Astronomical Curiosities Part 2

On the whole the occasional illumination of the night side of Venus by a very brilliant aurora (explanation (4) above) seems to the present writer to be the most probable explanation. Gruithuisen's hypothesis (7) seems utterly improbable.

There is a curious apparent anomaly about the motion of Venus in the sky.

Although the planet's period of revolution round the sun is 2247 days, it remains on the same side of the sun, as seen from the earth, for 290 days.

The reason of this is that the earth is going at the same time round the sun in the same direction, though at a slower pace; and Venus must continue to appear on the same side of the sun until the excess of her daily motion above that of the earth amounts to 179, and this at the daily rate of 37' will be about 290 days.

Several observations have been recorded of a supposed satellite of Venus.

But the existence of such a body has never been verified. In the year 1887, M. Stroobant investigated the various accounts, and came to the conclusion that in several at least of the recorded observations the object seen was certainly a star. Thus, in the observation made by Rd.i.c.kr and Boserup on August 4, 1761, a satellite and star are recorded as having been seen near the planet. M. Stroobant finds that the supposed "satellite" was the star ?_{4} Orionis, and the "star" ?_{3} Orionis. A supposed observation of a satellite made by Horrebow on January 3, 1768, was undoubtedly ? Librae. M. Stroobant found that the supposed motion of the "satellite" as seen by Horrebow is accurately represented by the motion of Venus itself during the time of observation. In most of the other supposed observations of a satellite a satisfactory identification has also been found. M. Stroobant finds that with a telescope of 6 inches aperture, a star of the 8th or even the 9th magnitude can be well seen when close to Venus.[49]

On the night of August 13, 1892, Professor Barnard, while examining Venus with the great 36-inch telescope of the Lick Observatory, saw a star of the 7th magnitude in the same field with the planet. He carefully determined the exact position of this star, and found that it is not in Argelander's great catalogue, the _Durchmusterung_. Prof. Barnard finds that owing to elongation of Venus from the sun at the time of observation the star could not possibly be an intra-Mercurial planet (that is, a planet revolving round the sun inside the orbit of Mercury); but that possibly it might be a planet revolving between the orbits of Venus and Mercury. As the brightest of the minor planets--Ceres, Pallas, Juno, and Vesta--were not at the time near the position of the observed object, the observation remains unexplained. It might possibly have been a _nova_, or temporary star.[50]

Scheuten is said to have seen a supposed satellite of Venus following the planet across the sun at the end of the transit of June 6, 1761.[51]

Humboldt speaks of the supposed satellite of Venus as among "the astronomical myths of an uncritical age."[52]

An occultation of Venus by the moon is mentioned in the Chinese Annals as having occurred on March 19, 361 A.D., and Tycho Brahe observed another on May 23, 1587.[53]

A close conjunction of Venus and Regulus (a Leonis) is recorded by the Arabian astronomer, Ibn Yunis, as having occurred on September 9, 885 A.D.

Calculations by Hind show that the planet and star were within 2' of arc on that night, and consequently would have appeared as a single star to the naked eye. The telescope had not then been invented.[54]

Seen from Venus, the maximum apparent distance between the earth and moon would vary from about 5' to 31'.[55]

It is related by Arago that Buonaparte, when going to the Luxembourg in Paris, where the Directory were giving a fete in his honour, was very much surprised to find the crowd a.s.sembled in the Rue de Touracour "pay more attention to a region of the heavens situated above the palace than to his person or the brilliant staff that accompanied him. He inquired the cause and learned that these curious persons were observing with astonishment, although it was noon, a star, which they supposed to be that of the conqueror of Italy--an allusion to which the ill.u.s.trious general did not seem indifferent, when he himself, with his piercing eyes, remarked the radiant body." The "star" in question was Venus.[56]

CHAPTER IV

The Earth

The earth being our place of abode is, of course, to us the most important planet in the solar system. It is a curious paradox that the moon's surface (at least the visible portion) is better known to us than the surface of the earth. Every spot on the moon's visible surface equal in size to say Liverpool or Glasgow is well known to lunar observers, whereas there are thousands of square miles on the earth's surface--for example, near the poles and in the centre of Australia--which are wholly unknown to the earth's inhabitants; and are perhaps likely to remain so.

