Gore John Ellard
Astronomical Curiosities: Facts and Fallacies
Messier, who was called “the comet ferret,” discovered “all his comets with a small 2-foot telescope of 2¼ inches aperture, magnifying 5 times, and with a field of 4°.”224
It is a very curious fact that Sir William Herschel, “during all his star-gaugings and sweeps for nebulæ, never discovered a comet;”225 that is an object which was afterwards proved to be a comet. Possibly, however, some of his nebulæ which are now missing, may have been really comets.
Sir William Herschel found the diameter of the head of the great comet of 1811 to be 127,000 miles. The surrounding envelope he estimated to be at least 643,000 miles, or about three-fourths of the sun’s diameter.
On a drawing of the tails of the great comet of 1744 given in a little book printed in Berlin in that year, no less than 12 tails are shown! These vary in length and brightness. A copy of this drawing is given in Copernicus.226 The observations were made by “einen geschichten Frauenzimmer,” who Dr. Dreyer identifies with Christian Kirch, or one of her two sisters, daughters of the famous Gottfried and Maria Margaretta Kirch (Idem, p. 107). Dr. Dreyer thinks that the drawing “seems to have been carefully made, and not to be a mere rough sketch as I had at first supposed” (Idem, p. 185).
The tails of some comets were of immense length. That of the comet of 1769 had an absolute length of 38 millions of miles. That of 1680, 96 million of miles, or more than the sun’s distance from the earth. According to Sir William Herschel, the tail of the great comet of 1811 was over 100 millions of miles in length. That of the great comet of 1843 – one of the finest in history – is supposed to have reached a length of 150 millions of miles!227
In width the tails of comets were in some cases enormous. According to Sir William Herschel, the tail of the comet of 1811 had a diameter of 15 millions of miles! Its volume was, therefore, far greater than that of the sun![228]
According to Hevelius the comet of 1652 was of such a magnitude that it “resembled the moon when half full; only it shone with a pale and dismal light.”228
Halley’s comet at its next appearance will be examined with the spectroscope for the first time in its history. At its last return in 1835, the spectroscope had not been invented.
For the great comet of 1811, Arago computed a period of 3065 years; and Encke found a period of 8800 years for the great comet of 1680.229
The variation in the orbital velocity of some comets is enormous. The velocity of the comet of 1680 when passing round the sun (perihelion) was about 212 miles a second! Whereas at its greatest distance from the sun (aphelion) the velocity is reduced to about 10 feet a second!
CHAPTER XII
Meteors
Mr. Denning thinks that the meteor shower of the month of May, known as the Aquarids, is probably connected with Halley’s comet. The meteors should be looked for after 1 a.m. during the first week in May, and may possibly show an enhanced display in May, 1910, when Halley’s comet will be near the sun and earth.230
On November 29, 1905, Sir David Gill observed a fireball with an apparent diameter equal to that of the moon, which remained visible for 5 minutes and disappeared in a hazy sky. Observed from another place, Mr. Fuller found that the meteor was visible 2 hours later! Sir David Gill stated that he does not know of any similar phenomenon.231
Mr. Denning finds that swiftly moving meteors become visible at a greater height above the earth’s surface than the slower ones. Thus, for the Leonids and Perseids, which are both swift, it has been found that the Leonids appear at an average height of 84 miles, and disappear at a height of 56 miles; and the Perseids at 80 and 54 miles respectively. “On the other hand, the mean height of the very slow meteors average about 65 miles at the beginning and 38 miles at the end of their appearance.”232
During the night of July 21-22, 1896, Mr. William Brooks, the well-known astronomer, and director of the Smith Observatory at Geneva (New York), saw a round dark body pass slowly across the moon’s bright disc, the moon being nearly full at the time. The apparent diameter of the object was about one minute of arc, and the duration of the transit 3 or 4 seconds, the direction of motion being from east to west. On August 22 of the same year, Mr. Gathman (an American observer) saw a meteor crossing the sun’s disc, the transit lasting about 8 seconds.233
A meteor which appeared in Italy on July 7, 1892, was shown by Prof. von Niessl to have had an ascending path towards the latter end of its course! The length of its path was computed to be 683 miles. When first seen, its height above the earth was about 42 miles, and when it disappeared its height had increased to about 98 miles, showing that its motion was directed upwards!234
In the case of the fall of meteoric stones, which occasionally occur, it has sometimes been noticed that the sound caused by the explosion of the meteorite, or its passage through the air, is heard before the meteorite is seen to fall. This has been explained by the fact that owing to the resistance of the air to a body moving at first with a high velocity its speed is so reduced that it strikes the earth with a velocity less than that of sound. Hence the sound reaches the earth before the body strikes the ground.235
The largest meteoric stone preserved in a museum is that known as the Anighita, which weighs 36½ tons, and was found at Cape York in Greenland. It was brought to the American Museum of Natural History by Commander R. E. Peary, the Arctic explorer.
