The young astronomer; or, The facts developed by modern astronomy, collected for the use of schools and the general reader

Preface

Most treatises upon Astronomy contain much which is quite unintelligible to those who have not passed through a regular course of mathematical studies. It is, however, very desirable that all the youth in our schools should be familiar with those simple yet sublime facts, which have been developed by this science. To present these facts in language which can be comprehended by every good understanding in our common schools and academies, is the object of this work. It is hoped that these pages may incite a deeper interest in the study of this most noble of all the sciences ; that it may disseminate widely, in the popular mind, an acquaintance with those truths which are so eminently calculated to elevate the understanding, and to ennoble the heart ; and that many may be induced to prosecute the study into those higher regions of mathematical inquiries, which can call into requisition all the energies of a Newton and a Herschel.

Chapter I. General View Of The Solar System. — The Sun

General view of the Solar System — The Ptolemaic theory — The Copernican theory — The Planets, how distinguished — Comets — Proportionate magnitudes of the Planets — The Sun, its constitution ; probably inhabited — Rotation of the Sun ; revolution in its orbit — Spots on the surface of the Sun — Face of the Sun — Eclipse of the Sun — Distance from the Earth — Mode of ascertaining its distance — Influence of the Sun's rays — Arguments in favor of the Sun being inhabited,

Chapter II. The Planets — Mercury — Venus — The Earth

Primary Planets — Secondary Planets — Mercury, its distance from the Sun ; its size — The population Mercury could sustain — Length of a year upon Mercury — Length of a day — Atmosphere of Mercury — Venus, its distance from the Sun — Size of Venus — The diurnal and annual revolution of Venus — The mountains and atmosphere of this planet — Satellites — The population Venus could sustain — The Earth ; its size ; its revolutions ; its form ; its orbit — The Equinoxes — Population of the Earth- Latitude — Longitude — Mode of ascertaining latitude and longitude, 24

VI CONTENTS.

Chapter III. The Moon — Mars

Distance of the Moon from the Earth ; its size ; its revolutions ; its surface — Volcanoes in the Moon — The Moon's atmosphere — Eclipses of the Moon — Supposed influence of the Moon upon the weather, diseases, &c. — Is the Moon inhabited ? — The tides — Mars, its distance ; rapidity of its motion — The diurnal and annual revolution of Mars, 40

Chapter IV. Vesta — Astrea — Juno — Ceres — Pallas — Jupiter

The Asteroids ; how discovered ; place of their orbits ; theory respecting them — Vesta ; its size ; period of its revolution ; when discovered — Astrea ; when discovered ; its distance from the Sun — Juno ; its size ; the population it could sustain ; period of its revolution ; its atmosphere— Ceres ; its size ; extent of surface ; population it could sustain ; its atmosphere ; its revolutions — Pallas ; its supposed size — Meteoric stones, how accounted for — The atmospheric hypothesis — The volcanic hypothesis — The lunar hypothesis — The nebular hypothesis — The planetary hypothesis — Jupiter ; its year ; its day ; its distance from the Sun ; its magnitude ; its equable temperature ; its atmosphere — The belts of Jupiter — The moons of Jupiter — Eclipses of Jupiter's satellites ; scenery, . . . .52

Chapter V. Saturn Herschel, Or Uranus

Saturn ; its distance from the Sun ; its magnitude ; its diurnal annual revolution — Satellites of Saturn — Rings of Saturn — Magnitude of Saturn's rings — Character of the rings — Probably inhabited — Herschel ; by whom discovered ; its distance from the Sun ; its magnitude ; its probable temperature — Satellites of Herschel — Possible population of all the planets — Magnitude of the Sun, 65

CONTENTS. Vll

Chapter VI

Comets ; their physical constitution — Newton's opinion — Size of Comets ; their number ; their periodic revolutions ; the purposes they are intended to subserve — Newton's opinion — Nature of their light, 75

