Astronomical geography

Preface

Va,

TEXT BOOK on PHYSICAL GEOGRAPHY

has long been needed, specially adapted to advanced classes in our common schools.

It is the intention of the author to write such a text book on Physical Geography, but owing to the lack of means the first section, Astronomical Geography, now goes before the public asking my co-workers in the field of education to support me in carrying out the grand scheme of lifting our common schools to a higher plane of usefulness. In an experience of five years the author has found that our present system of Physical Geographies, written for high schools and colleges, are not adapted to the wants of our common schools. To meet these requirements and to encourage deeper investigation into the broad field of science, I place this little volume before the teachers of our country .

The author holds himself responsible for any error? that may have crept into the work ; but if any such there be, he

4 (PREFACE.

will feel under lasting obligations to those who will communicate the same to him. The work is the result of experience and patient toil, but if it supplies the demands for which it was written, the author will feel greatly rewarded for his work . SAMUEL M. SARK.

Circleville O., August 22, 1887.

u VI

Introduction

LESSON I.

i. Derivation. — The word, geography, is derived from the Greek ge, the earth, and graphein, to write. Its literal signification is, therefore, a description of the earth.

2. Sphere of Geography. ■ — Strictly speaking, geography includes both an account of those changes which have been wrought by man, and those which have been produced by Nature. It treats not only of the earth, but of all things related to the earth . In its broadest sense it includes Astronomy, Geology, Mineralogy, Zcology, Meteorology, Phys_ ics, Botany, and various other sciences . Hence we see, that instead of geography being a distinct science, it is a collection of various sciences.

3. Classification. — There are two-logical divisions of geography, political and physical.

Political Geography treats of the earth as the dwelling place of man ; of the society he has organized to promote his own welfare ; of the government he has originated to suppress his crimes ; of the religion he has invented to reverence a Supreme Being ; of his manner of living etc.

Physical Geography describes the extent and explains the cause of the various natural phenomena of the earth.

4. Physical Geography is subdivided into astronomical, physiographical, meteorological, zoological and botanical geography.

5 . Astronomical Geography is the science which considers the earth in its relation to the Universe, and in its relation to the Solar System .

6. Physiographical Geography treats of the land and water belonging to the earth .

7. Meteorological Geography is the science of the atmosphere and its phenomena.

8 . Zoological Geography treats of animals and their distribution over the earth.

9. Botanical Geography treats of the plants and their distribution.

10. Mathematical Definitions — (a) A point has position but no dimensions.

(b) A line is a magnitude which has length, but no volume.

(c) A straight line is one that does not change its direction throughout.

(d) A curve line is one that changes its direction at every point.

(e) Parallel lines are those, which, lying in the same plane, would never meet ; no matter how far they be produced.

(£) An angle is the parting of two lines which meet, (g) The point where the lines meet is called the vertex, (h) An angle is named from a letter placed at its vertex as in fig. i, which reads, the angle E or the angle F E G.

Fig. 1.

(i) The size of an angle depends entirely upon the difference in direction of its sides and not at all upon the length of those sides.

(j) A right angle is one formed by a straight line meeting another straight line making the adjacent angles equaL The first line is then said to be perpendicular to the second.

(k) An obtuse angle is greater than a right angle.

(1) An acute angle is less than a right angle.

Fig. 2.

(m) In fig. 2, A D E and E D B are right angles. A D C is an acute angle . C D B is an obtuse angle.

(n) A convex surface is one that bulges out in a spherical form, like the outside of an egg shell.

(o) A concave surface curves in, like the inside of an egg shell-

(p) A plane has length and breadth without thickness.

(q) A circle is a plane bounded by a curve line, every point of which is equally distant from a point within called the center,

(r) The circumference of a circle is the line which bounds it.

(s) A straight line drawn from one side of the circle to the other, passing through the center is called the diameter.

(t) A straight line drawn from center to circumference is called the radius.

(u) The circumference of a circle is divided into 360 equal parts called degrees .

(v) An angle is measured by the number of degrees in the arc that subtends it .

(w) An Ellipse is a plane figure, bounded by a curve line, every point of which is at such distances from two points within, called its foci, that the sum of these distances is in each case the same.

(x) The center of an ellipse is the point midway between the foci.

(y) The Major Axis is the longest diameter.

(aa) The Minor Axis is the shortest diameter.

In x c\

Fig. 3.

(bb) Fig. 3 represents an ellipse.

O and X are the foci.

D C is the major axis.

A B is the minor axis .

(cc) A solid has length, breadth, and thickness.

(dd) A Sphere is a volume bounded by a curved surface, every point of which is equally distant from a point within called the center.