Many attempts have been made by "paradoxers" to show that the earth is a flat plane and not a sphere. But M. Ricco has found by actual experiment that the reflected image of the setting sun from a smooth sea is an elongated ellipse. This proves mathematically beyond all doubt that the surface of the sea is spherical; for the reflection from a plane surface would be necessarily _circular_. The theory of a "flat earth" is therefore proved to be quite untenable, and all the arguments (?) of the "earth flatteners" have now been--like the French Revolution--"blown into s.p.a.ce."

The pole of minimum temperature in the northern hemisphere, or "the pole of cold," as it has been termed, is supposed to lie near Werchojansk in Siberia, where a temperature of nearly -70 has been observed.

From a series of observations made at Annapolis (U.S.A.) on the gradual disappearance of the blue of the sky after sunset, Dr. See finds that the extreme height of the earth's atmosphere is about 130 miles. Prof. Newcomb finds that meteors first appear at a mean height of about 74 miles.[57]

An aurora seen in Canada on July 15, 1893, was observed from stations 110 miles apart, and from these observations the aurora was found to lie at a height of 166 miles above the earth's surface. It was computed that if the auroral "arch maintained an equal height above the earth its ends were 1150 miles away, so that the magnificent sight was presented of an auroral belt in the sky with 2300 miles between its two extremities."[58]

"Luminous clouds" are bright clouds sometimes seen at night near the end of June and beginning of July. They appear above the northern horizon over the sun's place about midnight, and evidently lie at a great height above the earth's surface. Observations made in Germany by Dr. Jesse, and in England by Mr. Backhouse, in the years 1885-91, show that the height of these clouds is nearly constant at about 51 miles.[59] The present writer has seen these remarkable clouds on one or two occasions in County Sligo, Ireland, during the period above mentioned.

M. Montigny has shown that "the approach of violent cyclones or other storms is heralded by an increase of scintillation" (or twinkling of the stars). The effect is also very evident when such storms pa.s.s at a considerable distance. He has also made some interesting observations (especially on the star Capella), which show that, not only does scintillation increase in rainy weather, but that "it is very evident, at such times, in stars situated at an alt.i.tude at which on other occasions it would not be perceptible at all; thus confirming the remark of Humboldt's with regard to the advent of the wet season in tropical countries."[60]

In a paper on the subject of "Optical Illusions" in _Popular Astronomy_, February, 1906, Mr. Arthur K. Bartlett, of Batter Creek, Michigan (U.S.A.), makes the following interesting remarks:--

"The lunar halo which by many persons is regarded as a remarkable and unexplained luminosity a.s.sociated with the moon, is to meteorological students neither a mysterious nor an anomalous occurrence. It has been frequently observed and for many years thoroughly understood, and at the present time admits of an easy scientific explanation. It is an atmospheric exhibition due to the refraction and dispersion of the moon's light through very minute ice crystals floating at great elevations above the earth, and it is explained by the science of meteorology, to which it properly belongs; for it is not of cosmical origin, and in no way pertains to astronomy, as most persons suppose, except as it depends on the moon, whose light pa.s.sing through the atmosphere, produces the luminous halo, which as will be seen, is simply an optical illusion, originating, not in the vicinity of the moon--two hundred and forty thousand miles away--but just above the earth's surface, and within the aqueous envelope that surrounds it on all sides.... A halo may form round the sun as well as the moon ...

but a halo is more frequently noticed round the moon for the reason that we are too much dazzled by the sun's light to distinguish faint colours surrounding its disc, and to see them it is necessary to look through smoked gla.s.s, or view the sun by reflection from the surface of still water, by which its brilliancy is very much reduced."...

"A 'corona' is an appearance of faintly coloured rings often seen around the sun and moon when a light fleecy cloud pa.s.ses over them, and should not be mistaken for a halo, which is much larger and more complicated in its structure. These two phenomena are frequently confounded by inexperienced observers." With these remarks the present writer fully concurs.

Mr. Bartlett adds--

"As a halo is never seen except when the sky is hazy, it indicates that moisture is acc.u.mulating in the atmosphere which will form clouds, and usually result in a storm. But the popular notion that the number of bright stars visible within the circle indicates the number of days before the storm will occur, is without any foundation whatever, and the belief is almost too absurd to be refuted. In whatever part of the sky a lunar halo is seen, one or more bright stars are always sure to be noticed inside the luminous ring, and the number visible depends entirely upon the position of the moon.

Moreover, when the sky within the circle is examined with even a small telescope, hundreds of stars are visible where only one, or perhaps two or three, are perceived with the naked eye."

