The geography of the heavens and classbook of astronomy

Front matter

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^HetelleththennmberoftheStars,andcalleththemallbytheiriiaines»

THE

Preface

The rapid progress of the science of astronomy, for the last, few years, has again rendered it necessary to revise the Geography of the Heavens — a work, the popularity of which is sufficiently proved by a sale of 250,000 copies. The editor has, therefore, availed himself of the occasion to make such improvements, both in the book and maps, as seemed to be demanded by the progress of the science, and the most approved methods of instruction. Among these improvements we may mention the following : —

1. The matter of the book has been thoroughly assorted ; the most important paragraphs being printed in large type, and numbered, as in most modern text-books ; while that which seemed in the main explanatory of the more important portions, is left in small print. By this means an agreeable variety is afforded to the eye, while the book is made to contain far more matter, and is, consequently, far more complete, than it could otherwise have been.

2. A new set of Questions has been prepared throughout. These are brief, topical and suggestive ; and numbered to answer to the paragraphs to which they relate.

3. A complete list of Telescopic Objects in each constellation has been inserted ; giving the Kight Ascension and Declination of each object ; with a brief description of it ; and easy landmarks and directions by which it may be found ; and references to telescopic views of the same in the new maps. The color and relative magnitude of the components of the double stars, are also given. These Telescopic Objects, compiled with great labor from Smyth's Cycle of Celestial Objects, will be found especially

IV PREFACE.

valuable to all institutions having an equatorial telescope Indeed, they greatly enhance the value of the work for all classes of students.

4. Several small constellations that were delineated on the maps, but were not described in former editions of the book, have been described, and their history given in the present edition.

5. The page of the book has been greatly enlarged, for the double purpose of printing more matter and in larger type ; and to afford scope for wood-cut illustrations. Of these, great numbers have been introduced into the second part of the work, adapting it, in this respect also, to the wants of both teacher and student.

6. Still further to illustrate the second part of the work, the first map of the atlas has been re-draw r n and re-engraved, so as to illustrate more and better than the old map.

7. Two entirely new maps have been introduced into the Atlas, containing views of eighty different celestial objects ; such as Double Stars, Clusters, Nebulae, Comets, &c. These are all referred to in the book, and in turn refer from the objects back to the page of the book where they are described. These maps and the corresponding descriptions in the book will be found not only extremely interesting, but of incalculable value to the student.

8. A chapter on the history, structure and use of Telescopes, Transit Instruments, &c, has been introduced — a subject which every student of astronomy should understand, but one to which no attention was given in the previous editions.

Such are some of the principal new features of the present edition^— larger type, new questions, telescopic objects, new maps, new matter, and numerous illustrations, making it the most perfect and complete text-book of astronomy ever offered to the American public.

H. Mattison

Few York, April, 1856.

C K T E N T S .

CHAPTER I. Constellations on the meridian in November, H

HI.

IV.

V.

YI.

YH.

YIH.

IX.

X.

XI.

xn.

December,

January,

February,

March,

April,

May,

June,

July,

August,

September,

October,

Xni. Variable and Double Stars — Clusters and Nebulae, XIV. Via Lactea, or Milky- Way, ....

XV. Origin of the Constellations, ....

XVI. Number, Distances, and Economy of the Stars, XVII. Falling, or Shooting Stars, ....

Part II. -the Solar System

CHAPTER I. General Phenomena of the Solar System, History, &c, .

" II. The Sun — His Distance, Magnitude, &c, ....

" III. The Primary Planets — Mercury, Venus, &c, .... 11 IV. The Moon — Her Distance, Motions, Phases, &c,

11 V. Solar and Lunar Eclipses,

" YI. Primary Planets continued — Mars and the Asteroids,

" YII. Primary Planets — Jupiier and Saturn,

" VHI. Primary Planets — Uranus and Neptune,

w IX. Comets — Their Nature, Motions, Orbits, &c, .... " X. Of the Forces by which the Planets are retained in their Orbits,

" XL Proper Motion of the Sun in Space,

*' XII. Precession of the Equinoxes — Obliquity of the Ecliptic, .

11 XIII. Philosophy of the Tides,

" XIV. The Seasons — Different Lengths of the Days and Nights,

" XV. The Harvest Moon, and Horizontal Moon, ....

