History of Astronomy From Roman Empire to the Present, part 9
Ideas that have been familiar to us from our very earliest childhood, which we have heard echoed on every hand, and seen reflected in a thousand ways, are tremendously hard to shake. We seem to love them as part of ourselves, and cling to them in the face of the most overwhelming evidence to the contrary.
So it often happens that men and women whose common sense and reason tells them that many of the statements of astronomy are as incredible as the story of Jack and the Beanstalk, are still long to part with their life-long beliefs, and suggest that, after all, the modern theory must be true because astronomers are able to predict eclipses.
But the Chaldeans used to predict the eclipses three thousand years ago; with a degree of accuracy that is only surpassed by seconds in these days because we have wonderful clocks which they had not. Yet they had an entirely different theory of the universe than we have. The fact is that eclipses occur with a certain exact regularity just as Christmas and birthdays do, every so many years, days and minutes, so “that anyone who has the records of the eclipses of thousands of years can predict them as well as the best astronomers, without any knowledge of their cause.
The shadow on the moon at the lunar eclipse is said to be the shadow of the earth, but this theory received a rude shock on February 27th, 1877, for it is recorded in M. Camille Flammarion’s “Popular Astronomy” that an eclipse of the moon was observed at Paris on that date in these circumstances:” the moon rose at 5.29, the sun set at 5.39, and the total eclipse of the moon began before the sun had set.”
The reader will perceive that as the sun and moon were both visible above the horizon at the same time for ten minutes _ before sunset, the shadow on the moon could _____ not be cast by the earth. (See diagram 31.)
Camille Flammarion, however, offers the following explanation: He says, “This is an appearance merely due to refraction. The sun, already below the horizon, is raised by refraction, and remains visible to us. It is the same with the moon, which has not yet really risen when it seems to have already done so.” “
Here is a case where modern astronomy expects us to discredit the evidence of our own senses, but to believe instead their impossible theories. . . This Atmospheric Refraction is supposed to work both ways, and defy all laws. It is supposed to throw up an image of the sun in the west— where the atmosphere is warm, and at the same time to throw up an image of the moon in the east— where it is cool! It is absurd.
When speaking of the measurement of the distance to Mars by Sir David Gill, in the same year, 1877, Sir Norman Lockyer described it as “One of the noblest achievements in Astronomy, upon which depends the distance to and the dimensions of everything in the firmament except the moon.” Evidently a very big thing, worthy of our best attention. The method which Sir David Gill used was the “Diurnal Method of Measurement by Parallax,” which we have dealt with in an earlier chapter. He adopted the suggestion made by Dr. Hailey, and took the two observations to Mars himself, at Ascension Island, in the Gulf of Guinea.
The prime object of the expedition was really to find the distance to the sun (though we remember “that that had been done by Encke fifty years before by the Transit of Venus), which was to be done by first measuring the distance to Mars, and, having found that, by multiplying the result by 2.6571 (roughly 3), as suggested by Kepler’s Theory of the relative distances of the sun, earth and planets, in this manner: Distance to Mars, 35,000,000X2.6571 = 93,000,000 miles.
The Encyclopaedia Britannica tells us that “The sun’s distance is the indispensable link which connects terrestrial measures with all celestial ones, those of the moon alone excepted, hence the exceptional pains taken to determine it,” and assures us later that “The first really adequate determinations of solar parallax were those of Sir David Gill— result 8.80”,’’ and that his measures “have never been superseded.”
He found the Angle of parallax of Mars to be about 23*, which made its distance to be 35 million miles, and this, multiplied by 2.6571, showed the sun to be 93 million miles in the opposite direction. We realize that although the sun’s distance is said to be the indispensable link, it depends upon the measurement to Mars, so that this is more indispensable still. It is the key to all the marvellous figures of astronomy, and for that reason we will give it special treatment.
The figure 35,000,000 miles depends upon the angle at the planet, which is an angle of parallax. That is—the apparent change in the direction of Mars to the right or left of the star x (star of reference) when both are viewed from the opposite ends of a base-line, which, in this case, is the diameter of the earth; see diagram 15. Theory; If Mars is much nearer than x, and both are on a line perpendicular to the centre of the earth, an observer at A will see the planet to the left or east of the star, while B will see it to the right or west of that star. (East and west are local terms, and change with the position of the observer.)
The star of reference is presumed to be billions of miles away, so far away, indeed, that it is supposed to have no angle at all, so that the lines A x and B x are really parallel to each other, and at right angles to the baseline, as shown in diagram 16. Even Mars is at a tremendous distance, so that the angle of parallax is the very small fraction of a degree by which the planet is less perpendicular than the star.
Nevertheless, however slight the apparent nj displacement of Mars may be, if it is between the two perpendiculars A X , and B x, the lines of sight A M and B M would meet L some where at a point.
So far we have supposed A and B to be making observations Motions at the same time, but Sir David Gill believed with Dr. Hailey that he might take the two observations himself, the first from A in the evening, and the second from B the next morning, allowing the rotation of the earth to carry him round from A to B during the night, and that these two observations would give the same result as two observations take by A and B at the same Greenwich time.
Accordingly he took two observations at Ascension Island, one to his east and the other to the west, and, replying upon all the theories of his predecessors, failed to perceive that his second line of sight to the planet was on the wrong side of the perpendicular, and diverged from the first.