Читать книгу Star-land: Being Talks With Young People About the Wonders of the Heavens - Robert S. Ball - Страница 6

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The sun is a very long way off. It is not easy for you to imagine a distance so great, but if you want to learn astronomy you must make the attempt. This is the first measurement that we shall have to make on our way to that far-off country called Star-Land; but long as we shall find it to be, we shall afterwards have to consider distances very much longer. When you are out in the street, or taking a walk in the country, you can see at once that this man is near, or that house is far, or that mountain is many miles away. This is because you have other objects between to help you to judge of the distances of these different objects. You will see, for example, that there are many houses or farmyards, and you will notice hedges dividing different fields between you and the mountain. You also see that there are woods and parks, and perhaps stretches of moorland extending up the slopes. You have an impression that the farmyards and fields are of considerable size, and that the woods or moors are wide and extensive; and putting these things together, you realize that the mountain must be miles away.

But when we look at the sun we have no aids conveniently placed to help us in judging his distance. There are no intervening objects, and merely gazing at the sun helps us but little in obtaining any accurate knowledge. We must go to the astronomer and ask him to tell us how far he has found the sun to be, and then we must also beg from him some explanation of the method he has used in making his measurements.

It has been found that the sun is, on the average, about ninety-three millions of miles from the earth; but sometimes it is a little further and sometimes it is a little nearer. Let us first try to count 93,000,000. The easiest way will be to get the clock to do this for us; and here is a sum that I would suggest for you to work out. How long will the clock have to tick before it has made as many ticks as there are miles between the earth and the sun? Every minute the clock, of course, makes 60 ticks, and in 24 hours the total number will reach 86,400. By dividing this into 93,000,000 you will find that more than 1076 days, or nearly three years, will be required for the clock to perform the task.

We may consider the subject in another way, and find how long an express train would take to go all the way from the earth to the sun. We shall suppose the speed of the train to be 40 miles an hour; and if the train ran for a whole day and a whole night without stopping, it would then accomplish 960 miles. In a year the distance travelled would reach 350,400 miles, and by dividing this into 93,000,000 we arrive at the conclusion that a train would have to travel at a pace of 40 miles an hour, not alone for days and for weeks and for years, but even for centuries. Indeed, not until 265 years had elapsed would the mighty journey have been ended. Even though King Charles I. had been present when the train began to move, the destination would not yet have been reached. No one who started in the train could expect to reach the end of the trip. That would not occur till the time of his great-great-grandchildren.