The young astronomer ...

Front matter

THE

OB

4-fc

Introduction to the National Reader

National Reader.

The Juvenile Lyre, or Hymns and Songs, set to appropriate Music for Common Schools, by L. Mason.

The First Book of History, or History on the basis of Geography. Being the History of all the Countries in North and South America, illustrated and rendered attractive and interesting to children by the introduction of Anecdotes, sixty Cuts, and sixteen beautiful Maps from steel plates. By the Author of Peter Parley's Tales.

REMARKS TO TEACHERS.

We do not give to children the abstract, philosophical principles of the several sciences. They are first taught the most interesting and useful facts belonging to each science ; and, as their minds become more perfectly formed, we introduce the more abstruse phenomena and principles. The science of Astronomy seems not, however, to have been so far divested of its more difficult parts, as to be adapted to our ' Common Schools ; and, therefore, our children grow up in ignorance of much valuable truth relating to this subject, which they are capable of receiving.

It may be of use to Teachers, to remark that the author designed this little work for those children, who have once properly studied their larger Geography. It is believed that all such children will be found capable of understanding so much of Astronomy as is treated of in this book ; and it will assist them in understanding many parts of Geography. After studying this work, they may review the two sciences separately, or in connexion with each other, as may be found most convenient.

Although this work is particularly designed for schools, and is therefore a book for study rather than simple reading, yet, those who have

IV REMARKS TO TEACHERS.

not leisure to study it regularly, may derive from it much information.

« And it is recommended that even persons of this class should pay particular attention to the questions at the end of each paragraph. They will thereby be greatly assisted in understanding what are the leading, practical truths, which the author designed to teach.

The mode of questioning here presented is thought to be well adapted, to make the scholar learn his lessons thoroughly, and to be well suited to this science. The teacher will find it useful, to add many other questions and examples ; but each part of a lesson should receive its proper share of attention, and caution should be used, that leading facts and principles be not lost in a display of minor facts and circumstances.

The last two chapters are shorter than was designed, because less room was left for them than was expected. But they are not among the most important parts of the work ; and the obliging Teacher will not find it difficult to supply the few facts which are here omitted.

ASTRONOMY.

INTRODUCTORY CHAPTER.

1. Astronomy treats of the Sun, Moon, Planets, Stars, and other heavenly bodies. Before you can well understand what we have to say about these wonderful things, you must learn the meaning of a few words that we shall often use. You must also have a ball, with a hole through its middle, and a stick in it. An apple or an orange will answer the purpose ; but a wooden ball will be better.

What does Astronomy treat of?

2. Your ball is a globe or sphere. Everything, whether great or small, that is shaped like a ball, is called a globe or sphere. An apple, an orange, this great Earth on which we live, the Moon, the Planets, and the Sun are all shaped in nearly the same manner, and we therefore say that they are globular or spherical.

What is a globe ? Mention several spheres, both large and small.

3. We cannot make a good picture of a ball on paper, but

A

ASTRONOMY.

this will help to explain some things respecting your wooden ball; and all other globes.

4. The axis of a globe is a line passing through its centre, as the hole or stick goes through your ball ; and when the globe turns round, it turns on its axis.

5. Mark N. and S. on the ball as they are marked in the picture, and hold it so that N. will point to the North, and S. to the South ; and call those parts of the ball the North Pole and the South Pole.

What is the end of the axis called, which points to the north ? What is the opposite end called ?

6. The equator is a line surrounding a globe at an equal distance from each pole. Make a mark with a piece of chalk, or pass a string round your ball in this manner, and it will represent its equator. The term equator commonly denotes a line round the globe on which we live, at an equal distance from the North Pole and the South Pole.

What is the equator %

DEFINITIONS. 7

7. The diameter of a globe is any straight line passing through the middle of it, as the stick runs through the ball. So also any straight line passing through the centre of a circle, from one side to the other, is its diameter.

What is the diameter of a globe or a circle ?

8. The circumference of a globe is the distance around it in the middle. Thus the equator measures the circumference ; and a line passing round the middle in any other direction, will do the same.

What is the circumference of a globe ?