Chapter VII. The Fixed Stars

Fixed Stars; their number — Constellations — Magnitude of the Stars — Sirius — Vega — Classification of Stars — Variety in the structure of the Stars — Color of the Stars — Distance of the Stars — New Stars and lost Stars — Opinions of Mrs. Sommerville, La Place and Dr. Good — Variable Stars — Theories to account for Variable Stars — Double Stars — Colored Suns — Triple and multiple Stars — Our Firmament, 82

Chapter VIII. Observation

Difficulties under which Astronomical discoveries and investigations are made — Appearance of the heavens to an observer on the Earth — Apparent motions of the Stars — The meridian — Importance of this line — Effect of the position of the observer on the apparent motions of the heavenly bodies — Apparent motions of the Sun and Stars at the equator ; at the poles ; at intermediate positions — Altitude — Latitude — Ferguson's instrument — Simple observations which may be made by the pupil, 105

Chapter IX. Instruments And Observatories

Exactness necessary in Astronomical observations — Royal Observatory at Greenwich — The telescope — Principle of its construction — Reflecting telescopes — Herschel's great telescope— The Rosse telescope — Difficulties in manufacturing large specula — Annealing — Loss of Light — Lenses — Experiment to illustrate their refracting powers — Achromatic lenses — Difficulties in using a telescope — Tremors — Adjustments — State of the atmosphere — The finder — Interesting objects to be viewed — Transit instruments — Clock — Equatorial instruments, .117

Vlll CONTENTS.

Chapter X. Practical Results

Uses of Astronomy in Navigation — Instruments used by Navigators — The quadrant — The sextant — Observations made on board ship at noon — Mode of obtaining the Latitude — Longitude — Relation of longitude to time — Illustrations of this — Signal made at Greenwich to give the ships in the port of London their time — Lunar observations, and design of them — Singular phenomenon in respect to the length of the day at sea — Advantages fvhich have resulted to mankind from the science of Astron- «iy, . 132

THE

YOUNG ASTRONOMER.

Chapter I. General View Of The Solar System

THE SUN.

The science of Astronomy treats of the motions, magnitudes and distances of the heavenly bodies. From the earliest ages of the world the stars have attracted attention ; and shepherds on the hillside, as they watched their flocks by night, and philosophers, on their housetops, have observed their apparent motions, counted their numbers, and endeavored to arrange them into classes or fanciful groups, which they called Constellations.

The theory of Astronomy which has almost universally prevailed until within the last four hundred years, is called the Ptolemaic theory. It receives this name from Ptolemy, its most distinguished advocate. Ptolemy lived about two hundred years after the birth

Of what does Astronomy treat ? How long has Astronomy engaged attention ? Who have particularly watched the stars ? What are groups of stars called ? What theory of Astronomy has formerly prevailed ? Why is the Ptolemaic theory so called ? When did Ptolemy live ? 1* of Christ. The Ptolemaic theory of Astronomy places the Earth in the centre of the universe, and supposes the Sun and the stars to revolve around it.

The theory now universally received, is called the Copernican theory. Copernicus, who established this theory, lived about four hundred years ago. The Copernican theory is, that the Sun is the centre, around which the Earth, and all the planets of the Solar system revolve. It also supposes that the fixed stars are suns and centres, around which other systems revolve.

The Solar system includes the Sun, and all the heavenly bodies which revolve around it. Those bodies which, revolving around the Sun, shine, not by their own, but by reflected light, are called planets. The innumerable other glittering bodies which twinkle in the firmament, and which are immovable in their relative position, and which shine not by reflected, but by their own light, are called fixed stars. The planets can be usually distinguished from the fixed stars by their mild, moon-like light, while the stars shine with a more intense and twinkling lustre. The planets are supposed to be worlds, somewhat resembling our own. The fixed stars are considered as suns. They are at such an immense distance, that even the telescope does not reveal to our view the revolving worlds to which they dispense light and heat.

What is the Ptolemaic theory ? What is the present theory of Astronomy called ? Who established this theory ? When did he live ? What is the Copernican theory ? What does the Solar system include ? What are planets ? What are fixed stars ? How can the planets be distinguished ? How can the stars be distinguished ? What are the planets supposed to be ? What are the stars supposed to be ? Why do we not see the planets which are supposed to revolve around the stars ?