The diameter of a sphere is a straight line passing from one side, through the center, to the other side.

(ee) The Axis of a revolving sphere is the diameter around which it turns.

The ends of the axis are called the poles.

(ff) An Oblate Spheroid is a sphere flattened at the poles like an orange.

(gg) A Prolate Spheroid is a sphere elongated at the poles like a lemon.

, SECTION

LEbSON II.

1, The Universe is the name applied to the entire material world.

There are truths before which man becomes humiliated and perplexed, although, he knows from the very nature of things, the absolute necessity of their existence. Among such are the eternal duration of time and the infinity of space. We live, therefore, in an expanse without limits, in whose bosom the universe is floating.

2. Constituents of the Universe. — The first persons who studied the heavenly bodies fancied the Earth standing in the center of a hollow sphere ; that the stars were golden nails, which,seen on the concave surface, the great Architect of the universe had used in its construction.

Modern science teaches us that the universe is composed of Nebulae, Stars, Planets, Satellites, Comets and Meteors.

These bodies are divided into luminous and non-luminous bodies. Luminous bodies shine by their own light. Non luminous bodies shine by reflecting light of the luminous bodies.

n ASTRONOMICAL GEOGRAPHY.

3. Nebulae — It has long been a subject of debate whether there existed a nebulous fluid in space. When the spectroscope was invented it forever ended the controversy. The nebulae (nebula, a cloud) are masses of glowing gas, probably, Hidrogen and Nitrogen.

The light of some of the nebulae, is subjected to great variations.

They are separated from us by such enormous distances that light, wiiich travels at the enormous rate t 86,000 miles per second, requires many thousand years to reach us from some whose existence is revealed by the telescope . Many parts of the heavens having a nebulous appearance, contain no nebulae ; but the glowing mass consists of many stars, apparently, near each other, but doubtless, this appearance is due to the inconceivable distances they are apart from us ; and they are in reality as widely separated from each other, as the stars of our own Milky Way. Nearly all of the nebulae lie far beyond our stellar universe.

4. Stars. — Stars are huge balls of matter, which, floating in the depth of space, give us light because they are white hot. They are visible during the night, and are known by their twinkling ; but during the day their light is extinguished by the presence of the greater light of one glorious star, the Sun, whose rays light up and warm the earth. The stars are moving rapidly through space, al-

"though, they are apparently at rest on account of the great distances they are from us.

The Sun appears to be the largest and brightest star in the firmament. This is because that orb is comparatively near ois. The apparent feebleness of the stars is due to the great ■distances they are separated from us; the nearest being more than 200,000 times more distant than the sun.

Some stars are much larger and brighter than the sun . As the land surveyor measurer, the distance across a river which he cannot cross, so, too, the astronomer spans the enormous distances from star to star.

Alpha Centauri is the nearest star, the Sun excepted. It is about 20,000,000,000,000 miles away. This is a truth which in our minds can form no conception. Yet this distance is small when compared with the distances of the stars of the 1 2th magnitude made visible by the telescope ; for it only takes light about three and a half years to reach us from Apha Centauri ; while if a star of the 12th magnitude would be at this moment destroyed, the inhabitants of the earth would continue to see it for 3,500 years. That is, it takes the light of these distant luminaries 3,500 years to reach us.

A cannon ball taking the earth as its starting point, traveling at the rate of 1,320 feet per second^ would not arrive at Alpha Centauri in less than 2,500,000 years ; while a railroad train running at the rate of 40 miles per hour, would

H ASTRONOMICAL GEOGRAPHY.

arrive at that star in about 55,000,000 years. These distances are entirely to great for our conception, yet they are but mere points in boundless space.

5. The Magnitude of a star depends upon its relative brightness. The brightest stars are known as stars of the first magnitude ; while the most feeble visible to the naked eye, are of the sixth magnitude. There are about 20 stars of the first magnitude ; 65, of the second ; 200, of the third; 450, of fourth ; 1,100, of the fifth ; 4,000, of the sixth. The number increases largely in ascending the scale. From the above we see that the whole number of stars visible to the naked eye, is about 6,000.

Since we see but one-half of the sky, the greatest number visible at a time, is about 3,000. With a powerful telescope about 20,0c 0,000 stars between the first and sixteenth magnitude, inclusive, are visible.

Of this number more than 18,000,000 belong to our own stellar universe, the Milky Way.

6. Constellations. — The stars are arranged in groups called constellations and are usually named after a fabulous personage or some animal w 7 hich the relative position of the stars suggested to the mythological mind.

7 Variations. — The light of some of the stars, as in the case of the nebulae, is subjected to variations which, so far as we now know r , occur in regular periods of time.