11 XVI. Refraction and Twilight,

" XVII. Aurora Borealis and Parallax,

"XVIII. Practical Astronomy — Reflection and Refraction of Light,

" XIX. Refractors and Reflectors,

M XX. Problems and Tables, ...

FAfcfK

Index To The Constellations

PAGE

Andromeda 18

Anser et Velpecula .... 121

Argo Navis 62

Aquila 118

Aquarius 131

Auriga 49

Bootes 84

Camelopardalus 51

Cancer 64

Janes Venatici 83

Canis Major 59

Can is Minor 56

Capricornus 127

Cassiopeia 22

Centaurus ...... 88

Cepheus 25

Cetus 32

Columba 46

Coma Berenices 77

Corvus 78

Corona Australis 118

Corona Borealis 94

Crater 71

Cygnus 124

Delphinus 122

Draco 110

Eridanus 47

Equuleus 131

Gemini 53

Gloria Frederica 134

Hercules 103

PAGB

Hydra 71

Lacerta 134

Leo 66

Leo Minor 69

Lupus (The Wolf) .... 90

Lepus (The Hare) .... 45

Libra 91

Lynx 52

Lyra 112

Monoceros 53

Musca 32

Nocta 88

Ophiuchus 107

Orion 41

Pegasus 129

Perseus . . 35

Pisces 20

Pisces Australis 133

Sagittarius 116

Sagitta 121

Scutum Sobieski 116

Scorpio 100

Sceptrum Brandenburgium ... 49

Serpentarius vel Ophiuchus . . 107

Serpens 93

Sextans 70

Taurus 38

Taurus Poniatowski . . . .115

Telescopium Herschellii ... 53

Triangulse 31

Ursa Major 73

Ursa Minor . . . . . .96

Virgo 80

Introduction

1. Astronomy is the science of the heavenly bodies — the Sun, Moon, Planets, Comets, and Fixed Stars.

2. In entering upon this study, the phenomena of the heave us, as they appear on a clear evening, are the first objects that demand our attention. Our first step is to learn the names and positions of the heavenly bodies, so that we can identify, and distinguish them from each other.

In this manner they were observed and studied ages before books were written, and it was only after many careful and repeated observations, that systems and theories of Astronomy were formed. To the visible heavens, then, the attention of the pupil should be first directed, for it is only when he shall have become, in some measure, familiar with them, that he will be able to locate his Astronomical knowledge, or fully comprehend the terms of the science.

3. For the sake of convenient reference, the heavens were early divided into constellations, and particular names assigned to the constellations and to the stars wjiich they contain. A constellation may be defined to be a cluster or group of stars embraced in the outline of some figure. These figures are, in many cases, creations of the imagination ; but in others, the stars are in reality so arranged as to form figures which have some resemblance to the objects whose names have been assigned to them.

These divisions of the celestial sphere bear a striking analogy to the civil divisions of the globe. The constellations answer to states and kingdoms, the most brilliant clusters to towns and cities, and the number of stars in each, to their respective population. The pupil can trace the boundaries of any constellation, and name all its stars, one by one, as readily as he can trace the boundaries of a state, or name the towns and cities from a map of New England. In this sense, there may be truly said to be a Geography of the Heavens.

4. The stars are considered as forming, with reference to

1. What is Astronomy? 2. What first studied? First step ? 3. How are -the heavens divided, and why? What is a constellation? What of these figures? In what sense may there really be a " Geography of the heavens . ? " 4. How are the stars classified, as respects their magnitudes? What expedient for designating their places in the heavens?

their magnitudes, sixteen classes ; the brightest being called stars of the first magnitude, the next brightest, stars of the second magnitude, and so on to the sixth class, which consists of the smallest stars visible to the naked eye. The next ten classes are seen only through telescopes.

In order to be able to designate with precision their situations, imaginary circles have been considered as drawn in the heavens, most of which correspond to, and are in the same plane with, similar circles, supposed for similar purposes, to be drawn on the surface of the Earth.

