be a stargazer - header

PREFACE

All sciences are making an advance, but Astronomy is moving at high speed. Since the principles of this science were settled by Copernicus, four hundred years ago, it has never had to beat a retreat. It is rewritten not to correct material errors, but to incorporate new discoveries.

At one time, Astronomy studied mostly tides, seasons, and telescopic aspects of the planets; now these are only primary matters. Once it considered stars as mere fixed points of light; now it studies them as suns, determines their age, size, color, movements, chemical constitution, and the revolution of their planets. Once it considered space as empty; now it knows that every cubic inch of it quivers with greater intensity of force than that which is visible in Niagara. Every inch of surface that can be conceived of between suns is more wave-tossed than the ocean in a storm.

The invention of the telescope constituted one era in Astronomy; its perfection in our day, another; and the discoveries of the spectroscope a third—no less important than either of the others. New discoveries are made every day with the advancement of telescopes. The Hubble space telescope has let man see further into the universe then ever before. Astronomy and space science is an ever-changing study, and possibly the most exciting of the sciences. It is for one reason that this book was written, to hopefully interest more people in the exciting study of the universe around us.

TABLE OF CONTENTS

Why Study Light? ……………………………………………………………………………………….. 4
Introduction to Light ……………………………………………………………………………………. 5
ASTRONOMICAL INSTRUMENTS …………………………………………………………… 14
Our Solar System ………………………………………………………………………………………… 18
The Sun ………………………………………………………………………………………………………… 20
Earth’s Moon ……………………………………………………………………………………………….. 22
The Planets ………………………………………………………………………………………………….. 27
Asteroids ………………………………………………………………………………………………………. 65
Meteoroids ……………………………………………………………………………………………………. 67
Comets ………………………………………………………………………………………………………….. 69
Kuiper Belt …………………………………………………………………………………………………….. 71
Beyond Our Solar System …………………………………………………………………………… 73
The Stars ……………………………………………………………………………………………………….. 75
The Constellations ……………………………………………………………………………………….. 94
FINDING THE STARS IN THE SKY ……………………………………………………………. 101

Why Study Light?

For most of history, humans have used visible light to explore the skies. With basic tools and the human eye, we developed sophisticated
methods of timekeeping and calendars. Telescopes were invented in the 17th century. Astronomers then mapped the sky in greater detail––still with visible light. They learned about the temperature, constituents, distribution, and the motions of stars.

There are two main techniques for analyzing starlight. One is called spectroscopy and the other photometry. Spectroscopy spreads out the
different wavelengths of light into a spectrum for study. Photometry measures the quantity of light in specific wavelengths or by combining all wavelengths. Astronomers use many filters in their work. Filters help astronomers analyze particular components of the spectrum. For example, a red filter blocks out all visible light wavelengths except those that fall around 600 nanometers (it lets through red light).

Introduction to Light

Light is a form of radiant energy or energy that travels in waves. Since Greek times, scientists have debated the nature of light. Physicists now recognize that light sometimes behaves like waves and, at other times, like particles. When moving from place to place, light acts like a system of waves. In empty space, light has a fixed speed and the wavelength can be measured. In the past 300 years, scientists have improved the way they measure the speed of light, and they have determined that it travels at nearly 299,792 kilometers, or 186,281 miles, per second.

When we talk about light, we usually mean any radiation that we can see. These wavelengths range from about 16/1,000,000 of an inch to 32/1,000,000 of an inch. There are other kinds of radiation such as ultraviolet light and infrared light, but their wavelengths are shorter or longer than the visible light wavelengths. When light hits some form of matter, it behaves in different ways. When it strikes an opaque object, it makes a shadow, but light does bend around obstacles. The bending of light around edges or around small slits is called diffraction and makes patterns of bands or fringes.

All light can be traced to certain energy sources, like the Sun, an electric bulb, or a match, but most of what hits the eye is reflected light. When light strikes some materials, it is bounced off or reflected. If the material is not opaque, the light goes through it at a slower speed, and it is bent or refracted. Some light is absorbed into the material and changed into other forms of energy, usually heat energy. The light waves make the electrons in the materials vibrate and this kinetic energy or movement energy makes heat. Friction of the moving electrons makes heat.

Experiments With Light

A light set in a room is seen from every place; hence light streams in every possible direction. If put in the centre of a hollow sphere, every point of the surface will be equally illumined. If put in a sphere of twice the diameter, the same light will fall on all the larger surface. The surfaces of spheres are as the squares of their diameters; hence, in the larger sphere the surface is illumined only one-quarter as much as the smaller. The same is true of large and small rooms. In Fig. 7 it is apparent that the light that falls on the first square is spread, at twice the distance, over the second square, which is four times as large, and at three times the distance over nine times the surface. The varying amount of light received by each planet is also shown in fractions above each world, the amount received by the earth being 1.

Click to Read Full eBook

 

Comments

FREE ONLINE READING

Login! You can free to read most online eBooks instantly!

FREE DOWNLOAD

Login! You can free to download many eBooks quickly!

FREE DELIVERY & RETURN

Free deliver eBook and return your order anywhere in the world!