9. The circumference of a globe or a circle, is about three times as great as its diameter.

If your ball is two inches in diameter, what is its circumference ? If the diameter were 1 foot, what would be the circumference ? The Earth is about 8 thousand miles in diameter ; what is the distance round it ? If a hoop is 9 feet in circumference, what is its diameter? I once measured round a tree, and found the distance 24 feet 9 inches; what was its diameter ?

10. You can see that the circumference of any globe is a circle. Thus, the equator is a circle, and any line drawn in a similar manner round your ball, is a circle. We divide every circle into 360 degrees. Whether the circle be large or small, it has the same number of degrees. The degrees of large circles are longer than those of small ones. You will see that

a2

ASTRONOMY.

a part of this large circle is divided into single degrees ; and both circles are divided into halves and quarters. A quarter of a circle is 90 degrees : it is sometimes called a quadrant. A half of a circle is 180 degrees : it is often called a semicircle.

DEFINITIONS. V)

How many degrees are there in a circle ? How many degrees make a quadrant ? How many make a semicircle ? Are the degrees of all circles of the same length ?

11. Degrees are sometimes divided into equal parts, called minutes ; and minutes into equal parts, called seconds. Sixty seconds make a minute, and sixty minutes a degree. Degrees are marked with a small cipher ; minutes with a small accent ; and seconds with a double accent. Thus, 10° 12' 11" are ten degrees, twelve minutes, and eleven seconds.

How many seconds make a minute ? How many minutes a degree ? How many degrees a circle ? Read these figures, 20° 14/ 17 /; . Read these, 140° 23' 39".

12. A telescope is an instrument for looking at the sun, moon, planets, and other distant objects. It causes distant objects to appear nearer. There are several kinds of telescopes, hut they are all fitted with such glasses, as make distant objects appear larger and nearer, and thus enable us to see them better.

What is the use of a telescope ?

Chapter I. The Sun, ©

1. The Sim is a great globe : it is much larger than anything else that we know. When we look at it without a telescope, it does not appear to be more than one or two feet in diameter ; but the best telescopes make it appear very much larger. Astronomers have discovered several methods of ascertaining its size ; and they find its diameter to be more than 860 thousand miles. The Sun is more than a million times larger than this earth.

What is the shape of the Sun ? How great is its diameter ? What do you mean by the diameter of a globe ? How much larger is the Sun than the earth ?

2. The Sun appears small, because it is so far from us. You know that all things appear smaller when distant, than when near you. A house can hardly be seen ten miles ; and a little fly that is quite near you, appears larger than an ox that is a mile off. The Sun is about 95 millions of miles from the earth. If a bird could fly towards it, at the rate of two miles every minute, it would require about ninety years to reach the Sun.

Why does the Sun appear so small ? How far are we from the Sun ? How long would it take a pigeon, flying two miles every minute to reach the Sun ?

THE SUN THE PLANETS. 11

3. The Sun gives us light and heat, and you can easily understand that nothing in this world could live without it. It should remind us of the Lord, who is called the Sun of righteousness. His truth is the light o f our minds, and His love gives life to our souls.

What do we receive from the Sun ? Of whom should the Sun remind us?

4. The Sun appears to move round the earth every day, but this is not really the fact.. We shall explain this subject in another chapter. The Sun does, however, turn round on its own axis once in twenty five and a half days.

Does the Sun revolve round the earth ? In what time does it revolve on its own axis ?

Turn your ball round upon the stick that runs through it, and you will see how the Sun turns on its axis.

Chapter II. The Planets

1. There are eleven large globes, which revolve about the sun, and are called Planets. This earth on which we live is one of the Planets ; and w r e should not doubt that the others have inhabitants, who enjoy the manifold blessings of Him who is Lord over all.

ASTRONOMY.

How many Planets are there? What is their shape? Do the Planets revolve round the sun, or does the sun revolve round the Planets ?

2. The names of the Planets are Mercury, Venus, the Earth, Mars, Vesta, Juno, Pallas, Ceres, Jupiter, Saturn, and Uranus or Herschel. Mercury is the nearest to the sun, and

THE PLANETS.

you will see the comparative distances of all, except Saturn and Uranus, in this figure. These two are so much further than Jupiter, that there is not room here to represent their distances. Pallas and Ceres are so nearly at an equal distance, that one circle is marked for both.

What are the names of the Planets ? How many are nearer the sun than the earth is ?

Circle.