5. In order to facilitate the study of Astronomy, artificial representations of the heavens, similar to those of the surface of the Earth, have been made. Thus, a Celestial Atlas, composed of several maps, accompanies this work. Before, however, proceeding to explain its use, it is necessary to make the pupil acquainted with the imaginary circles alluded to, called the Circles of the Sphere.

CIRCLES OF THE SPHERE.

6. The Axis of the Earth is an imaginary line, passing through its centre, north and south, about which its diurnal revolution is performed.

The Poles of the Earth are the extremities of its axis.

The Axis of the Heavens is the axis of the Earth produced both ways to the concave surface of the heavens.

The Poles of the Heavens are the extremities of their axis.

The Equator of the Earth is an imaginary great circle passing round the Earth, east and west, everywhere equally distant from the poles, and dividing it into northern and southern hemibpheres.

The Equator of the Heavens, or Equinoctial, is the great circle formed on the concave surface of the heavens, by producing the plane of the Earth's equator.

A plane is that which has surface but not thickness. The plane of a circle is that imaginary superficies which is bounded by the circle.

7. The Rational Horizon is an imaginary great circle, whose plane, passing through the centre of the Earth, divides the heavens into two hemispheres, of which the upper one is called the

5. What helps to facilitate the study of the heavens? Circles? Called what? 6. Axis of the Earth? Poles? Axis of the heavens? Poles of the heavens? Equator of the Earth? Equator of the heavens, or Equinoctial? 7. Rational horizon? Sensible or apparent?

CIRCLES OF THE SPHERE. 11

visible hemisphere, and the lower one, the invisible hemisphere. It is the plane of this circle which determines the rising and setting of the heavenly bodies.

The Sensible or Apparent LIorizGn, is the circle which terminates our view, where the Earth and sky appear to meet.

To a person standing on a plain, this circle is but a few miles in diameter. If the eye be elevated five feet, the radius of the sensible horizon will be less than two miles and three quarters; if the eye be elevated six feet, it will be just three miles. The observer being always in the centre of the sensible horizon, it will move as he moves, and enlarge or contract, as his station is elevated or depressed.

8. The Poles of the Horizon are two points, of which the one is directly overhead, and is called the Zenith ; the other is directly underfoot, and is called the Nadir.

Vertical Circles are circles drawn through the Zenith and Nadir of any place, cutting the horizon at right angles.

The Prime Vertical is that which passes through the east and west points of the horizon.

9. The Ecliptic is the plane of the Earth's orbit ; or the great circle which the Sun appears to describe annually among the stars. It crosses the Equinoctial, a little obliquely, in two opposite points, which are called the Equinoxes. The Sun rises in one of these points on the 21st of March ; this point is called the Vernal Equinox. It sets in the opposite point on the 23d of September ; this point is called the Autumnal Equinox. One half of the Ecliptic lies on the north side of the Equinoctial, the other half on the south side, making an angle with it of 23^-°. This angle is called the obliquity of the Ecliptic. The axis of the Ecliptic makes the same angle with the axis of the heavens; so that the poles of each are 23-J- apart.

This angle is perpetually decreasing. At the commencement of the Christian era, it was about 23' 45'. At the beginning of 1836, it was only 23* 27' 38", showing an annual diminution of about half a second, or 45".70 in a hundred years. A time will arrive, however, when this angle, having reached its minimum, will again increase in the same ratio that it had before diminished, and thus it will continue to oscillate at long periods, between certain limits, which are said to be comprised within the space of 20° 42'.

10. The Ecliptic, like every other circle, contains 360°, and it iri divided into 12 equal arcs of 30° each, called signs, which the ancients distinguished by particular names. This division commences at the vernal equinox, and is continued eastwardly round to the same point again in the following order : Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capri-

8. Poles of the horizon? Vertical circles? Prime Vertical? 9. Ecliptic? Equinoxes? How is the Ecliptic situated with respect to the Equinoctial? Obliquity of Ecliptic? Is this angle permanent? 10. How is the Ecliptic divided? Where cn^iuu-nced, and how reckoned? Name signs in order? How does the Sun proceed t\" ..g:i the signs?

l* c&rmbSj Aquarius, Pisces. The Sun, commencing at the first degree of Aries, about the 21st of March, passes, at a mean rate, through one sign every month.