The cause of these variations is unknown, but three theories have been advanced which are worthy of attention.

First — It is believed that all parts of the star's photosphere, or surface, are not (equally luminous ; that it revolves upon its axis ; and, hence it is brightest when the brightest side is turned toward us, and darkest when the dark side meets our view.

Second — It is believed that the star has one or more non-luminous planets revolving around it ; that these planets get between us and the star forming either a total or partial ecilpse.

Third — It has been found that when a planet comes near the Sun it becomes brighter. Hence it is supposed that the variable has a large planet revolving around it ; and that that part of the star's photosphere nearest the planet will be brightest.

8. Color. — The light of most of the stars is white , but some are red, orange, blue, green, etc.

9. Constituents of the Stars. — We know but little of the elements of the stars ; however, we do know that their photospheres contain some elements known to us. Among the most widely diffused are Hidrogen, Sodium and Iron. The constituent elemets of the stars bear a striking resemblance to each other. It seems probable that each of these great luminaries has the same past history. At present, we are not prepared to conjecture about the future.

10. The Milky Way. — We have already spoken of star-clusters under the head of nebuhe . The sun, all of the stars visible to the naked eye, and millions of telescopic stars form one great star-cluster, known as the Milky Way. A ray of light traveling at the rate of 186,000 miles per second, starting at one side of the Milky Way, passing through the center, would reach the opposite side in about 15,00a years ! Then leaving the last star in our cluster it would continue at its usual velocity, for several millions of years,, through empty space and at last arrive at other star-clusters,, some of them exceeding our own Milky Way in vastness of extent and numbers. Thus we see that the visible star-clusters, numbering about 5,000, and isolated from each other by inconceivable distances, are only so many milky ways floating in the bosom of infinite space.

LESSON HI.

i. The Sol, ml System. — The Solar System is situated in the center of that portion of the universe known as the Milky Way.

2 . Constituents, The Solar System is composed of the sun, planets, satellites, comets, meteors and an apparent ring of nebulous matter called the Zodiacal Light.

3 . The Sun is the center of the Solar System. It holds all the other members of the system in their respective places by its attraction .

It supplies the planets with light and heat, and supports all animal and vegetable life on our globe .

If we examine the Sun with a *telescope, we notice dark spots on its photosphere. By observing these spots, it is known that it turns on its axis in about 27 days ; also that its axis is inclined to the plane of the ecliptic [See Chap. IV.] Since we know that the Sun rotates on its axis, and its disk is always a perfect circle, we conclude, therefore,that the Sun is a perfect sphere. The Sun is 852,584 miles in diameter, and it is nearly 1,300,000 times larger than the earth. Its weight, however, is only about 300,000 times as great.

The Sun is surrounded by a highly absorptive atmosphere which extends about 80,000 miles above its surface. In this atmosphere float incandescent clouds composed of vaporized metals and other constituent elements of a surface beneath. It is from these clouds whence the light so necessary to our existence is derived .

The Sun is a variable star with a period of 1 1 years.

We do not know what keeps up the Sun's great supply of light and heat, but we can theorize. A philosopher says, " One theory is good until a better one is given. "

The constant supply of light and heat is supposed to be produced by the contraction of its cooling mass.

Another theory is, that meteors are constantly falling into

*Do not look at the Sun with even the smallest telescope, without proper instruction and appliances, for it is very dangerous. Some astronomers have lost their eyes.

the sun from interplanetary space. They arrive at its surface with enormous velocity, and being suddenly stopped their motion will be converted into heat. This theory, however, is now generally discarded for the first . How long the Sun will continue to supply our system with light and heat is not known. Certainly it can not last forever if not replenished, and we have no evidence that such is the case. A body in giving out heat becomes cooler. Hence we conclude that the Sun at some time, cold and lonely, will go falling through infinite space. The ice will gradually creep from the poles to the equator on our own. terrestrial abode, and before its mighty tide man willdissappear from the face of the earth. Such we imagine will be the "end of the world . " Astronomers, however, have no evidence of any loss of heat for several hundred years. Should the sad spectacle above mentioned occur, it need not trouble us, for there is enough energy stored up in that radiant orb to supply us with light and heat for many thousand years . The Sun is not stationary but is moving through space towards the constellation of Hercules at the rate of 4 miles per second. Many astronomers think our Solar System is revolving around Alcyone, the brightest star of the Pleiades. Since the Sun carries with it ail of its attendants, we are constantly entering new realms of space.

Before leaving the Sun let us again glance at its vast extent in order to get it well impressed on our minds.