The second largest known is that of Bacubirito in Mexico, the weight of which is estimated at 27½ tons.
The third largest is that known as the Williamette, which was found in 1902 near the town of that name in Western Oregon (U.S.A.). It is composed of metallic nickel-iron, and weighs about 13½ tons. It is now in the American Museum of Natural History.
A large meteorite was actually seen, from the deck of the steamer African Prince, to fall into the Atlantic Ocean, on October 7, 1906! The captain of the vessel, Captain Anderson, describes it as having a train of light resembling “an immense broad electric-coloured band, gradually turning to orange, and then to the colour of molten metal. When the meteor came into the denser atmosphere close to the earth, it appeared, as nearly as is possible to describe it, like a molten mass of metal being poured out. It entered the water with a hissing noise close to the ship.”236 This was a very curious and perhaps unique phenomenon, and it would seem that the vessel had a narrow escape from destruction.
In Central Arizona (U.S.A.) there is a hill called Coon Butte, or Coon Mountain. This so-called “mountain” rises to a height of only 130 to 160 feet above the surrounding plain, and has on its top a crater of 530 to 560 feet deep; the bottom of the crater – which is dry – being thus 400 feet below the level of the surrounding country. This so-called “crater” is almost circular and nearly three-quarters of a mile in diameter. It has been suggested that this “crater” was formed by the fall of an enormous iron meteorite, or small asteroid. The “crater” has been carefully examined by a geologist and a physicist. From the evidence and facts found, the geologist (Mr. Barringer) states that “they do not leave, in my mind, a scintilla of doubt that this mountain and its crater were produced by the impact of a huge meteorite or small asteroid.” The physicist (Mr. Tilghmann) says that he “is justified, under due reserve as to subsequently developed facts, in announcing that the formation at this locality is due to the impact of a meteor of enormous and unprecedented size.” There are numerous masses of meteoric iron in the vicinity of the “crater.” The so-called Canyon Diabolo meteorite was found in a canyon of that name about 2½ miles from the Coon Mountain. The investigators estimate that the great meteoric fall took place “not more than 5000 years ago, perhaps much less.” Cedar trees about 700 years old are now growing on the rim of the mountain. From the results of artillery experiments, Mr. Gilbert finds that “a spherical projectile striking solid limestone with a velocity of 1800 feet a second will penetrate to a depth of something less than two diameters,” and from this Mr. L. Fletcher concludes “that a meteorite of large size would not be prevented by the earth’s atmosphere from having a penetration effect sufficient for the production of such a crater.”237
The meteoric origin of this remarkable “crater” is strongly favoured by Mr. G. P. Merrill, Head Curator of Geology, U.S. National Museum.
The Canyon Diabolo meteorite above referred to was found to contain diamonds! some black, others transparent. So some have said that “the diamond is a gift from Heaven,” conveyed to earth in meteoric showers.238 But diamond-bearing meteorites would seem to be rather a freak of nature. It does not follow that all diamonds had their origin in meteoric stones. The mineral known as periodot is frequently found in meteoric stones, but it is also a constituent of terrestrial rocks.
