Astronomical Curiosities: Facts and Fallacies

Prof. Barnard has suggested that all the phenomena of comets’ tails cannot be explained by a repulsive force from the sun. Short tails issuing from the comet’s nucleus at considerable angles with the main tail point to eruptive action in the comet itself. The rapid changes and distortions frequently observed in the tails of some comets suggest motion through a resisting medium; and the sudden increase of light also occasionally observed points in the same direction.198

It was computed by Olbers that if a comet having a mass of 1⁄2000th of the earth’s mass – which would form a globe of about 520 miles in diameter and of the density of granite – collided with the earth, with a velocity of 40 miles a second, our globe would be shattered into fragments.199 But that any comet has a solid nucleus of this size seems very doubtful; and we may further say that the collision of the earth with any comet is highly improbable.

It seems to be a common idea that harvests are affected by comets, and even “comet wines” are sometimes spoken of. But we know that the earth receives practically no heat from the brightest comet. Even in the case of the brilliant comet of 1811, one of the finest on record, it was found that “all the efforts to concentrate its rays did not produce the slightest effect on the blackened bulb of the most sensitive thermometer.” Arago found that the year 1808, in which several comets were visible, was a cold year, “and 1831, in which there was no comet, enjoyed a much higher temperature than 1819, when there were three comets, one of which was very brilliant.”200 We may, therefore, safely conclude that even a large comet has no effect whatever on the weather.

From calculations on the orbit of Halley’s comet, the next return of which is due in 1910, Messrs. Cowell and Crommelin find that the identity of the comet shown on the Bayeux Tapestry with Halley’s comet is now “fully established.” They find that the date of perihelion passage was March 25, 1066, which differs by only 4 days from the date found by Hind. The imposing aspect of the comet in 1066 described in European chronicles of that time is confirmed by the Chinese Annals. In the latter records the brightness is compared to that of Venus, and even with that of the moon! The comparison with the moon was probably an exaggeration, but the comet doubtless made a very brilliant show. In the Bayeux Tapestry the inscription on the wall behind the spectators reads: “isti mirant stella.” Now, this is bad Latin, and Mr. W. T. Lynn has made the interesting suggestion that some of the letters are hidden by the buildings in front and that the real sentence is “isti mirantur stellam.”201 The present writer has examined the copy of the Bayeux Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn’s suggestion seems very plausible. But the last letter of stellam is apparently hidden by the comet’s tail, which does not seem very probable!

The conditions under which the comet will appear in 1910 are not unlike those of 1066 and 1145. “In each year the comet was discovered as a morning star, then lost in the sun’s rays; on its emergence it was near the earth and moved with great rapidity, finally becoming stationary in the neighbourhood of Hydra, where it was lost to view.”202 In 1910 it will probably be an evening star before March 17, and after May 11, making a near approach to the earth about May 12. About this time its apparent motion in the sky will be very rapid. As, however, periodical comets – such as Halley’s – seem to become fainter at each return, great expectations with reference to its appearance in 1910 should not be indulged in.

The appearance of Halley’s comet in A.D. 1222 is thus described by Pingré – a great authority on comets – (quoting from an ancient writer) —

“In autumn, that is to say in the months of August and September, a star of the first magnitude was seen, very red, and accompanied by a great tail which extended towards the top of the sky in the form of a cone extremely pointed. It appeared to be very near the earth. It was observed (at first?) near the place of the setting sun in the month of December.”

With reference to its appearance in the year 1456, when it was of “vivid brightness,” and had a tail of 60° in length, Admiral Smyth says,203 “To its malign influence were imputed the rapid successes of Mahomet II., which then threatened all Christendom. The general alarm was greatly aggravated by the conduct of Pope Callixtus III., who, though otherwise a man of abilities, was a poor astronomer; for that pontiff daily ordered the church bells to be rung at noon-tide, extra Ave-Marias to be repeated, and a special protest and excommunication was composed, exorcising equally the Devil, the Turks, and the comet.” With reference to this story, Mr. G. F. Chambers points out204 that it is probably based on a passage in Platina’s Vitæ Pontificum. But in this passage there is no mention made of excommunication or exorcism, so that the story, which has long been current, is probably mythical. In confirmation of this view, the Rev. W. F. Rigge has shown conclusively205 that no bull was ever issued by Pope Callixtus III. containing a reference to any comet. The story would therefore seem to be absolutely without foundation, and should be consigned to the limbo of all such baseless myths.

With reference to the appearance of Halley’s comet, at his last return in 1835, Sir John Herschel, who observed it at the Cape of Good Hope, says —

“Among the innumerable stars of all magnitudes, from the ninth downwards, which at various times were seen through it, and some extremely near to the nucleus (though not exactly on it) there never appeared the least ground for presuming any extinction of their light in traversing it. Very minute stars indeed, on entering its brightest portions, were obliterated, as they would have been by an equal illumination of the field of view; but stars which before their entry appeared bright enough to bear that degree of illumination, were in no case, so far as I could judge, affected to a greater extent than they would have been by so much lamp-light artificially introduced.”206

It is computed by Prof. J. Holetschak that, early in October, 1909, Halley’s comet should have the brightness of a star of about 14½ magnitude.207 It should then – if not detected before – be discoverable with some of the large telescopes now available.

According to the computations of Messrs. Cowell and Crommelin, the comet should enter Pisces from Aries in January, 1910. “Travelling westward towards the star γ Piscium until the beginning of May, and then turning eastward again, it will travel back through the constellations Cetus, Orion, Monoceros, Hydra, and Sextans.” From this it seems that observers in the southern hemisphere will have a better view of the comet than those in northern latitudes. The computed brightness varies from 1 on January 2, 1910, to 1112 on May 10. But the actual brightness of a comet does not always agree with theory. It is sometimes brighter than calculation would indicate.