11. The Zodiac is a zone or girdle, about 16 degrees in breadth, extending quite round the heavens, and including all the heavenly bodies within 8° on each side of the ecliptic. It includes, also, the orbits of all the planets, except some of the asteroids, since they are never seen beyond 8° either north or south of the ecliptic.

12. Parallels of Latitude are small circles imagined to be drawn on the Earth's surface, north and south of the equator, and parallel to it.

Parallels of Declination are small circles, imagined to be drawn on the concave surface of the heavens, north and south of the equinoctial, and parallel to it ; or they may be considered as circles formed by producing the parallels of latitude to the heavens.

13. The Tropic of Cancer is a small circle, which lies 23£° north of the Equinoctial, and parallel to it. The Tropic of Capricorn is a small circle, which lies 23|-° south of the Equinoctial, and parallel to it. On the celestial sphere, these two circles mark the limits of the Sun's farthest declination, north and south. On the terrestrial sphere, they divide the torrid from the two temperate zones. That point in the ecliptic which touches the tropic of Cancer, is called the Summer Solstice ; and that point in the ecliptic which touches the tropic of Capricorn, is called the Winter Solstice.

The distance of these two points from the equinoctial, is always equal to the obliquity of the ecliptic, which, in round numbers, is 23c° ; but, as we have seen, the obliquity of the ecliptic is continually changing; therefore the position of the tropics must make a correspondent change.

14. The Coheres are two great circles which pass through the poles of the heavens, dividing the ecliptic into four equal parts, and mark the seasons of the year. One of them passes through the equinoxes at Aries and Libra, and is thence called the Equinoctial Colure; the other passes through the solstitial points or the points of the Sun's greatest declination north and south, and is thence called the Solstitial Colure.

The Sun is in the equinoctial points the 21st of March and the 23d of September. He is in the solstitial points the 22d of June and the 22d of December.

15. The Polar Circles are two small circles, each about 66£°

11. What is the Zodiac? 12. Parallels of latitude? Of declination? 13. The tropics? Cancer? Capricorn? What do these circles mark in the celestial sphere? Ol ' " terrestrial ? 14. The Colures ? Where situated ? When is the Sun at the equinocti^.. , -ts? The solsticial? 15. What are the Polar Circles?

CIRCLES OF THE SPHERE. 13

from the equator, being always at the same distance from the poles that the tropics are from the equator. The northern is called the Arctic circle, and the southern the Antarctic circle.

16. Meridians are imaginary great circles drawn through the poles of the world, cutting the equator and the equinoctial at right angles.

Every place on the Earth, and every corresponding point in the heavens, is considered as having a meridian passing through it; although astronomers apply but 24 to the heavens, thus dividing the whole concave surface into 24 sections, each 15° in width. These meridians mark the space which the heavenly bodies appear to describe, every hour, for the 24 hours of the day. They are thence sometimes denominated Hour Circles.

In measuring distances and determining positions on the Earth, the equator and some fixed meridian, as that of Greenwich, contain the primary starting points ; in the heavens these points are in the ecliptic, the equinoctial, and that great meridian which passes through the first point of Aries, called the equinoctial colure.

. IT. Latitude on the Earth, is distance north or south of the equator, and is measured on the meridian.

Latitude in the Heavens, is distance north or south of the ecliptic, and at right angles with it.

Longitude on the Earth, is distance either east or west from some fixed meridian, measured on the equator.

Longitude in the Heavens, is distance east from the first point of Aries, measured on the ecliptic.

18. Declination is the distance of a heavenly body either north or south of the equinoctial, measured on a meridian.

Right Ascension is the distance of a heavenly body east from the first point of Aries, measured on the equinoctial.

It is more convenient to describe the situation of the heavenly bodies by their decli • nation and right ascension, than by their latitude and longitude, since the former corresponds to terrestrial latitude and longitude.

Latitude and declination may extend 90° and no more. Terrestrial longitude may extend 130° either east or west; but celestial longitude and right ascension, being reckoned in only one direction, extend entirely round the circle, or 360°.