In the year 1882 it was stated by Dr. Halm and Dr. Weinhand that they had found fossil sponges, corals, and crinoids in meteoric stones! Dr. Weinhand thought he had actually determined three genera!239 But this startling result was flatly contradicted by Carl Vogt, who stated that the supposed fossils are merely crystalline conformations.240
Some meteorites contain a large quantity of occluded gases, hydrogen, helium, and carbon oxides. It is stated that Dr. Odling once “lighted up the theatre of the Royal Institution with gas brought down from interstellar space by meteorites”!241
On February 10, 1896, a large meteorite burst over Madrid with a loud report. The concussion was so great that many windows in the city were broken, and some partitions in houses were shaken down!242
A very brilliant meteor or fireball was seen in daylight on June 9, 1900, at 2h 55m p.m. from various places in Surrey, Sussex, and near London. Calculations showed that “the meteor began 59 miles in height over a point 10 miles east of Valognes, near Cherbourg, France. Meteor ended 23 miles in height, over Calais, France. Length of path 175 miles. Radiant point, 280°, 12°.”243
It was decided some years ago “in the American Supreme Court that a meteorite, though a stone fallen from heaven, belongs to the owner of the freehold interest in the land on which it falls, and not to the tenant.”244
With reference to the fall of meteoric matter on the earth, Mr. Proctor says, “It is calculated by Dr. Kleiber of St. Petersburgh that 4250 lbs. of meteoric dust fall on the earth every hour – that is, 59 tons a day, and more than 11,435 tons a year. I believe this to be considerably short of the truth. It sounds like a large annual growth, and the downfall of such an enormous mass of meteoric matter seems suggestive of some degree of danger. But in reality, Dr. Kleiber’s estimate gives only about 25 millions of pounds annually, which is less than 2 ounces annually to each square mile of the earth’s surface,”245 a quantity which is, of course, quite insignificant.
According to Humboldt, Chladni states that a Franciscan monk was killed by the fall of an aërolite at Milan in the year 1660.246 Humboldt also mentions the death by meteoric stones of a monk at Crema on September 4, 1511, and two Swedish sailors on board ship in 1674.247
It is a curious fact that, according to Olbers, “no fossil meteoric stones” have ever been discovered.248 Considering the number which are supposed to have fallen to the earth in the course of ages, this fact seems a remarkable one.
On May 10, 1879, a shower of meteorites fell at Eitherville, Iowa (U.S.A.). Some of the fragments found weighed 437, 170, 92½, 28, 10½, 4 and 2 lbs. in weight. In the following year (1880) when the prairie grass had been consumed by a fire, about “5000 pieces were found from the size of a pin to a pound in weight.”249
According to Prof. Silvestria of Catania, a shower of meteoric dust mixed with rain fell on the night of March 29, 1880. The dust contained a large proportion of iron in the metallic state. In size the particles varied from a tenth to a hundredth of a millimetre.250
It is sometimes stated that the average mass of a “shooting star” is only a few grains. But from comparisons with an electric arc light, Prof. W. H. Pickering concludes that a meteor as bright as a third magnitude star, composed of iron or stone, would probably have a diameter of 6 or 7 inches. An average bright fireball would perhaps measure 5 or 6 feet in diameter.251
In the Book of Joshua we are told “that the Lord cast down great stones from heaven upon them unto Azekah, and they died” (Joshua x. 11). In the latter portion of the verse “hailstones” are mentioned, but as the original Hebrew word means stones in general (not hailstones), it seems very probable that the stones referred to were aërolites.252
The stone mentioned in the Acts of the Apostles, from which was found “the image which fell down from Jupiter” (Acts xix. 35), was evidently a meteoric stone.[253]
The famous stone in the Caaba at Mecca, is probably a stone of meteoric origin.[253]
I
“Stones from Heaven! Can you wonder,
You who scrutinize the Earth,
At the love and veneration
They received before the birth
Of our scientific methods?
II
“Stones from Heaven! we can handle
Fragments fallen from realms of Space;
Oh! the marvel and the mystery,
Could we understand their place
In the scheme of things created!
III
“Stones from Heaven! With a mighty
Comet whirling formed they part?
