Andrew Cooper
Feb 24, 2020    Waikoloa, HI (map)
20cm f/6 Newtonian, Cave Astrola @ 307x
Seeing: 7 Transparency: 7 Moon: 0%

Overwhelmingly brilliant, blue-white, dazzling light the drowns everything else in the field, attempted to see Sirius B without success using the 4mm and 307x, currently at about 10" should be possible with better seeing

Captain William Henry Smyth
Oct 19, 1835    No. 6 The Crescent, Bedford, England (map)
150mm f/17.6 refractor by Tully 1827

A standard Greenwich star, with a distant companion, in the Greater Dog's mouth. A 1, brilliant white; B 10, deep yellow, other distant small stars in the field; and a line through the two here cited passes nearly upon that mentioned by Piazzi, "alia 8æ magnit. praecedit 3" temporis, 3' ad Boream." A, or Sirius, is subject to a large proper motion, the values of which have been stated as follows:

    P....  RA -0".51 Dec. -1".14
    B....     -0".48      -1".23
    A....     -0".53      -1".23
   [Hipparcos -0".54601   -1".22307]

Sirius, the dog-star, and one of Orion's hounds, is the brightest of all the stars in the firmament, and therefore regarded as their chief; for I have frequently compared it with Canopus, the next in brilliance, when both were nearly on the meridian together, and the latter yielded the palm to Kúwv. From this brilliance there is little probability of its being mistaken for any of its stellar neighbours; but it may be noted, that a line from the Pleiades through Orion's belt passes, at about 20° beyond the latter, through Sirius. The geometrical diagram here presented to the gaze, was not lost to the rhymester:

    Let Procyon join with Betelgeuze,         and pass a line afar,
    To reach the point where Sirius glows—    the most conspicuous star;
    Then will the eye delighted view          a figure fine and vast,
    Its span is equilateral,                  triangular its cast.

This star derived its Greek name from Σειριος, in allusion to the brightness, heat, and dryness assigned to it; though Dr. Hutton gravely informs us that the term is from Siris, which he says is the most ancient appellation of the Nile, for when this star rose heliacally, and became visible to the Egyptians and Ethiopians, their year commenced, and with it the inundation of their fecundating river. As that beneficial flood was attributed to the influence of the beautiful star, it was therefore worshipped as Sothis, Osiris, and Latrator Anubis*; and was viewed as the abode of the soul of Isis. Jacob Bryant insists, that the word Sirius was borrowed by the Greeks from the Egyptian Cohen Sehor; and others recognise in it the Mazzarotk of Job; while Novidius, who gave a scriptural meaning to each constellation, says it alludes to Tobit's dog: "and so it may," ejaculates Moxon, "because he hath a tayle." It is first mentioned as a star by Hesiod, though Wyllyam Salysbury, 1550, and Heyschius, contend that the name applies equally to the Sun and the dog-star; and Homer, albeit he does not cite Sirius by name, compares the brightness of Achilles' armour to the pernicious blaze of the dog-star;

                   Whose burning breath
    Taints the red air, with fevers, plagues, and death.

Some of the ancients asserted that a star in the head of the Dog perfectly distinguishable from Sirius, perhaps meaning γ, was designated Isis, in former ages; but they were assuredly in error, as may be inferred from Diodorus and Plutarch, and all the honours of the constellation were vested in the dog-star. Lælaps, one of Actæon's kennel, was, however, slipped in, and moreover the Latins called it Canis Candens, and Canicula; which last should seem to apply to the Lesser Dog, but that, among the many opinions on this serious topic, the shew of hands is for Sirius. Yet Horace, inviting Mæcenas to quit the "Fumum et opes strepitumque" of Rome, (one would think London was meant,) for the country, during hot weather, thus describes the aspect of the heavens :

Jam clarus occultum Andromedæ pater (Cepheus)
Ostendit ignem; jam PROCYON furit,
Et stella vesani Leonis (Regulus),
Sole dies referente siccos.

There is no end to the evil influences which the ancients attributed to this star, though Geminus considered the bulk of them as rather resulting from the Sun; yet he was borne down by those who held Sirius to be an object equally terrible and splendid. While Virgil and others considered the unhealthy and oppressive period, which followed the summer solstice in Italy, was owing to the presence of the dog-star, Manilius thought it was a distant sun to illumine remote bodies; and thus he speaks, through the means of Sherburne:

    'Tis strongly credited this owns a light
    And runs a course not than the Sun's less bright,
    But that remov'd from sight so great a way
    It seems to cast a dun and weaker ray.

From its heliacal rising the ancients reckoned their dies caniculares, or dog-days, which, however, in our climate, often commenced a fortnight after the veritable dog-days were ended; they have been frequently shifted and adjusted, and now seem to be established among the Almanacks, from the 3rd of July to the llth of August; i.e. before Sirius rises! An extraordinary influence in engendering diseases among men, and madness among dogs, was assigned to the canicular days; hence their advent was of paramount importance, and Theon Alexandrinus has left a full formula, to find the exact time of the dog-star's rising; twenty days before which, and twenty days after, included the period of perspiration, hydrophobia, and other evils.