It is easy to convert ripht ascension into time, or time into right ascension, for if a heavenly body is one hou. in passing over 15°, it will be one fifteenth of an hour, or four minutes, in passing over 1\

If the first point of Aries be on the meridian at 12 o'clock, the next hour line, whicr. Is 15° E. of it, will come to the meridian at 1 o'clock; the second hour line at 2 o'clock ; the third at 3, £c. Of any two bodies whose right ascensions are given, that one will pass the meridian first which has the least right ascension.

19. Iii consequence of the Earth's motion eastward in its orbit, the stars seem to have a motion westward, besides their apparent diurnal motion caused by the Earth's revolution on its axis ; so that they rise and set sooner every succeeding day by about four minutes, than they did on the preceding. This is

16. Meridians? How many? What other name? How measure distances on the earth 9 tn the heavens? IT. What is latitude on the earth? In the heavens? Longitude on the earth? In the heavens? IS. Declination? Right ascension Why describe by T). and R. A.? Extent of latitude? Declination? Longitude and R, A ? How convert R. A. into time? Which of two bodies given will first pass the meridian? 19. What apparent motion of stars? Cause? Results?

called their daily acceleration. It amounts to just two hours a month. On this account we have not always the same constellations visible to us throughout the year. While some, that were not visible before, are successively rising to view in the east, and ascending to the meridian, others sink beneath the western horizon, and are seen no more, until, having passed through the lower hemisphere, they again reaopear in the east.

DESCRIPTION AND USE OP THE MAPS.

20. The first map of the atlas represents, upon a large scale, 9 general view of the solar system. This will be more fully described in the second part of the work.

The next six maps represent different sections of the concave surface of the heavens. The first of these exhibits the principal constellations visible to us in October, November, and December ; the second, those visible in January, February, and March ; the third, those visible in April, May, and June ; and the fourth, those visible in July, August, and September ; with the exception," however, of the constellations which lie beyond the 50th degree of north and south declination, of which, indeed, those around the North Pole are always, and those around the South Pole, never visible to us.

21. These constellations are represented on the sixth and seventh maps, called circumpolar maps, which are an exact continuation of the others, and if joined to them at their corresponding degrees of right ascension and declination, they might be considered as constituting one map. The scale on which all the above-mentioned maps are drawn is that of a 16-inch globe. The lines drawn on the maps have been already defined ; and their use, being nearly the same with those in geography, will be readily understood. Those which are drawn from right to left, on each side of the equinoctial and parallel to it, are called Parallels of Declination. Those which are drawn up and down through the maps, at intervals of 1 5°, are called Meridians of Right Ascension, or Hour Circles.

The scale at the top ^nd bottom of the first four maps, and in the circumference of the circumpolar maps, indicates the daily progress of the stars in right ascension, and shows on what day of the month any star will be on the meridian at 9 o'clock in the evening.

20. What said of maps? First? Next six? 21. Sixth and seventh? Scale? Describe lines? Scale indicates what?

CLASSIFICATION OF STARS, NEBLJUE, ETC. 15

22. The first four maps t)f the heavens are so constructed that the pupil in using them must suppose himself to face the south, and to hold them directly overhead in such manner that the top of the map shall be towards the north, and the bottom towards the south ; the right hand side of the map will then be west, and the left-hand east. In using the circumpolar maps he must suppose himself to face the pole, and to hold them in such a manner that the day of the given month shall be uppermost.

The constellation called the Great Bear is an exception to this rule ; in this constellation the principal stars are marked in the order of their right ascension.

That point of projection for the maps which would exhibit each successive portion of the heavens directly overhead at 9 o'clock in the evening, was chosen, because in summer at an earlier hour the twilight would bedim our observation of the stars, and at other seasons of the year it is easier to look up to stars that want an hour of their meridian altitude than to those which are directly overhead.

CLASSIFICATION OF STARS, NEBULA, &c.

23. For purposes of convenience in finding or referring to particular stars, recourse is had to a variety of artificial methods of classification. First, the whole concave of the heavens is divided into sections or groups of stars, of greater or less extent, called Constellations. — (Of the origin of these figures see page 143). Next, they are classified according to their magnitudes, (as already stated art. 4), and designated on the maps accordingly. Thirdly, the stars of each constellation are classified according to their magnitudes in relation to each other, and without reference to other constellations. Thus, for instance, the largest star in Taurus is marked a, Alpha ; the next largest /3, Beta; the next, y, Gamma, &c, till the Greek alphabet is exhausted. Then the Roman (or English) is taken up, and finally, if necessary, recourse is had to figures.