GENERAL VIEW OF THE SOLAR SYSTEM. 11

There are connected with the Solar system, besides the planets, vast bodies, called comets, of whose physical structure and constitution, comparatively little is known. They pass around the Sun, and then disappear in the depths of space, and after the lapse, perhaps, of many centuries, reappear, alarming the ignorant by their portentous aspect in the sky. It has been supposed that the comets may connect two or more systems together, by revolving around the suns which are the centres of those systems.

It is difficult from diagrams to attain any very correct conception of the Solar system. The following striking illustration, of the proportionate magnitudes and distances of the bodies composing the Solar system, has been given by Herschel. Let the Sun be represented by a globe two feet in diameter. At eightytwo feet distant put down a grain of mustard seed, and you have the size and place of the planet Mercury. At the distance of one hundred and forty-two feet lay down a pea, and it will represent Venus. Two hundred and fifteen feet from the central globe place another pea of about the same size, and.it will represent the Earth. At the distance of three hundred and

What bodies besides planets are connected with the Solar system ? What is said of their physical structure and constitution ? After passing around the Sun where do they go ? What has it been supposed that comets connect ? Do diagrams give a correct idea of the Solar system ? Who has given a striking illustration of the bodies composing this system ? By what would Herschel represent the Sun ? At what distance would he place Mercury ? What would represent its proportionate magnitude ? At what distance would he place Venus ? What would represent the proportionate magnitude of Venus ? At what distance would he place the Earth ? What would represent the proportionate magnitude of the Earth ?

THE YOUNG ASTRONOMER.

twenty-seven feet place a pin's head, and it will represent the planet Mars. About five hundred feet from the Sun, place five of the smallest grains of sand, to represent Vesta, Astrea, Juno, Ceres and Pallas, which are called the Asteroids. At a quarter of a mile from the globe which represents the Sun, place an orange of a middle size, and it will represent Jupiter. An orange a little smaller, two-fifths of a mile distant, will represent Saturn. And Herschel would be represented by a cherry, three quarters of a mile distant. It will at once be perceived that by or-

COMPARATIVE MAGNITUDES OF THE PLANETS.

By what would Mars be represented ! At what distance ? Where would the Asteroids be placed ? By what would they be represented ? At what distance should Jupiter be placed ? By what should it be represented ? Where should Saturn be placed ? What would represent its size ? What would represent the size of Herschel ? At what distance should it be placed ?

GENERAL VIEW OF THE SOLAR SYSTEM.

dinary orreries and diagrams, but a feeble idea can be communicated of the comparative magnitude and distances of the worlds which compose the Solar system. The accompanying diagram may, however, give the reader a general idea of the relative position of the planets, and may perhaps aid the mind in forming correct conceptions.

RELATIVE POSITION OF THE PLANETS.

iglSfihfil

THE SOLAR SYSTEM.

THE SUN.

The Sun is the centre of the Solar system. For many ages that vast luminary was supposed to be a globe of liquid fire. But now the body of the Sun is ascertained to be a solid and dark mass, of stupendous magnitude; somewhat resembling in its aspect the globe on which we live. A luminous atmosphere, many distinguished Astronomers have conjectured, of vast extent, and of intense brilliancy, surrounds the solid body of the Sun, and throws out its rays of light and heat to the most distant of the planetary worlds. In this atmosphere of dazzling splendor, there are frequently seen openings or cavities, through which is distinctly visible the dark mass of the interior globe. It is impossible to ascertain what is the precise nature of this luminous substance, of such intense energy, which envelopes the Sun. Many have supposed it to be analogous to the electric fluid which gleams from the thunder clouds ; and that vast accumulations of this subtle and inexplicable element surround the Sun. These electric clouds, or luminous vapors, are supposed, by Herschel, to be between two and three thousand

What body is the centre of the Solar system ? What was the Sun formerly supposed to be ? What is the Sun now ascertained to be ? From whence does the light and heat of the Sun proceed ? What is frequently seen in this atmosphere ? What is the precise nature of this luminous substance ? To what have many supposed it to be analogous ? How thick are these luminous clouds ?

miles in thickness. This discovery of modern science beautifully illustrates the Mosaic account of the creation. It is there said that light was created before the Sun itself. This now appears reasonable. For light or this luminous atmosphere was first created. The Sun was then appointed the great light-bearer , around which the luminous substance was gathered. Thus has the advancement of science removed a difficulty in the account of the creation, which in the days of ignorance perplexed the mind.