Canis Major is situated in the Southern Hemisphere, below Orion's feet; and the appellation of the principal star was frequently applied to the whole asterism, as an emblem of watchfulness and fidelity; hence its name Alshira, from the Arabic Ash-shi'ra-l-Yemeníyah, the bright shining star of Yemen, or Arabia Felix. This Shi'ra, it will be remembered, is largely complimented by Mahomet, in the fifty-third Sura of the Koran. The Greater Dog is one of the old 48 constellations, and has been thus tabulated :

    Ptolemy  . . . 29 stars  Hevelius . . . .  22 stars
    Tycho Brah . . 13        Flamsteed  . . .  31
    Bayer  . . . . 19        Bode   . . . . . 161

Mr. Barker, of Lyndon, in the fifty-first volume of the Philosophical Transactions, considered that Sirius has changed colour, from red to white, in the lapse of ages; and quotes Aratus, Cicero, Virgil, Ovid, Seneca, Horace, and Ptolemy, in proof. The ancients, however, used the names of colours with the utmost latitude. Splendescere, purpurascere, signified to shine brightly; ποικιλος of Aratus expresses a glittering object; and the rubra Canicula of Horace may allude to heat. Mr. Barker's evidence for the mutation has therein more learning than point; but Seneca has an admission that the redness of Sirius was so strong as to exceed that of Mars; and Ptolemy says it was of the same colour as Cor Scorpii. These witnesses, both men of character and trust, are directly opposed to Hyginus, who asserts that the star was white, flammæ candorum. This Barker gets over, by considering that candor may be used for brightness, without regard to colour; and he might have called in Eratosthenes, a witness of high credit, to prove that Sirius at first signified bright, glittering, sparkling, and was afterwards given exclusively as the name of the most brilliant of the fixed stars. At all events, such a variation would be the more remarkable, since the other principal stars are unchanged in colour. Ptolemy calls Arcturus, Aldebaran, Pollux, Betelgeuze, and Antares, νποκιρρος, or reddish, as they now actually are.

Sirius holds a leading place among the insulated stars, and is considered to be free from disturbance, although it seems to be obvious, that no two stars in the universe can be altogether out of the sphere of each other's attraction: but upon the supposition that the masses of Sirius and our Sun are equal, and that the former has a parallax of 1", it would take about forty millions of years for them to fall to one another by their mutual action.

The brilliance of Sirius has long attracted the attention of philosophers, and every practical astronomer must be conversant with its superiority over its compeers. Sir William Herschel says, that when this star was about to enter his large telescope, the announcing light was equal to that on the approach of sunrise, and upon gaining the field of view, the star appeared in all the splendour of the rising sun, so that it was impossible to behold it without pain to the eye. By Sir John Herschel's photometric experiments on the apparent brightness of stars, the light of Sirius was found to be about 324 times that of an average star of the 6th magnitude. Consequently, if both bodies be assumed as of similar proportions, light diminishing as the square of the distance of the luminous body increases, their respective distances from us must be in the ratio of 57.3 to 1.

Another word upon such astonishing luminosity. My regretted friend Dr. Wollaston, in his skilfully ingenious researches in this branch of photometry, says, "From a comparison which I made in the year 1799 of the light of the Sun with that of the Moon, I should estimate the direct light of the Sun as being nearly one million times greater than that of the Moon; and consequently the direct light of the Sun as very many millions times greater than that afforded us by all the fixed stars taken collectively. Such then being, to our visual organs, the vast dis-proportion in radiance between the Sun and the whole starry firmament, it is not to be expected that we should assign very accurately how much greater the light of the Sun is, than that exceedingly minute quantity of it which shines upon us from any one, even the most brilliant of the fixed stars." We must refer the reader to the 119th volume of the Philosophical Transactions, for the details of his method of obtaining results by approximate ratios, and leap to his conclusion, that "we are not warranted by these experiments in supposing that the light of Sirius exceeds a 20,000,000,000th part of the Sun's light." Dr. W. therefore assuming the low limit of possible parallax of half a second, and consequently its distance from the Earth to be 525,481 times the radius of our orbit, concluded its intrinsic splendour to be nearly equal to that of fourteen suns: and that, if the star were placed where the Sun is, it would appear nearly four times as large as that luminary ! "Well might Voltaire make Micromegas, one of its inhabitants, to be eight leagues in stature.

