct estimate of time, if Providence had not given to all this appropriate means of measuring it.

§ 16. While the Earth needs a whole year for one revolution round the Sun; Mercury requires but Eightyone days, and Venus only about two thirds of One of our years. Mars, on the contrary, needs for one of his revolutions almost Two years; Vesta almost Four; Juno, Ceres and Pallas over Four years; Jupiter almost Twelve, Saturn over Twentynine, and Herschel nearly Eightyfour of our years![3]—And if these Planets, as we have reason to believe, are inhabited by beings endowed with human understanding and faculties, numbering their years as we do ours—by the revolution of their Planets round the Sun—how different from ours must be the Period of their existence!!

§ 17. During the time that the Earth is performing her journey round the Sun, the Moon, our constant attendant, is continually moving round the Earth, _and completes one of these revolutions in little more than Twentyseven days_.—Very important and interesting to us are the changes in appearance which she exhibits during each of these revolutions.—You probably will know, that the Moon does not appear to us, at all times, the same. Sometimes she is hardly at all visible, (at least not with the naked eye); at other times only a small rim of her is seen, which by degrees becomes larger and larger, until finally she appears in her full round form. After this she begins again to diminish, changes again into a small luminous rim, and finally disappears entirely from our sight. These successive changes in the Moon’s appearance are called _the Moon’s Phases_, or the _waxing and waning of the Moon_. The time during which the Moon is not seen is called _New Moon_; the time during which she exhibits her full shape is called the _Full Moon_; and the different periods of her waxing and waning (when she appears to us in the form of a crescent) are called _Quarters_. Thus we speak of the _First_ and of the _Last_ Quarter of the Moon. The First Quarter takes place after New Moon; the last Quarter after Full Moon.

The following diagram, Plate No. VII, may serve to represent to you the Moon’s phases as seen from our Earth.

When the Moon is in _a_, then the light of the Sun falls just on that side of it which is turned from the Earth. It is then, we have New Moon. When in _b_, a small brim of the Moon is seen, because a small portion of its lighted surface is then turned towards the Earth.—When in _c_ half of her lighted surface is turned towards us, and we have the First Quarter. In _d_ a still greater portion of the Moon’s lighted surface is visible, and in _e_, we have Full Moon, because her whole lighted surface is then turned towards the Earth. In _f_ the moon commences to wane (to grow smaller,) and in _g_ the last quarter commences; finally, when passed through the point _h_, we have in _a_, again New Moon. For familiar illustration you may also take a white ivory ball, holding it before a lighted candle, which may take the place of the Sun. When the ball is in a straight line between your eye and the candle it will appear to you all dark; because the lighted part is then entirely turned toward the candle (away from you), and you have the same case which is represented to you in the diagram, when the Moon is in _a_. But if you move the ball a little to the right, you will perceive a streak of light, similar to the First Quarter represented in the Diagram, when the Moon is in _c_. If moved still farther to the right, so that the whole lighted part of the ball is seen, it will resemble the Full Moon; represented in the Diagram, when the Moon is in _e_.

§ 18. While the Moon is moving round the Earth, it often occurs that she is placed in a direct line between ourselves and the Sun. In this case a greater or less part of the Sun is concealed from us, which causes a diminution of light or a partial darkness on our Earth. This we call an _Eclipse of the Sun_. (Such an Eclipse took place in 1831, and you will probably have an opportunity of seeing many more). If, on the contrary, the Earth is placed in a direct line between the Sun and the Moon, then the Moon will be obscured by our Earth. This is called an _Eclipse of the Moon_. The following two figures on Plate No. VIII will serve for an illustration.

You will easily perceive from them that if the Moon (as represented in Figure I) is placed in a direct line between the Sun and ourselves, it must necessarily conceal from us part of that luminary; and in this state cast a _shade_ upon our Earth.

But if the _Earth_ is placed in a direct line between the Sun and the Moon, (as represented in Figure II), then the Moon will be much more obscured, because the Earth is much larger than the Moon, and will therefore cast a much greater shade upon her.