3. The line or path in which a Planet goes round the sun, is called its orbit.

When a Planet is going round the sun, it does not keep at the same distance all the time ; but is sometimes nearer the sun than at others. Hence its orbit is not a circle ; it is an ellipse.

You will see the difference between a circle and an oval or ellipse by these figures.

What is the orbit of a Planet ? What is the shape of the orbits of the Planets ? Is a Planet always equally distant from the sun ?

4. The time in which a Planet goes round the sun, is called a year. You know that a year on this earth is 365^ days. It is 365 days when it is not leap-year, and 366 clays when it is leap-year; and, leap-year comes once in four years. Some of the Planets have much longer years, but Mercury and Venus have shorter.

What is a year ? How long is a year on this earth ? How many days is the year in leap-year? Have any of the Planets longer years? Have any of them shorter years ?

5. The time in which a Planet revolves once on its own axis, is a day. We begin our day at midnight, and divide it into 24 hours. Most of the Planets revolve in much less time than the earth does, and therefore have shorter days.

What is a day ? At what time do we begin our day? Into how many hours is it divided ? Are the days on the other Planets just as long as ours ?

6. We said that the Planets are not all of the same size. This picture will show the comparative size of most of them : the others are too small to be well compared in a picture. The marks, placed before the names of the Planets, are those which are often used instead of the names in Almanacs and books of Astronomy.

Which Planet is the largest ? Which has a great ring round it? How many of the Planets are larger than the Earth ?

THE PLANETS MERCURY.

7. Several of the Planets are frequently seen by us in clear evenings. They give a more steady, or less twinkling light, than the stars ; but most persons do not observe the difference.

Are any of the Planets ever seen by us ? How do they appear ?

Chapter III. Mercury, $

1. We shall now give a more particular account of each of the planets. Mercury is much nearer to the sun than either of the others. Its mean distance is about 37 millions of miles. It is sometimes a little more, and sometimes a little less distant; but this is its mean or average distance.

Note. To find the mean or average of two numbers, add them together and divide their sum by 2. To find the mean of three numbers, add them, and divide by 3. To find the mean of fifty numbers, add, and divide by 50. The same rule applies to all cases. Thus, find the mean of 4, 5, 6, 9. These make 24; and there are four distinct numbers. Divide 24 by 4, and the answer is 6.

Which planet is nearest the sun ? How far is it ? Is it always just 37 millions? What is the mean or average of 9, 8, 4, 11? If you walk a part of a day at 2 miles an hour, an equal part at 3 miles an hour, and an equal part at 4 miles an hour, how many miles an hour does it average ? If one boy can throw a stone 10 rods, and another boy can throw it 20 rods, what is the mean distance ?

2. Mercury revolves on its axis from west to east once in 24 hours, and revolves round the sun in about 88 days.

How long is a day at Mercury ? How long is a year ? How many of our months are there in a year of Mercury ? How many seasons have we ? If Mercury has four seasons, how long is each ?

3. Mercury never appears far from the sun. It is commonly so near, that the brightness of the sun prevents our seeing it ; but it is sometimes visible a little after sunset. The apparent distance of a planet from the sun is called its elongation. Try now to understand this. Point your finger towards the east. Now move it over slowly till it points to the west. It has moved just half 9. circle, and that is 18.0

MERCURY. 17

degrees. Move it now from the horizon to the zenith or the point directly overhead. That is a quarter of a circle or 90 degrees. Half of the distance from the horizon to the zenith is 45 degrees. You will see this plainly by the figure on p. 8. Mercury never appears more than 28 degrees from the sun ; that is, its greatest elongation is 28°.

Is Mercury often seen ? Why is it seldom visible ? What is the elongation of a planet ? How many degrees is it from east to west, or from any part of the horizon to the opposite part ? How far from the horizon to the zenith ? What is half that distance ? What is the greatest elongation of Mercury ?

4. The sun appears to move round the earth once in 24 hours. The whole distance that it appears to go, is a circle.

How many degrees make a circle ? How many degrees does the sun appear to move in 24 hours ? How many in one hour ? How many in two hours ? How many hours does it take for the sun to appear to move 90 degrees ? When the days from sunrise to sunset are twelve hours long, how many degrees does the sun appear to move in the day?