If the Sun were a hollow shell and the Earth placed at its center, there would not only be enough room for the Moon to revolve at its actual distance (240,000 miles,) around the Earth, but each part of its orbit would still be nearly 200, 000 miles below the surface of the Sun. A railroad train traveling at the ordinary rate, would perform its journey around the Sun in about 30 years. We feel humiliated before its vast extent ; yet the Sun forms but a molecule of the luminous matter of the universe.

LESSON IV.

1. Planets. — A planet is a body that revolves around the Sun in an almost circular path.

2. The Orbit of a planet is the path in which it travels.

3. The planets are non-luminous bodies, and shine by reflecting the light of the Sun .

4. The planes in which the orbits of the planets lie do not coincide ; but nearly so.

5. The orbit of the Earth is called the Ecliptic.

6. The plane in which the orbit of the Earth lies is called the Plane of the Ecliptic.

7. Mercury. — Mercury is the nearest planet to the Sun whose existence is known. It may be seen in the West, just above the Sun, after that body has set, or after a certain time has elapsed, it may be seen in the morning before the Sun rises. Mercury is a little tinged with red and is the only planet that twinkles . Since its orbit is between us and the Sun it presents phases similar to the Moon. Its surface is rugged with mountains higher than those of the Earth. It has also evidences of a higher and denser atmosphere than our own. It revolves, around the Sun in a very eliptical orbit . When it is nearest the Sun it receives twice as much heat as when farthest away. It receives more than six times as much light and heat as our earth. Its mean distance from the Sun is about 35,000,000 miles ; its diameter 2960 miles ; its day 24 hs., 5 min., 30 sec. ; its year 88 of our days; the inclination on its axis, greater than that of the earth ; its seasons 22 days ; its volume }£ of the earth ; and its specific gravity about 7 ; that is, the average weight of its constituent parts is about 7 times greater than the weight of an equal bulk of water. Owing to the great eccentricity of its orbit and the inclination of its axis, its climate is subjected to great extremes. " Every 44 days on an average there is a change in temperature nearly equal to the difference between frozen quicksilver and melted lead-"

8. Venus. — Venus is the second planet from the Sun . Owing to its comparative nearness, it appears the largest and brightest planet. It is surrounded by a transparent atmosphere in which float the clouds that rise from its stormy

ASTRONOMICAL GEOGRAPHY. Zl

sea, presenting the same spetacle to us, we see every day on the Earth,

It rotates on its axis in 23 hrs. 21 min. Its inclination to a perpendicular to the plane of its orbit is very great, (49 58') and it is, therefore, like Mercury subjected to great extremes of temperature.

It revolves around the Sun in 224^ of our days, which is the length of its year. Its mountains are higher than those of the Earth.

Its mean distance from the Sun is about 66,000,000 miles, its diameter is 7,510 miles ; its specific gravity about five and one-fifth; its volume about four-fifths of the Earth. It receives twice as much light and heat as the Earth. Venus being between us and the Sun, it presents phases similar to Mercury. The phases of both planets, however, are not visible to the naked e\e.

Venus may be seen in the evening in a certain part of the year. It is then known as the Evening Star. After an elapse of a few months it may be seen in the morning before the Sun rises. It is then known as the Morning Star.

The planets we have already considered, are called inferior planets ; those which lie outside of the Earth's orbit are called superior planets.

9. Mars — Passing the Earth to be dealt with hereafter, we come to Mars the fourth planet in order from the Sun . Its day is about the same length of ours ; its year about 687 of our days; its diameter 4920 miles ; its inclination of its axis about the same as the Earth, and, hence, its seasons about the same.

Mars has land, water, snow, clouds and mists the same as the Earth. You remember the color of the setting Sun is red. This is due to the absorption of its light in our atmosphere. The color of Mars is of a fiery red. This is due to the absorption of a part of the Sun's light ; that is, the atmosphere of Mars acts as a sieve and stops all of the Sun's light but the red which it reflects to us.

A large white spot surrounds the south pole of Mars, and is supposed to consist of ice and snow. The orbit of Mars is very eccentric and the south pole being inclined towards the Sun when it is in that part of its orbit nearest the Sun, we would naturally expect the white spot to decrease during the planet's summer in its southern hemisphere. Now this is exactly what happens . Hence, the supposition that the white spot is a snow zone is very plausible. The mean distance of Mars from the Sun is about 139,000,000 miles.

LESSON V.

1. Jupiter. — Omitting the Asteroids of which we shall soon have something to say, we arrive at Jupiter, the largest planet of our system, and the fifth in order from the Sun.