This useful method of designating particular stars by the use of the Ore ek and Roman alphabet, was invented by John Bayer, of Augsburg, in Germany, in 1603. It has been adopted by all succeeding astronomers, and extended by the addition of the Arabic notation 1, 2, 3, &c, wherever the stars in a constellation outnumber both alphabets.

As Greek letters so frequently occur in catalogues and maps of the stars and on the celestial globes, the Greek alphabet is here introduced for the use of those who are unacquainted with it. The capitals are seldom used for designating the stars, but are here given for the sake of regularity.

22. How use the first four maps of the heavens? Circumpolar? What exception? What point of projection chosen, and why? 23. Classification or designation of stars ? By whom invented, and when?

THE GREEK ALPHABET.

A a

Alpha

N

V

Nu

B

P

Beta

A

Xi r

Gamma

Omicron

A

Delta n

Pi

E e

Epsilon p

Kho

Z f

Zeta c

Sigma

H

V

Eta'

T

T

Tau

Theta

T

V

Upsilon

I

L

Iota

4>

Phi

K

K

Kappa

X

X

Chi

A

X

Lambda

Psi

M p

Mu

Q u

Omega

24. As a further aid in finding particular stars, and especially in determining their number, and detecting changes, should any occur, catalogues of the stars have been constructed, one of which is over two thousand years old. Several of the principal stars have specific names, like the planets, as Sirius, Aldebaran, Regwlus, &c.

25. The stars are still further distinguished, as single, double, triple, multiple, binary, variable, new, and nebulous.

A single star is one that appears as a unit under the most powerful telescopes. Double, triple, and multiple stars, are those that appear single to the naked eye, but by the aid of telescopes are found to consist of two or more stars. Binary stars are double stars revolving around each other, often called Binary Systems. Variable stars are those that are found to undergo certain fluctuations in their brightness, sometimes becoming quite invisible. In most cases these changes are periodical and regular, on which account they are called Periodical stars. New stars are those that suddenly blaze forth in some portion of the heavens previously void. Nebulous stars are those which are surrounded by a faint nebula, or halo of light or mist.

26. A cluster of stars is an assemblage or group, thrown promiscuously together, like the Pleiades and Hyades in Taurus, and the Bee Hive in Cancer. A Nebula is a cluster so remote as to appear only like a faint cloud or haze of light. Resolvable Nebula, are those that can be resolved into distinct stars by the aid of a telescope. Irresolvable Nebulce are those that have not

24. What further aid? Age? Names of stars? 25. Stars, how further distinguished? Single stars? Double, &c? Binary? What other name? Variable stars? What other name and why? Newstars? Nebulous? 26. What are clusters ? Nebu- Ise? Resolvable Nebulas? Irresolvable ? Annular? Planetary?

CLASSIFICATION OF STARS, NEBULvE, ETC. 17

as yet been thus resolved. Annular Nebula are those that have the form of an annulus or ring. Planetary Nebula are those that resemble planets in form, and in the sharpness of their outline. Stellar Nebula are those with a star in the centre, the same as nebulous stars, already described (25).

A more detailed account of the double stars, clusters and nebulae, will be given after the student has become somewhat familiar with the constellations.

27. We may now imagine the pupil ready to begin the study of the visible heavens. The first thing of importance is to fix upon the proper starting point. This, on many accounts, would seem to be the jSTorth Polar Star. Its position is apparently the same every hour of the night throughout the year, while the other stars are continually moving. Many of the stars also in that region of the skies never set, so that when the sky is clear, they may be seen at any hour of the night. They revolve about the pole in small circles, and never disappear below the horizon.

On this account they are said to be within the circle of perpetual apparition. On the other hand, the identity of the North Polar Star, strange as it may appear, is not so easily determined by those who are just entering upon this study, as that of some others. For this reason, the point directly overhead, called the zenith, is preferable, since upon this point every one can fix with certainty in whatever latitude he may be. It will be alike to ail the central point of the visible heavens, and to it the pupil will learn imperceptibly to refer the bearing, motion, and distances of tne heavenly bodies.