Remember that the apparent motion of the sun and stars j is 15 degrees an hour.

5. Mercury is a small planet ; it is about one fifteenth part as large as this earth. Its diameter is about '3000 miles.

Is Mercury as large as this earth ? What is its diameter ? Recollect how much more the circumference of a globe or circle is, than its diameter ; and then find the circumference of Mercury.

6. Mercury is so much nearer the sun than this earth is, that the climate is probably warmer : but Ave do not know that it is warmer and lighter in proportion as it is nearer the sun.

Is there probably more heat and light at Mercury, than we have ?

CHAPTER IT.

VENUS, ?.

1. Venus is the most beautiful of all the planets that we can see. Its light is very white and pleasant. We see it very frequently for several hours in the evening, or early in the morning. Its greatest elongation, or apparent distance from the sun, is 47°.

What is the appearance of Venus? Can we often see it? How many hours high does Venus ever appear after the sun sets ? How many hours does it sometimes rise before the sun ? The number of hours thai it sets after the sun, or ?ises before the sun, is found by seeing how many times 15 degrees there are in 47°.

2. Venus is almost as large as the earth. Its mean distance from the sun is 68 millions of miles : it revolves on its axis from west to east in a little less than 24 hours ; and revolves round the sun in 7-J of our months.

How large is Venus ? What is its mean distance from the sun ? How long is a day at Venus ? How long is a year ?

VENUS.

3. When Venus is seen through a telescope it appears very differently from what it does to the naked eye. We do not see the whole of that half of it on which the sun shines, and therefore it does not appear round. You know how differently the moon appears at different times ; and Venus and Mercury have similar appearances when we look at them with a telescope. This picture will help you to understand what is here said.

How does Venus appear when we look at it through a telescope ?

4. You must remember that, neither the planets nor the moon give any light that is their own. The sun shines on them, and they reflect some of the light to us. But the sun shines only on one side of a planet or moon at one time ; and the other side is dark. Sometimes we see but a small part of the side on which the sun shines, and then it does not appear round, nor give much light.

Does Venus shine with her own light ? What gives it light ? Does the sun shine all around a planet or moon ?

5. How delightful it is, to learn our own duty while we are studying these works of the Lord. The sun is the lord of this lower world. It gives light to all those globes tKat revolve about it ; and they send around to each other a part of what the sun gives them. So the Maker and Ruler of all worlds, imparts to us and to all his children the light of our minds, which is Truth ; and He requires that each one should impart to others from the light which he receives.

Who gives light to all men ? What is that light ? What does He require of each one ?

6. Mercury and Venus are sometimes called interior or inferior planets, because their orbits are within the earth's orbit, or nearer to the sun. The orbits of the other planets are without the earth's orbit, or farther from the sun, and they are called exterior or superior planets.

Why are Mercury and Venus called interior planets ? What are those called, that are farther from the sun than the earth is ?

THE EARTH. 21

Chapter V. The Earth, 0

1. The Earth on which we live does not appear like a globe when we look upon it ; but it is so large, that we can see only a very small part of it If the smallest fly or bug were placed on an orange or an apple, it could see but a little distance, and the parts around it would appear rough with hills and valleys, as the earth does to us. But we know that the Earth is a globe or sphere, because many men have sailed round it, which they could not do if it had a different shape. There are also other proofs that the Earth is a globe, which we shall attend to hereafter.

What is the shape of the Earth ? How is this known ?

2. The diameter of the Earth is about 8,000 miles. It turns round on its axis from west to east in about 24 hours, which make one day ; and revolves round the sun once in a year, or 365^.

How many miles is the diameter of the Earth ? How many is the circumference ? Which way does it revolve on its axis ? How long is one revolution on its axis ? How long is a revolution round the sun ?

3. Be careful to remember, that this Earth is a globe, or ball ; that it is a planet ; that it turns round from w-2st to east on its axis, and that the time in which it turns once round is

B

ASTRONOMY.

called a day : that it also goes round the sun, and that the time in which it goes once round the sun is called a year. What things must you carefully remember?