The cavities which are seen in these luminous clouds, appear like dark spots on the surface of the Sun. Some are found to be of the most enormous magnitude. The smallest which are visible to us, are not less than five hundred miles in diameter. Some have been ascertained to be more than forty thousand miles in length, and sixteen thousand in breadth. Upon such a spot as this, ten globes, as large as the earth, might be placed. These spots never continue for a long time of the same figure ; but are subject to numerous and rapid changes. It is seldom that any one spot continues for more than six weeks. The luminous clouds seem to close together, and as one spot disappears, others are seen in other places. Some occurrences seem to lead to the opinion that when there are many spots observed

What does the discovery of these luminous clouds illustrate ? What difficulty has appeared in the Mosaic account of the creation ? How does this discovery remove the difficulty ? How do the cavities in these luminous clouds appear ? Are they large or small ? What is the size of the smallest ? What is the size of the largest ? What illustration is given of the size of this largest cavity ? How long do these spots generally continue ? Describe the mode of their change ? What opinion has been drawn respecting the influence of these spots upon temperature ?

on the surface of the Sun, the heat of the Sun is diminished. But upon this subject not enough facts have yet been collected to lead to any positive conclusion.

Beneath this atmosphere of such ineffable splendor, and between it and the sun, there is observed to be a second atmosphere, or stratum of clouds, of inferior brightness. It is supposed that this cloudy stratum is intended as a screen, to protect the inhabitants of the Sun from the too excessive light and heat of the electric or luminous atmosphere which surrounds that stupendous globe. Thus there may be a happy population rejoicing in the valleys and along the hillsides of that magnificent mansion of our God. They may enjoy the luxury of an ever genial clime. They may dwell in attempered rays of heat and light, which never dazzle and never burn.

The magnitude of the Sun surpasses all powers of human conception. The Sun is about nine hundred thousand miles in diameter. It is three millions of miles in circumference. But these vast numbers convey no distinct conception to the human mind. The imagination may, perhaps, be slightly aided by the following illustrations of the Sun's magnitude.

1. Were the Sun placed where the Earth now is, its solid contents would fill the whole space enclosed by the orbit of the Moon ; and it would extend two hun-

Why is there no positive conclusion upon this subject ? What is interposed between these luminous clouds and the surface of the Sun ? What is supposed to be the object of this screen ? What inference is drawn from this fact ? What is the diameter of the Sun ? Do these numbers convey any distinct idea to the mind ? How may the imagination be aided ? What is the first illustration of the magnitude of the Sun ?

dred thousand miles in every direction beyond the orbit of the Moon. The whole of this almost measureless region would be filled with the solid contents of that stupendous orb.

2. Were a person to travel over thirty square miles of the Sun every day, it would require more than two hundred and twenty millions of years to survey its surface.

3. Were the Sun a hollow ball, it would contain thirteen hundred thousand globes as large as the Earth.

4. If the surface of the Sun were peopled with inhabitants, it would sustain as large a population as could live on eight hundred and fifty thousand such globes as the Earth.