It is possible to have five Sundays in February (the year must of course be a "leap year"). This occurred in the year 1880, Sunday falling on February 1, 8, 15, 22, and 29. But this will not happen again till the year 1920. No century year (such as 1900, 2000, etc.) could possibly have five Sundays in February, and the Rev. Richard Campbell, who investigated this matter, finds the following sequence of years in which five Sundays occur in February: 1604, 1632, 1660, 1688, 1728, 1756, 1784, 1824, 1852, 1880, 1920, 1948, 1976.[61]

In an article on "The Last Day and Year of the Century: Remarks on Time Reckoning," in _Nature_, September 10, 1896, Mr. W. T. Lynn, the eminent astronomer, says, "The late Astronomer Royal, Sir George Airy, once received a letter requesting him to settle a dispute which had arisen in some local debating society, as to which would be the first day of the next century. His reply was, 'A very little consideration will suffice to show that the first day of the twentieth century will be January 1, 1901.'

Simple as the matter seems, the fact that it is occasionally brought into question shows that there is some little difficulty connected with it.

Probably, however, this is in a great measure due to the circ.u.mstance that the actual figures are changed on January 1, 1900, the day preceding being December 31, 1899. A century is a very definite word for an interval respecting which there is no possible room for mistake or difference of opinion. But the date of its ending depends upon that of its beginning.

Our double system of backward and forward reckoning leads to a good deal of inconvenience. Our reckoning supposes (what we know was not the case, but as an era the date does equally well) that Christ was born at the end of B.C. 1. At the end of A.D. 1, therefore, one year had elapsed from the event, at the end of A.D. 100, one century, and at the end of 1900, nineteen centuries.... It is clear, then, that the year, as we call it, is an ordinal number, and that 1900 years from the birth of Christ (reckoning as we do from B.C. 1) will not be completed until the end of December 31 in that year, the twentieth century beginning with January 1, 1901, that is (to be exact) at the previous midnight, when the day commences by civil reckoning." With these remarks of Mr. Lynn I fully concur, and, so far as I know, all astronomers agree with him. As the discussion will probably again arise at the end of the twentieth century, I would like to put on record here what the scientific opinion was at the close of the nineteenth century.

Prof. E. Rutherford, the well-known authority on radium, suggests that possibly radium is a source of heat from within the earth. Traces of radium have been detected in many rocks and soils, and even in sea water.

Calculation shows that the total amount distributed through the earth's crust is enormously large, although relatively small "compared with the annual output of coal for the world." The amount of radium necessary to compensate for the present loss of heat from the earth "corresponds to only five parts in one hundred million millions per unit ma.s.s," and the "observations of Elster and Gertel show that the radio-activity observed in soils corresponds to the presence of about this proportion of radium."[62]

The earth has 12 different motions. These are as follows:--

1. Rotation on its axis, having a period of 24 hours.

2. Revolution round the sun; period 365 days.

3. Precession; period of about 25,765 years.

4. Semi-lunar gravitation; period 28 days.

5. Nutation; period 18 years.

6. Variation in obliquity of the ecliptic; about 47" in 100 years.

7. Variation of eccentricity of orbit.

8. Change of line of apsides; period about 21,000 years.

9. Planetary perturbations.

10. Change of centre of gravity of whole solar system.

11. General motion of solar system in s.p.a.ce.

12. Variation of lat.i.tude with several degrees of periodicity.[63]

"An amusing story has been told which affords a good ill.u.s.tration of the ignorance and popular notions regarding the tides prevailing even among persons of average intelligence. 'Tell me,' said a man to an eminent living English astronomer not long ago, 'is it still considered probable that the tides are caused by the moon?' The man of science replied that to the best of his belief it was, and then asked in turn whether the inquirer had any serious reason for questioning the relations.h.i.+p. 'Well, I don't know,' was the answer; 'sometimes when there is no moon there seems to be a tide all the same.'"![64]

With reference to the force of gravitation, on the earth and other bodies in the universe, Mr. William B. Taylor has well said, "With each revolving year new demonstrations of its absolute precision and of its universal domination serves only to fill the mind with added wonder and with added confidence in the stability and the supremacy of the power in which has been found no variableness neither shadow of turning, but which--the same yesterday, to-day and for ever--

"Lives through all life, extends through all extent, Spreads undivided, operates unspent."[65]