4. If you hold your ball towards the sun or a candle, the light will shine on one half of it at a time. Turn it round from west to east, and each part will come to the light, and then go away from it every time that the ball turns round. In this way the sun shines on the Earth while the Earth turns round. If a fly were on the ball, the sun or candle would appear to the fly to move from east to west : so "while the Earth turns from west to east, the sun appears to move from east to west. This is like what you notice when sailing rapidly in a boat or ship, or riding in a coach : the trees and houses, and fences which you pass, appear to move in the opposite direction.

On how great a part of the Earth does the sun shine at once ? Why does the sun appear to move from east to west ?

5. Everything that is on this globe turns round with it ; and the air and clouds that are around us, also revolve with the Earth. It is because these things all move round quietly with us, that we do not notice their motion. So, when you sit in the cabin of a large boat or ship, and sail smoothly along, you cannot see that anything in the cabin moves. If you look out upon the land, the things which you there see,

THE EARTH. 23

appear to move backwards ; so. when you loo'c away from the Earth; and see the sun, mo^n. or stars, they appear to move backwards towards the west, because they do not go with the Earth.

Do yon, and the trees, houses, and all things on the Earth, revolve with it once in a day ? Why do not these things appear to move ? Why do the sun, moon, and stars, appear to move from east to west?

6. We revolve with the Earth once in a day. If we lived at the equator, we should go as far in a. day. as the whole circumference of the Earth : but we live nearly hallway between the equator and the north pole. Now. measure round your ball at the equator : then measure round it about half way from the equator to the pole. You find the distance much less here, than at the equator. Make a little dot at the equator, and another where you last measured round the ball. Now. revolve it slowly ; and you can see that the last dot does not go so far in revolving once, as the other does. It revolves in the same time, but goes slower. Those people, therefore, who live at the equator, revolve 24,000 miles in a day : but others revolve slower, and a less distance in a day, in proportion to their distance from the equator.

Do you move as fast with the Earth, as the people at the equator ? How far do they move in a day ? Why do you not go as far ?

7. As the people at the equator are carried about 24,000 miles in a day, they must be carried a twenty fourth part of b2 that distance in an hour, and that is 1000 miles. The people of Philadelphia, and other places in latitude 40°, are carried 800 miles in an hour. The people of Boston, and others in latitude about 42J° are carried 770 miles in an hour. The people of St. Petersburgh, and others in latitude 60°, are carried about 500 miles in an hour.

How far are people at the equator carried in a day by the Earth's revolution on its axi3 ? How far in an hour ? How far are those carried who live in latitude 40° ? Those in latitude 42J° 1 Those in 60° ?

8. You will now understand about the Earth's motion on its axis ; and we will proceed for a while to talk of other things.

Chapter VI. The Moon, D

1. The eleven planets that we have mentioned, are called 'primary planets. Some of them have a small kind of planets that revolve about them, and go with them round the sun. These are called Moons, secondary planets, or satellites. Mercury and Venus have no Moons ; our Earth has one ; some of the planets have several Moons.

Have Mercury and Venus any Moons ? How many has the Earth ? Has any planet more ?

THE MOON.

2. The beautiful Moon, which shines on the earth so sweetly in the night, is 240 thousand miles from us. It revolves round the earth, as a little ball round a large one, in 29 J days ; and it revolves on its axis in the same time.

How far is the Moon from the earth ? In what time does the Moon go round the earth ? How long is a day at the Moon?

3. The diameter of the Moon is about 2000 miles. To the people of the Moon the earth appears as the Moon does to us, except that it probably appears much larger.

How large* is the Mcon ? How does the earth appear to the lunarians, or inhabitants of the Moon ?

4. When we look at the Moon through a telescope, it has a very rugged appearance. Those parts which are brightest are supposed to be high lands and mountains ; .and the darker parts to be valleys. The cut on the next page will give you some idea of the appearance of the Moon when seen through a telescope.

What are the brightest parts of the Moon supposed to be ? What are the darker parts ?

5. There is but little air about the Moon, and probably little water upon it. *We could not live there ; but it is doubtless a very good world for such people as live there- Is the Moon supplied with air and water so well that we could live

on it ?

ASTRONOMY.

6. You must remember that the Moon does not shine with its own light ; it receives light from the sun, and reflects it to us. The earth also receives light from the sun, and reflects it to the Moon and the other planets,

MARS. 27

Does the Moon shine with its own light ? Whence does it receive light ? We shall explain several other important things concerning the Moon in another part of this book.