It is 1,400 times larger than the Earth ; its mean distance from the Sun is about 476,000,000 miles ; the light and heat it receives from the Sun, but one-twenty-fifth as intense as that received by the Earth ; its day about 10 hrs., making it rotate so rapidly that a point on its equator travels about 27 times faster tnan one on the Earth's equator. Owing to its very rapid rotation the flattening of its poles is very great, its equatorial diameter being one-sixteenth longer than its polar. The axis of Jupiter is only inclined 3 4' to a perpendicular to the plane of its orbit. Hence there is no perceptible change of seasons .

Its year is equal to about 12 of our years. Jupiter is nearly as brilliant as Venus, and is always in the Zodiac [Lesson XIII] which makes it easily recognized. Its specific gravity is about 1^, which makes it weigh 300 times as much as the Earth .

2. Saturn. — Saturn, the sixth planet in order from the Sun, is 734 times as large as the Earth. It rotates very rapidly on its axis ; its days being only 10% hours long. Its year is equal to about 29^ of our years ; the inclination of its equator to the plane of its orbit 26^°, and, hence its seasons are subjected to changes similar to those of the Earth ; its mean distance from the Sun is about 872,000,000 miles ; and its specific gravity only two-thirds.

Around Saturn, 20,000 miles above its equator, rises a huge flat ring. This ring is followed by a second and the

H

ASTRONOMICAL GEOGRAPHY.

second by a third. This system of multiple ring's is only about ioo miles thick but it is 160,000 miles in diameter and 38,000 miles broad.

The ring's are not stationary, but revolve around Satura with greater rapidity than the planet itself. Close observation has revealed that the rings are undergoing changes.

Fig. 4.— Saturn and its rings compared as to size with the Earth.

The general supposition is that these rings are composed of many little satellites, each moving independently in its own course around the planet, and being closely packed together, they present the appearance of bright rings.

3. Uranus. — The six planets already named were known to the ancients . The rest have been discovered in modern times .

In 1 78 1, Sir William Herschel discovered the seventh planet in order from the Sun, and it is called Uranus . It is just visible to the naked eye. Its year is equal to 84 of our years, but there being no spots on its surface, we are not able to tell its period of rotation. It is 72 times as large as the Earth ; its specific gravity is nearly 1. The mean distance from the Sun is 1,754,000,000 miles.

4. Neptunk — The discovery of Neptune is one of the grandest triumphs of modern science.

Every molecule of matter in the universe attracts every other molecule, and after taking all the known causes into account, there was still something that effected the motions of Uranus . This led to the belief that there was another planet beyond the orbit of this planet. Le Verrier, a French astronomer, proved by a mathematical calculation that there must be another planet beyond the orbit of Uranus, and wrote to Berlin observers, telling them where he imagined the planet to be . Following Le Verrier's directions, the planet was discovered the same evening. (September 1846.)

Like Uranus, Neptune's period of rotation is unknown ; its year is equal to 165 of our years ; its specific gravity nine-tenths, and its mean distance from the Sun is 2,746,000,000 miles.

The intensity of its light and heat is only about one-nine hundredth as great as that of the earth.

5. The Planets in General. — The eight planets already named in the order of their sizes are : Jupiter, Saturn, Neptune, Uranus, Earth, Venus, Mars and Mercury. On account of their large size they are called Major Planets, the remainder are very small and are called Minor Planets, or Planetoids.

LESSON VI.

1. The Asteroids — The Asteroids,or minor planets revolve around the Sun between the orbits of Mars and Jupiter. Their average distance from the Sun is about 260,000,000 miles. The discovery of the asteroids is due to what is known as Bode's Law. Let us write down o 3 6 12 24 48 96

and add 4 to each number ; we now have 4 7 10 16 28 52 100.

This series of numbers represents the distances of the ancient planets from the Sun . 4, represents Mercury ; 7,

Venus ; 10, Earth ; 16, Mars ; 28, ; 52, Jupiter ;

an 100, Saturn. 28 has apparently no planet to represent. Kepler boldly placed an undiscovered planet in the gap, but up to the discovery of Uranus the suspected planet had not revealed itself. When, however, this planet was discovered, and it was found that the next number in . Bode's series, 196, would represent its distance, a society of astronomers was formed, and search made for it.

On Jan. 1, 180G, Ceres was discovered which filled up the gap. Since that time many others have been added, and there are now (1887) 264, known to exist

Only two of these planets, Ceres and Vesta, are sometimes visible to the naked eye ; the largest being only 228 miles in diameter. The force of gravity must be very small. The inhabitants of these planets can all be clowns, for a man could easily jump 50 feet high on one of their surfaces and sustain but a slight shock on descending. There are evidences of an atmosphere on some of the planets.

Some of them also seeem to rotate on their axis.