Notwithstanding these illustrations, the mind in vain endeavors to attain a conception of the grandeur of this majestic globe. Even angelic powers may be exhausted in the endeavor to grasp the grand idea. It is considered as a demonstrated truth, that the surface of the Sun is diversified with towering mountains and widespread vales. And upon these hillsides and verdant savannahs, where no night ever darkens the sky, and no winter ever chills the flowers or the fruit, there may be beauty and luxuriance of vegetation, such as Eden never witnessed. There is probably no night upon the Sun, for it is enveloped, at all times, in a blaze of splendor. There is probably no winter upon the Sun, for that atmosphere, which is the fountain of heat,

What is the second illustration of the magnitude of the Sun ? What the third ? What the fourth ? How is the surface of the Sun diversified ? Is there any night upon the Sun ? Why not ? Is there any winter there ? Why not ?

exists equally at the equator and at the poles. May we not hope that a sinless population crowds those blissful vales. If there the clamor of selfishness and of oppression is unknown, and every heart throbs with love for God, and love for its fellow, surely this realm, in all its amplitude, is worthy to be ranked among those heavenly mansions, which our Saviour has gone to prepare for his followers. As one star differeth from another star in glory, and as there are different degrees of rank and elevation among the intelligences whom God has formed, it is by no means improbable that the Sun may be peopled by a loftier race than man; by a race unsusceptible of fatigue, and living in the vigor of eternal youth. It is one of the peculiarities of the future home of redeemed man, that " there is no night there. 55

The Sun has a revolution upon its own axis. It revolves once in about twenty-five days. This rotation was discovered by the motion of spots on the surface or disk of the Sun. A dark spot will frequently appear on the eastern edge of the Sun, and move gradually along, day after day, till it arrives at the western edge. Then disappearing, in the course of about twelve days it will again be seen manifesting itself upon the eastern edge. The regular rotation of these spots, proves that the Sun is a globe ; and that it revolves upon its own axis from east to west, in about

What pleasing hope may we indulge ? What supposition is not improbable ? What motion has the Sun ? In what time does the Sun revolve upon its axis ? How was this rotation discovered ? Describe the movement of these spots ? What does the regular rotation of these spots prove ?

THE SOLAR SYSTEM.

twenty-five days. The Sun is eclipsed when the Moon, passing between the Earth and the Sun, casts its shadow on the Earth, as is seen in the accompanying diagram.

Besides the revolution of the Sun upon its own axis, Herschel conjectures that the Sun, carrying with it all the planetary system, is circling around some distant and unknown centre. What that centre is no one can tell. In what depths of space it is buried, no one can imagine. But the idea is sublime in the highest degree, that the stupendous Sun itself, with all its retinue of revolving worlds, is gliding through the depths of space in an immeasurable orbit. Probably thousands of years are occupied, in traversing this limitless pathway. Herschel was led to this conjecture, by observing that the stars, in one quarter of the heavens, appear to be very gradually approaching each other, while in an opposite.quarter the stars as gradually seem to recede. This apparent motion, almost imperceptible as it is, would be caused by an actual movement of the Sun towards the stars, which seem to be receding from each other.

When is the Sun eclipsed ? What motion has the Sun besides a revolution upon its axis ? What is the centre around which the Sun revolves ? What length of time is probably occupied by the Sun in traversing its circuit ? What led Herschel to the conclusion that the Sun revolves around some distant centre ? What would cause the stars apparently to recede from each other ?

The distance of the Sun from the Earth is estimated to be ninety-five millions of miles. A carriage, traveling at the rate of twenty miles an hour, would occupy more than five hundred years in traversing this distance. Many persons are incredulous, respecting the ability of Astronomers to measure the vast distances interposed between the heavenly bodies and the Earth. But the principles upon which this measurement is conducted are perfectly simple, and the results demonstrably accurate. Any civil engineer can measure the height of a distant mountain, or a fortress, though he may not be able to climb the mountain, and the fortress may be inaccessible. He simply measures a, base line, upon the ground on which he stands. From the two extremities of this line, he takes the bearing of the object ; that is the angle which a line running to the distant object makes with the base line. Then from the most simple principles of geometry and arithmetic, he calculates the distance of the object. It is in this way that most of the surveys on Earth are taken. Neither the magnitude nor the distance of the object under observation increases the difficulty of the measurement. *

In measuring the distance of the heavenly bodies, we take for a base line the diameter of the Earth, which is eight thousand miles. And when the distance

