October 27 & 28. Occultation of op. Immersion Emersion Oct. 27, 11h. 58m. 46s. A. S 0'43" 28, 1 2 39 M. 1 2 November 2. Occultation of y 8. South of the centre. Immersion Emersion 5h. 36m. 50s. M. S 15′ 53′′ 15 10 The importance of occultations of stars by the moon, in the determination of terrestrial longitude, (the latitude being always very easily ascertained,) has long been known. The longitude deduced from the observed immersion or emersion of a star will be as near the truth, as the result of hundreds of lunar distances, or of a large number of transits of the moon and a star; but when the lunar tables are relied on, the longitude, even thus obtained, is liable to some uncertainty, on account of the small error which is sometimes found in them. For the determination of the longitude, those occultations are most suitable, in which the stars disappear or reappear near the centre of the moon, as the time of either of their phenomena taking place is then less affected by an error (should there be any) in her tabular longitude or latitude; particularly in the latter; the longitude, however, deduced from a corresponding observation of the same occultation, made in one of the observatories of Europe, or in any other place, whose geographical position is well determined, will be free not only from error on this account, but from every other but that of observation. Of the seven occultations of Aldebaran which will be visible this year in some parts of the United States, four (those of Jan. 5, May 22, July 16, and Nov. 29,) will likewise be visible in Europe. An opportunity is thus presented, of ascertaining with very great precision the longitude of many of our cities and points on our coast, at present inaccurately known, which may not again occur for several years. On another account, the subject of occultations has at all times been an interesting and important one, both to the practical and theoretical astronomer; viz. that they frequently present some remarkable phenomena with respect to light, when the edge of the moon comes in contact with the star about to be occulted, the star sometimes appearing to be projected on the dise of the moon. This circumstance has lately been very particularly attended to, and numerous instances given by the Astronomical Society of London, who suppose that this appearance is more frequent, (or at least more frequently recorded,) as to Aldebaran, than in the case of any other star, accompanied, however, with anomalies for which it is difficult to account.* It is therefore hoped that our astronomers will be induced to look out for the occultations of this star, not only with a view to ascertain the longitude of the place of observation, but to determine whether it does not appear projected on the face of the moon; in doing this, particular attention should be paid to the following circumstances. *See a paper read before the Astronomical Society of London, by Mr. South, the Vice President, Jan. 1829. 1. Whether the star undergoes any change of light, of colour, or of motion, on its immediate approach to the edge of the moon. 2. Whether it appears to be projected on the moon's disc, and if so for how long a time. 3. Whether the dark limb of the moon be distinctly visible, and well defined, at the time of the phenomenon. 4. Whether the star, on its emersion, appears on the moon's disc, or emerges quite clear of the moon's border. In the occultation of this star, at Boston, August 21 & 22, 1829, the star, at the immersion, did not appear to undergo any change of light, or to be projected on the moon, but was so tremulous, that there was an uncertainty of two seconds in the time of its disappearance; but its emersion was instantaneous. The elements of the eclipses and of the occultations (with the exception of the places of the stars) were computed from the Berlin Astronomisches Jahrbuck for 1830, edited by the celebrated Encke, a work far superior, both as to matter and arrangement, to any thing of the kind hitherto published. Appulses of the Moon to Stars in 1830, calculated for Boston; all or nearly all of which will be Occultations in some part of the United States. D&y 8. star 7' apparently south of D. Feb. 1, 9h. 50m. A. app. April 11, 0h. 12m. M. D & 8 γ north April 19, 5h. 6m. M. south May 27, 7h. 11m. A. July 1, 8h. 40m. A. July 15, 2h. 24m. M. Aug. 12, 1h. 49m. A. Oct. 5, 0h. 29m. M. Long. of Lat. of Long. of D. Lat. of D. H. M. D's Eq. Par. H. Motion. D's Hor. S. D. H. Motion. g-སམྦྷ |: 29 30.6 29 8 42.3 s. 0 +2 24.1 2 54 54 12.3 + 0.2 O's A. R. H. M. 19 6 43.5 19 50 35.0 ཐབ + 21 3 +1 Long. of D. Lat. of D. s. 5 H. M. + 15.5 s. 5° 28' 44.4" s. 5° 44′ 57.6" n. 3° 16′ 54.4" s. 1° 2′ 16.3" 35 4.5 32 41.1 45.33 21.4 Aug. 29, 13h. Sept. 2, 20h. df. + 23.9 +1.1 16 22.0 + 0.6 h. m. s. 10 31 33.6 h. m. 6. 10 47 8.9 |