Sun spotPortion of the Sun’s Surface. Sunspot nearly 60,000 Miles Across
Portion of the Sun’s Surface. Sunspot nearly 60,000 Miles Across
It is a curious fact that Al-Sûfi, the Persian astronomer, in hisDescription of the Heavens, written in the Tenth Century, speaks distinctly of Algol as a red star (étoile,brillant;d’un éclat,rouge), while at present it is white or at the most of a yellowcolor. A similar change of color is supposed to have taken place in the case of Sirius, but the change in Algol seems more certain, as Al-Sûfi’s descriptions are generally most accurate and reliable.
Stars of the Algol type of variable are very rare objects, only a dozen or so having been hitherto discovered in the whole heavens. Those visible to the naked eye, when at their normal brightness, are: Algol, Lambda Tauri, Delta Libræ, R Canis Majoris, and U Ophiuchi.
A remarkable peculiarity about the variable stars in general is that none of them has any considerable proper motion. As a large proper motion is generally considered to indicate proximity to the earth, we may conclude, with great probability, that the variable stars, as a rule, lie at a great distance from our system. In other words, it appears that the sun does not lie in a region of variable stars, and, with the exception of Alpha Cassiopeiæ and Alpha Herculis, a measurable parallax has not yet been found, so far as I know, for any known variable star.
We now come to the interesting and mysterious class of objects known as “new” or “temporary” stars. These phenomena are of very rare occurrence, and but few undoubted examples of the class are recorded in the annals of astronomy. Possibly in some cases they have been merely variable stars, of irregular period and fitful variability; but others may have been due to a real catastrophe, such as the collision of two dark bodies in space, or, possibly, the passage of a bright or dark body through a gaseous nebula.
The earliest temporary star of which we have any reliable information seems to be one which is recorded in the Chinese annals of Ma-tuan-lin, as having appeared in the year 134B. C.in the constellation Scorpio. Its position seems to have been somewhere between the stars Beta and Rho of Scorpio. Pliny informs us that it was the sudden appearance of a new star which induced the famous astronomer Hipparchus to form his catalogue of stars, the first ever constructed. As the date of Hipparchus’s catalogue is 125B. C., it seems highly probable that the new star referred to by Pliny was the same as that recorded by the Chinese astronomer as having appeared nine years previously.
A new star is said to have appeared in the year 76B. C.between the stars Alpha and Delta in the Plow, but the accounts are vague.
In 101A. D., a small “yellowish-blue” star is said to have appeared in the “sickle” in Leo, but its exact position is not known. In 107A. D., a new star is mentioned near Delta, Epsilon and Eta in Canis Major, three bright stars southeast of Sirius. In 123A. D., another new star is recorded by Ma-tuan-lin to have appeared between Alpha Herculis and Alpha Ophiuchi.
The Chinese annals record that on December 10, 173A. D., a brilliant star appeared between Alpha and Beta Centauri in the Southern Hemisphere. It remained visible for eight months, and is described as resembling “a large bamboo mat!”—a curious description. There is at present, close to the spot indicated, a known variable star—R Centauri—ofwhich the period seems to be long and the variation of light irregular. Possibly an unusually bright maximum of this variable star formed the star of the Chinese annals, or perhaps the variable star is the remnant of the outburst which took place in the First Century. The variable is a very reddish star, and at present varies from about the sixth to the tenth magnitude.
A new star is recorded in the year 386A. D.as having appeared between Lambda and Phi Sagittarii. Near the position indicated, Flamsteed observed a star, No. 65 of his catalogue, which is now missing; and it has been conjectured that the star seen by Flamsteed may possibly have been a return of the star mentioned in the Chinese annals.
Cuspianus relates that a star as bright as Venus appeared near Altair in 389A. D., during the reign of the Emperor Honorius, and that he had himself seen it. There is some doubt, however, about the exact date, as other accounts give the year 388 or 398. The star seems to have disappeared in about three weeks.
In the year 393A. D., another strange star is recorded in the tail of Scorpio. An extraordinary star is said to have been seen near Alpha Crateris in 561A. D.Here again a known variable and red star—R Crateris—is close to the position indicated by the ancient records.
The Chinese annals record a new star in 829A. D., somewhere in the vicinity of the bright star Procyon, and in this locality there are several known variable stars.
The Bohemian astronomer, Cyprianus Leoviticus, mentions the appearance of new stars in Cassiopeia in the years 945A. D.and 1264, and it has been conjectured that perhaps these were apparitions of Tycho Brahe’s famous star of 1572 (to be presently described), forming a variable star with a period of over 300 years. Lynn and Sadler, however, have shown that the supposed stars of 945 and 1264 were, in all probability, comets.
Extraordinary stars are recorded near Zeta Sagittarii in 1011A. D., near Mu Scorpii in 1203, and near Pi Scorpii on July 1, 1584. It is remarkable how many of these objects seem to have appeared in this portion of the heavens.
A very brilliant star is mentioned by Hepidannus as having appeared in Aries in May, 1012. He describes it as “dazzling the eye.” Other temporary stars are mentioned in 1054A. D., near Zeta Tauri, and in 1139 near Kappa Virginis; but the accounts of these are very vague, and it seems by no means certain that they were really new stars.