What is the distance of the Sun from the Earth ? How long would it take a carriage to traverse this distance at the rate of twenty miles an hour ? What is said of the accuracy of astronomical measurements ? How does a civil engineer measure heights which are inaccessible ? What does not add to the difficulty of measurement ? In measuring the distance of heavenly bodies what is taken as the base line ? What is the diameter of the Earth ?

of the object observed is such that even that vast line dwindles, as it were, into a point, we take for a base line the diameter of the Earth's orbit. This line is nearly two hundred millions of miles in length. To pass over it, in a rail-car travelling at the rate of thirty miles an hour, would require nearly eight thousand years. The more distant the object is, the larger, of course, is the angle of its bearing with the base line. If the object be so distant that there is no perceptible angle at all, of its bearing with the base line, the distance of the object cannot be measured. Under such circumstances, it is certain that the object cannot be within certain limits, but its positive distance cannot be ascertained. And such is the fact in reference to nearly all the stars glittering in the firmament. With so stupendous a base line as the diameter of the Earth's orbit, no perceptible change in their bearing can be perceived from either extremity.

The Earth is farther from the Sun when in one part of its orbit than when in another part. This results from the fact that the orbit in which the Earth revolves is not a perfect circle. Its diameter in one direction is more than three millions of miles longer than in the

When the diameter of the Earth is not sufficient what is taken ? What is the length of the diameter of the Earth's orbit ? How long would it take a carriage, at the rate of thirty miles an hour, to pass over this line ? What influence has the distance of an object upon the angle of its bearing with a base line ? When can the distance of an object not be measured ? What is certain in such a case ? What is the fact in reference to the fixed stars generally ? With what base line is it endeavored to measure their distance ? Is the Earth always equally distant from the Sun ? Why is it not always equally near the Sun ? How much difference is there in the diameters of its orbits ?

other. Such a figure is called an ellipse. The difference between the longest and the shortest diameter is called the eccentricity of the ellipse. The Earth is nearest the Sun in winter, and farthest from it in summer. In summer, however, the rays of the Sun fall nearly perpendicularly upon us, causing intense heat. In the winter the rays fall upon us obliquely, and hence the severity of the cold.

Almost every motion which takes place on the surface of the Earth is influenced by the rays of the Sun.

1. All winds are caused by the heat of the Sun promoting currents of air in the atmosphere. Particles of air heated intensely in one place by the rays of the Sun, rapidly rise, while the surrounding atmosphere rushes in to fill the vacant space. Hence gentle zephyrs, tornadoes and whirlwinds.

2. The whole vegetable kingdom is dependent for life and growth upon the light and heat of the Sun's rays.

3. The heat of the Sun raises, by evaporation, the water of the ocean, circulates it in vapor over the land, and then letting it fall in showers, creates all the springs and rivers.

4. The crumbling of the mountains even is caused by the abrasion of the wind and rain, and the change of the seasons which the Sun produces.

What is such a figure called ? What is meant by the eccentricity of an ellipse ? When is the Earth nearest the Sun ? When farthest from it ? Why have we intense heat in summer ? Why cold in winter ? By what are most of the motions which take place on the surface of the Earth influenced ? How are winds caused ? How does the heat of the Sun promote currents in the atmosphere ? Upon what does the vegetable kingdom depend ? How are springs and rivers caused ? How is the crumbling of mountains caused.

It has long been a question ©f much interest, whether the Sun is probably inhabited. Upon this question Astronomers are not yet fully agreed. The following arguments have been adduced by the most eminent Astronomers, in favor of the Sun being peopled. They are sufficient to lead most minds to the conclusion that probably countless myriads of happy beings are rejoicing amid the splendor of that vast orb.

1. The Sun is evidently a solid globe of mountains and valleys, and thus adapted to be the home of intelligent creatures.

2. It is contrary to analogy to suppose that God, who fills every drop of water with animal life, would create so magnificent and beautiful a world, and leave it to solitude and desolation.

3. There is evidence that beneath the luminous clouds which surround the Sun, there is an inner atmosphere, which seems to be carefully prepared as a veil, to screen the inhabitants of the Sun from too excessive heat.