Fell they from their lofty station
Like a brilliant fiery dart,
Hurl’d from starry fields of Night?”253
CHAPTER XIII
The Zodiacal Light and Gegenschein
According to Gruson and Brugsch, the Zodiacal Light was known in ancient times, and was even worshipped by the Egyptians. Strabo does not mention it; but Diodorus Siculus seems to refer to it (B.C. 373), and he probably obtained his information from some Greek writers before his time, possibly from Zenophon, who lived in the sixth century B.C.254 Coming to the Christian era, it was noticed by Nicephorus, about 410 B.C. In the Koran, it is called the “false Aurora”; and it is supposed to be referred to in the “Rubáiyát” of Omar Khayyam, the Persian astronomical poet, in the second stanza of that poem (Edward Fitzgerald’s translation) —
“Dreaming when Dawn’s Left Hand was in the Sky,255
I heard a voice within the Tavern cry,
Awake, my Little ones, and fill the Cup,
Before Life’s Liquor in its Cup be dry.”
It was observed by Cassini in 1668,256 and by Hooke in 1705. A short description of its appearance will be found in Childrey’s Britannia Baconica (1661), p. 183.
The finest displays of this curious light seem to occur between the middle of January and the middle of February. In February, 1856, Secchi found it brighter than he had ever seen it before. It was yellowish towards the axis of the cone, and it seemed to be brighter than the Milky Way in Cygnus. He described it as “un grande spectacle.” In the middle of February, 1866, Mr. Lassell, during his last residence in Malta, saw a remarkable display of the Zodiacal Light. He found it at least twice as bright as the brightest part of the Milky Way, and much brighter than he had previously seen it. He found that the character of its light differed considerably from that of the Milky Way. It was of a much redder hue than the Galaxy. In 1874 very remarkable displays were seen in the neighbourhood of London in January and February of that year; and in 1875 on January 24, 25, and 30. On January 24 it was noticed that the “light” was distinctly reddish and much excelled in brightness any portion of the Milky Way.
Humboldt, who observed it from Andes (at a height of 13,000 to 15,000 feet), from Venezuela and from Cumana, tells us that he has seen the Zodiacal Light equal in brightness to the Milky Way in Sagittarius.
As probably many people have never seen the “light,” a caution may be given to those who care to look for it. It is defined by the Rev. George Jones, Chaplain to the “United States’ Japan Expedition” (1853-55), as “a brightness that appears in the western sky after sunset, and in the east before sunrise; following nearly or quite the line of the ecliptic in the heavens, and stretching upwards to various elevations according to the season of the year.” From the description some might suppose that the light is visible immediately after sunset. But this is not so; it never appears until twilight is over and “the night has fully set in.”
The “light” is usually seen after sunset or before sunrise. But attempts have recently been made by Prof. Simon Newcomb to observe it north of the sun. To avoid the effects of twilight the sun must be only slightly more than 18° below the horizon (that is, a little before or after the longest day). This condition limits the place of observation to latitudes not much south of 46°; and to reduce atmospheric absorption the observing station should be as high as possible above the level of the sea. Prof. Newcomb, observing from the Brienzer Rothorn in Switzerland (latitude 46° 47′ N., longitude 8° 3′ E.), succeeded in tracing the “light” to a distance of 35° north of the sun. It would seem, therefore, that the Zodiacal Light envelops the sun on all sides, but has a greater extension in the direction of the ecliptic.257 From observations at the Lick Observatory, Mr. E. A. Fath found an extension of 46° north of the sun.258
From observations of the “light” made by Prof. Barnard at the Yerkes Observatory during the summer of 1906, he finds that it extends to at least 65° north of the sun, a considerably higher value than that found by Prof. Newcomb.259 The difference may perhaps be explained by actual variation of the meteoric matter producing the light. Prof. J. H. Poynting thinks that possibly the Zodiacal Light is due to the “dust of long dead comets.”260
From careful observations of the “light,” Mr. Gavin J. Burns finds that its luminosity is “some 40 or 50 per cent. brighter than the background of the sky. Prof. Newcomb has made a precisely similar remark about the luminosity of the Milky Way, viz. that it is surprisingly small.” This agrees with my own observations during many years. It is only on the finest and clearest nights that the Milky Way forms a conspicuous object in the night sky. And this only in the country. The lights of a city almost entirely obliterate it. Mr. Burns finds that the Zodiacal Light appears “to be of a yellowish tint; or if we call it white, then the Milky Way is comparatively of a bluish tint.” During my residence in the Punjab the Zodiacal Light seemed to me constantly visible in the evening sky in the spring months. In the west of Ireland I have seen it nearly as bright as the brightest portions of the Milky Way visible in this country (February 20, 1890). The “meteoric theory” of the “light” seems to be the one now generally accepted by astronomers, and in this opinion I fully concur.