The wit of Ferney drew his vast ideas of the magnitude of the dog-star from the several computations of modern philosophers. Maginus of Padua, considered the magnitude of Sirius to be equal to 10', Kepler supposed 4', and Tycho thought it was 2'; Ricciolus, however, brought it down to 18": on which assumption its true magnitude was thus tabulated, according to the distance in the Copernican Hypothesis, maintaining the parallax of the fixed stars made by the Earth's motion, not to exceed 10", and imagining the diameter of the annual orbit to be such as upon those principles it is stated to be:

                                          TRUE MAGNITUDE OF SIRIUS.
               Distances in      Diameter of Sirius
AUTHORITIES.   semi-diameter of  contains diameters  The body of Sirius contains
               the Earth.        of the Earth :      the Earth's body :

Copernicus . .     47,439,800           4170             71,677,171,300
Galilæus . . .     49,832,416           4380             88,427,672,000
Bullialdus . .     60,227,920           5300            148,877,000,000
Keplerus . . .    142,746,428          12550          1,967,656,371,000

Exorbitant as this appears, Vendelinus made his distance vastly greater, namely 605 millions of semi-diameters of the Earth. Yet Schickard says, "The speculations that represent the starry heavens the farthest removed from us, and consequently most amplify the stars, are more favourable to truth, for more confined ones would by no means admit of the annual parallax of our globe."

Astronomy is indebted to Sirius upon many counts, but perhaps in none of higher scientific interest, than' that of investigating the knotty question of Parallax. The dazzling splendour of this star, had long created a notion of its being nearer to us than any other of the stellar host, and therefore the fittest for determining the annual parallax of the Orbis Magnus. Huygens, assuming the Sun and Sirius to be of equal magnitude, made some ingenious but rather unsound optical experiments, from whence he concluded the light and diameter of the former to be 27,664 times greater than those of the latter; and that, consequently, the star's distance must be 27,664 times beyond the distance of the Sun from the Earth. From the varieties of the zenith distances observed at Paris, 130 years ago, Cassini II. inferred a parallax in declination amounting to 6" in space, an inference which, though it gave the star still a diameter of 380 millions of leagues, excited the approbation of astronomers; and, from similar variations in the observations of La Caille, at the Cape of Good Hope, a parallax of 4" was deduced. In 1760 Dr. Maskelyne made a proposition to the Royal Society for discovering this desideratum, the finding out of which, would be " the fullest and directest proof of the Copernican System;" the most striking objection to which was, that the enormous displacement of the spectator's place which that system supposed, was not supported by a corresponding change in the positions of the fixed stars. This proposal seems to have had little effect, and the matter slumbered till Piazzi revived it in a confirmation, by the Palermo observations, of La Caille's amount of the parallax of Sirius. This was announced formally to the Italian Society of Sciences; and in the notes to Hora VI. of the Catalogue, Piazzi says, "Juxta meas observationes, qua3 cum iis conveniunt, quas ad Caput Bona? Spei tentavit La Caille, Sirii paralaxis statui probabiliter potest quatuor secundorum circiter*." The question then rested till the recent admirable operations of Messrs. Henderson and Maclear, whose zeal and ability have been so applied as to produce a result, which must ever keep their names on the Fasti of Science. For the observations of these gentlemen, we must direct the reader to the Memoirs of the Royal Astronomical Society, and shall merely give the important result. On resolving, by the method of minimum squares, the two sets of equations, and combining the results according to their relative weights, the greatest effect of parallax in declination is found, from the whole of the 231 observations, = + 0".15; and the greatest effect of aberration in declination, 13".07. These quantities are to the total effect of parallax and aberration in the proportion of 13".13 to 20".50, whence the final results are:

    Parallax of Sirius, (or the angle subtended by the radius of the
    Earth's orbit, at a distance equal to that of the star,) .    . =  0".23
    Constant of Aberration     .    .    .    .    .    .    .    . = 20".41

The possible error of this determination of the parallax may be estimated not to exceed a quarter of a second, as it is almost certain that the constant of aberration is not in error to a greater amount. On the whole, it may be concluded that the parallax of Sirius is not greater than half a second of space, and that it is probably much less. See 61 Cygni. The rigorous investigations by the same astronomers on α Centauri, are equally successful, and are still closely attended to.


* Bainbridge, who was well versed in Arabian astronomy, wrote a treatise, Canicularia, together with a demonstration of the heliacal rising of Sirius for the parallel of Lower Egypt. This was published at Oxford in 1648, five years after his death. The sonorous tetrandryan monogynian bard commemorates the doe-star's advent:

    Sailing in air, when dark monsoon inshrowds
    His tropic mountains in a night of clouds,
    High o'er his head the beams of Sirius glow,
    And dog of Nile, Anubis, barks below.
      *         *         *         *
    Her long canals the sacred waters fill.
    And edge with silver every peopled hill ;
    O'er furrow'd glebes and green savannahs sweep,
    And towns and temples laugh amid the deep.

― A Cycle of Celestial Objects Vol II, The Bedford Catalogue, William Henry Smyth, 1844

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