According to Prof. O. C. Wendell, Halley’s comet will, on May 12, 1910, approach the earth’s orbit within 4·6 millions of miles; and he thinks that possibly the earth may “encounter some meteors,” which are presumably connected with the comet. He has computed the “radiant point” of these meteors (that is, the point from which they appear to come), and finds its position to be R.A. 22h 42m·9, Decl. N. 1° 18′. This point lies a little south-west of the star β Piscium.

According to Dr. Smart, the comet will, on June 2, “cross the Equator thirteen degrees south of Regulus, and will then move slowly in the direction of φ Leonis. The comet will be at its descending node on the ecliptic in the morning of May 16, and the earth will pass through the node on the comet’s orbit about two and a half days later. The comet’s orbit at the node is about 13 million miles within that of the earth. Matter repelled from the comet’s nucleus by the sun with a velocity of about 216,000 miles per hour, would just meet the earth when crossing the comet’s orbit plane. Matter expelled with a velocity of 80,000 miles per hour, as in the case of Comet Morehouse, would require seven days for the journey. Cometary matter is said to have acquired greater velocities than this, for (according to Webb, who quotes Chacornac) Comet II., 1862, shot luminous matter towards the sun, with a velocity of nearly 2200 miles per second. It is therefore possible that matter thrown off by the comet at the node may enter our atmosphere, in which case we must hope that cyanogen, which so often appears in cometary spectra, may not be inconveniently in evidence.”208

Cyanogen is, of course, a poisonous gas, but cometary matter is so rarefied that injurious effects on the earth need not be feared.

If we can believe the accounts which have been handed down to us, some very wonderful comets were visible in ancient times. The following may be mentioned: —

B.C. 165. The sun is said to have been “seen for several hours in the night.” If this was a comet it must have been one of extraordinary brilliancy.209

B.C. 146. “After the death of Demetrius, king of Syria, the father of Demetrius and Antiochus, a little before the war in Achaia, there appeared a comet as large as the sun. Its disc was first red, and like fire, spreading sufficient light to dissipate the darkness of night; after a little while its size diminished, its brilliancy became weakened, and at length it entirely disappeared.”210

B.C. 134. It is recorded that at the birth of Mithridates a great comet appeared which “occupied the fourth part of the sky, and its brilliancy was superior to that of the sun.” (?)211

B.C. 75. A comet is described as equal in size to the moon, and giving as much light as the sun on a cloudy day. (!)212

A.D. 531. In this year a great comet was observed in Europe and China. It is described as “a very large and fearful comet,” and was visible in the west for three weeks. Hind thinks that this was an appearance of Halley’s comet,213 and this has been confirmed by Mr. Crommelin.

A.D. 813, August 4. A comet is said to have appeared on this date, of which the following curious description is given: “It resembled two moons joined together; they separated, and having taken different forms, at length appeared like a man without a head.” (!)214

A.D. 893. A great comet is said to have appeared in this year with a tail 100° in length, which afterwards increased to 200°!215

A.D. 1402. A comet appeared in February of this year, which was visible in daylight for eight days. “On Palm Sunday, March 19, its size was prodigious.” Another comet, visible in the daytime, was seen from June to September of the same year.

When the orbit of the comet known as 1889 V was computed, it was found that it had passed through Jupiter’s system in 1886 (July 18-21). The calculations show that it must have passed within a distance of 112,300 miles of the planet itself – or less than half the moon’s distance from the earth – and “its centre may possibly have grazed the surface of Jupiter.”216

Sir John Herschel thought that the great comet of 1861 was by far the brightest comet he had ever seen, those of 1811 and 1858 (Donati’s) not excepted.217 Prof. Kreutz found its period of revolution round the sun to be about 409 years, with the plane of the orbit nearly at right angles to the plane of the ecliptic.

On November 9, 1795, Sir William Herschel saw the comet of that year pass centrally over a small double star of the 11th and 12th magnitudes, and the fainter of the two components remained distinctly visible during the comet’s transit over the star. This comet was an appearance of the comet now known as Encke’s.218 Struve saw a star of the 10th magnitude through nearly the brightest part of Encke’s comet on November 7, 1828, but the star’s light was not dimmed by the comet.

Sir John Herschel saw a cluster of stars of the 16th or 17th magnitude through Biela’s comet, although the interposed cometary matter must have been at least 50,000 miles in thickness.219

Bessel found that on September 29, 1835, a star of the 10th magnitude shone with undimmed lustre through the tail of Halley’s comet within 8 seconds of arc of the central point of the head. At Dorpat (Russia) Struve saw the same star “in conjunction only 2″·2 from the brightest point of the comet. The star remained continuously visible, and its light was not perceptibly diminished whilst the nucleus of the comet seemed to be almost extinguished before the radiance of the small star of the 9th or 10th magnitude.”220

Webb says —

“Donati saw a 7 mg. star enlarged so as to show a sensible disc, when the nucleus of comet III., 1860, passed very near it. Stars are said to have started, or become tremulous, during occultations by comets. Birmingham observed the comet of Encke illuminated by a star over which it passed, August 23, 1868; and Klein, in 1861, remarked an exceptional twinkling in 5 mg. stars involved in the tail.”221

The comet of 1729 had the greatest perihelion distance of any known comet;222 that is, when nearest to the sun, it did not approach the central luminary within four times the earth’s distance from the sun!

Barnard’s comet, 1889 I., although it never became visible to the naked eye, was visible with a telescope from September 2, 1888, to August 18, 1890, or 715 days – the longest period of visibility of any comet on record. When last seen it was 6¼ times the earth’s distance from the sun, or about 580 millions of miles,223 or beyond the orbit of Jupiter!

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.