From observations made in Jamaica in the years 1899 and 1901, Mr. Maxwell Hall arrived at the conclusion that “the Zodiacal Light is caused by reflection of sunlight from masses of meteoric matter still contained in the invariable plane, which may be considered the original plane of the solar system.”261 According to Humboldt, Cassini believed that the Zodiacal Light “consisted of innumerably small planetary bodies revolving round the sun.”262
The Gegenschein, or Counter-glow. – This is a faint patch of light seen opposite the sun’s place in the sky, that is on the meridian at midnight. It is usually elliptical in shape, with its longer axis lying nearly in the plane of the ecliptic. It seems to have been first detected by Brorsen (the discoverer of the short-period comet of 1846) about the middle of the nineteenth century. But it is not easy to see, for the famous Heis of Münster, who had very keen eyesight, did not succeed in seeing it for several years after Brorsen’s announcement.263 It was afterwards independently discovered by Backhouse, and Barnard.
Prof. Barnard’s earlier observations seemed to show that the Gegenschein does not lie exactly opposite to the sun, but very nearly so. He found its longitude is within one degree of 180°, and its latitude about 1°·3 north of the ecliptic.264 But from subsequent observations he came to the conclusion that the differences in longitude and apparent latitude are due to atmospheric absorption, and that the object really lies in the ecliptic and exactly opposite to the sun.265
Barnard finds that the Gegenschein is not so faint as is generally supposed. He says “it is best seen by averted vision, the face being turned 60° or 70° to the right or left, and the eyes alone turned towards it.” It is invisible in June and December, while in September it is round, with a diameter of 20°, and very distinct. No satisfactory theory has yet been advanced to account for this curious phenomenon. Prof. Arthur Searle of Harvard attributes it to a number of asteroids too small to be seen individually. When in “opposition” to the sun these would be fully illuminated and nearest to the earth. Its distance from the earth probably exceeds that of the moon. Dr. Johnson Stoney thinks that the Gegenschein may possibly be due to a “tail” of hydrogen and helium gases repelled from the earth by solar action; this “tail” being visible to us by reflected sunlight.
It was observed under favourable circumstances in January and February, 1903, by the French astronomer, M. F. Quénisset. He found that it was better seen when the atmosphere was less clear, contrary to his experience of the Zodiacal Light. Prof. Barnard’s experience confirms this. M. Quénisset notes that – as in the case of the Zodiacal Light – the southern border of the Gegenschein is sharper than the northern. He found that its brightness is less than that of the Milky Way between Betelgeuse and γ Geminorum; and thinks that it is merely a strengthening of the Zodiacal Light.266
A meteoritic theory of the Gegenschein has been advanced by Prof. F. R. Moulton, which explains it by light reflected from a swarm of meteorites revolving round the sun at a distance of 930,240 miles outside the earth’s orbit.
Both the Zodiacal Light and Gegenschein were observed by Herr Leo Brenner on the evening of March 4, 1896. He found the Zodiacal Light on this evening to be “perhaps eight times brighter than the Milky Way in Perseus.” The “Gegenschein distinctly visible as a round, bright, cloud-like nebula below Leo (Virgo), and about twice the brightness of the Milky Way in Monoceros between Canis Major and Canis Minor.”267
Humboldt thought that the fluctuations in the brilliancy of the Zodiacal Light were probably due to a real variation in the intensity of the phenomenon rather than to the elevated position of the observer.268 He says that he was “astonished in the tropical climates of South America, to observe the variable intensity of the light.”