History of Astronomy From the Roman Empire to the Present, Part 7
A GALAXY OF BLUNDERS
The world of astronomy being satisfied that Encke had really found the distance of the sun, the time
had come when a triangulation to the stars might be attempted; and this was done by F. W. Bessel in the year 1838. He is said to have been the first man to make a successful measurement of stellar distance when he estimated the star known as “61 Cygni ” to be 10 ½ light-years, or 63,000,000,000,000 miles from the earth; its angle of parallax being 0.31”; and for this work Bessel is regarded as virtually the creator of Modern Astronomy of Precision.
The reader who has followed me thus far will suppose that I intend to examine this measurement of “61 Cygni.” That is so, but as it will be necessary to introduce astronomical terms and theories which will be unfamiliar to the layman, I must explain these at some length in order that he, as one of the jury, may be able to arrive at a just verdict. In the meantime I respectfully call the attention of the responsible authorities of astronomy to this chapter, for it is probable that I shall here shatter some of their most cherished theories, and complete the overthrow of the Copernican astronomy they represent.
Light is said to travel at a speed of 186,414 miles a second; that is 671,090,400 miles in an hour, or six billion (six million millions) miles in a year. So when “61 Cygni” is said to be 10 ½ light-years distant it means that it is so far away that it takes its light ten and a half years to travel from the star to the eye of the observer, though it is coming at the rate of 671,090,400 miles an hour. One light-year equals 6,000,000,000,000 miles.
An “angle of parallax” is the angle at the star, or at the apex of an astronomer’s triangulation. The angle of parallax 0.31″ (thirty-one hundredths of a second of arc) is so extremely small that it represents only one 11,613th part of a degree. There is in Greenwich Observatory an instrument which has a vernier six feet in diameter, one of the largest in the world. A degree on this vernier measures about three quarters of an inch, so that if we tried to measure the parallax 0.31” on that vernier we should find it to be one 15,484th part of an inch. When angles are as line as this we are inclined to agree with Tycho Brahe when he said that “Angles of Parallax exist only in the minds of the observers ; they are due to instrumental and personal errors.”
The Bi-annual (or semi-annual) method of stellar measurement which Bessel used for his triangulation is very interesting, and, curiously enough, it is another of those singularly plausible inventions advocated by Dr. Hailey.
It will be remembered how Hipparchus failed to get an angle to the stars 2,000 years ago, and arrived at the conclusion that they must be infinitely distant ; and we have seen how that hypothesis has been handed down to us through all the centuries without question, so we can understand how Dr. Hailey was led to design his method of finding stellar distance on a corresponding, infinitely
It appeared to him that no base-line on earth (not even its diameter) would be of any use for such an immense triangulation as the stars required, but he thought it might be possible to obtain a base-line long enough if we knew the distance of the sun; and his reasoning ran as follows; As we have learned from Copernicus that the earth travels completely round the sun once in a year, it must be on opposite sides of the orbit every six months, therefore, if we make an observation to a star — let us say—tonight, and another observation to the same star when we are on the other side of the orbit in six months’ time, we can use the entire diameter of the orbit as a base-line.
Of course this suggestion could not be put mto practice until the distance to the sun was found, but
now that Encke had done that, and found it to be about 97,000,000 miles, Bessel had only to multiply that by two to find the diameter of the orbit, so that the length of his base-line would be, roughly, 194,000,000 miles.
It seemed a simple matter, then, to make two observations to find the angle at the star “61 Cygni,” and to multiply it into the length of the base-line just as a surveyor might do.
A critical reader might observe that as there is in reality only one earth, and not two, as it appears in diagram 11, the base-line is a very intangible thing to refer any angles to; and he might think it impossible to know what angles the lines of sight really do subtend to this imaginary base-line ; but these questions do not seriously concern the astronomer because the “Theory of Perpendicularity” assures him that the star is at all times perpendicular to the centre of the earth, while the “Theory of Parallax” enables him to ignore the direction of his base-line altogether, and to find his angle— not at the base ! but at the apex of the triangle— at the star.
These theories, however, deserve our attention; Parallax is “the apparent change in the direction of a body when viewed from two different points.” For example, an observer at A in diagram 12, would see the tree to the left of the house, but if he crosses over to B, the tree will appear to have moved to the right of the house. Now in modern astronomy the stars are supposed to be fixed, just as we know the tree and the house to be, and an astronomer’s angle of parallax is “the apparent change in the direction of a star as compared with another star, when both are viewed from two different points, such as the opposite sides of the orbit.
“The Theory of Parallax” as stated in astronomy, is “that the nearer the star the greater the parallax; hence the greater the apparent displacement the nearer the body or star must be.” In other words, it is supposed that because the tree in the diagram is nearer to the observer than the house, it will appear to move further from the house than the house will appear to move away from the tree, if the observer views them alternately from A and B. That is the principle which Bessel relied upon to find the parallax of “61 Cygni.” (I will leave the reader to make his own comments upon it.)