No possible doubt, however, can be entertained with reference to the appearance of the object which suddenly blazed out in Cassiopeia’s Chair in November, 1572. It was called the “Pilgrim Star,” and was observed by the famous astronomer, Tycho Brahe, who has left us a very elaborate account of its appearance, position, etc. Although usually spoken of as Tycho Brahe’s star, it seems to have been really discovered by Cornelius Gemma on the evening of November 9. That its appearance was very suddenmay be inferredfrom Cornelius Gemma’sstatement that it was not visible on the preceding night in a clear sky. Tycho Brahe’s attention was first attracted to it on November 11. His description of the new star is as follows—as quoted by Humboldt: “On my return to the Danish islands from my travels in Germany, I resided for some time with my uncle, Steno Bille, in the old and pleasantly situated monastery of Herritzwadt, and here I made it a practice not to leave my chemical laboratory until the evening. Raising my eyes, as usual, during one of my walks, to the well-known vault of heaven, I observed with indescribable astonishment, near the zenith in Cassiopeia, a radiant fixed star of a magnitude never before seen. In my amazement, I doubted the evidence of my senses. However, to convince myself that it was no illusion, and to have the testimony of others, I summoned my assistants from the laboratory, and inquired of them, and of all the country people that passed by, if they also observed the star that had thus suddenly burst forth. I subsequently heard that in Germany, wagoners and other common people first called the attention of astronomers to this great phenomenon in the heavens—a circumstance which, as in the case of non-predicted comets, furnished fresh occasion for the usual raillery at the expense of the learned. This new star I found to be without a tail, not surrounded by any nebula, and perfectly like all other fixed stars, with the exception that it scintillated more strongly than stars of the first magnitude. Its brightness was greater than that of Sirius, Alpha Lyræ, or Jupiter. For splendor, it was only comparable to Venus whennearest to earth (that is, when only a quarter of her disk is illuminated). Those gifted with keen sight could, when the air was clear, discern the new star in the daytime, and even at noon. At night, when the sky was overcast, so that all other stars were hidden, it was often visible through the clouds, if they were not very dense (nubes non admodum densas). Its distances from the nearest stars of Cassiopeia, which throughout the whole of the following year I measured with great care, convinced me of its perfect immobility. Already in December, 1572, its brilliancy began to diminish, and the star gradually resembled Jupiter, but by January, 1573, it had become less bright than that planet. Toward the month of November the new star was not brighter than the eleventh in the lower part of Cassiopeia’s Chair. The transition to the fifth and sixth magnitudes took place between December, 1573, and February, 1574. In the following month the new star disappeared, and, after having shone seventeen months, was no longer discernible to the naked eye.” (The telescope was not invented until thirty-seven years afterward.) Humboldt adds: “At its first appearance, as long as it had the brilliancy of Venus and Jupiter, it was for two months white, and then passed through yellow into red. In the spring of 1573, Tycho Brahe compared it to Mars; afterward he thought it nearly resembled Betelgeuse, the star in the right shoulder of Orion. The color for the most part was like the red tint of Aldebaran. In the spring of 1573, and especially in May, its white color returned (albedinam quandam sublividam induebat,qualis Saturni stellæ subesse videtur). So it remained in January, 1574; being, up to the time of its entire disappearance in the month of March, 1574, of the fifth magnitude, and white, but of a duller whiteness, and exhibiting a remarkably strong scintillation in proportion to its faintness.”
Ma-tuan-lin speaks of a star in 1578 “as large as the sun” (!) but does not state its position.
The star known as P (34) Cygni is sometimes spoken of as a “Nova,” or new star; but it is still visible to the naked eye as a star of the fifth magnitude. It was observed of the third magnitude by Jansen in 1600 and by Kepler in 1602. After the year 1619 it appears to have diminished in brightness, and is said to have vanished in 1621; but it may merely have become too faint to be seen with the naked eye. It was again observed of the third magnitude by Dominique Cassini in 1655, and it afterward disappeared. It was again seen by Hevelius in November, 1655. In 1667, 1682, and 1715 it is recorded as of the sixth magnitude, and there is no further record of any marked increase in its light. A period of about 18 years was assumed by Pigott; but this is now disproved, and it seems probable that the star is a variable of irregular period and fitful variability, and not, properly speaking, a temporary star. Its present color is yellow, and bright lines have been seen in its spectrum.
A new star of the third magnitude was observed near Beta Cygni by the Carthusian monk Anthelmus in 1670. It remained visible for about two years, and is said to have increased and diminished severaltimes before its final disappearance. Schönfeld computed its exact position from observations made by Hevelius and Picard. Quite close to the spot indicated, a star of the eleventh magnitude has been observed at the Greenwich Observatory, and fluctuations of light were suspected in this small star by Hind and others.
A very remarkable star, sometimes called the “Blaze Star,” suddenly appeared in Corona Borealis, in May, 1866. It was first seen by the late Mr. Birmingham, at Tuam, Ireland, about midnight on the evening of May 12, when it was of the second magnitude, and equal to Alphecca, “the gem of the coronet.” Its appearance must have been very sudden, for Schmidt, the Director of the Athens Observatory, stated that he was observing the constellation on the same evening, about two and one-half hours previous to Birmingham’s discovery, and observed nothing unusual. He was certain that no star, of even the fifth magnitude, could possibly have escaped his notice. On the following night it was seen by several observers in different parts of the world.
A remarkable and very interesting temporary star was discovered in 1892 in the constellation Auriga.
It is a remarkable fact that the great majority of the temporary stars appeared in or near the Milky Way. The chief exceptions to this rule are: the star of 76B. C., in the Plow, the star recorded by Hepidannus in Aries, 1012A. D., and the “Blaze Star” of 1866 in Corona Borealis.