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PRELIMINARY OBSERVATIONS ON THE ASTRONOMI

CAL DEPARTMENT.

THE year 1833 is less distinguished than either of the two preceding years, for phenomena worthy the attention of our astronomers, since in the course of it, neither the Sun, nor any planet or principal star, will be eclipsed, in the United States; but the three eclipses of the Moon will undoubtedly be viewed with interest by the public generally, since the whole of that which happens on the morning of the 6th of January will be visible to us, and a large part of those which take place in the evening of the 1st of July, and the 26th of December. In the last case, the Moon will, when rising, be seen totally immersed in the shadow of the Earth throughout a very large portion of the country.

The importance of occultations of the fixed stars for the determination of terrestrial longitude is well known; a computation of those for Charleston and Boston, as to stars that are not of less than the sixth magnitude, will be found in the Almanac, by the assistance of which the time of Im mersion or Emersion at any other place not very remote, may be determined with sufficient precision to prepare for observation. Occultations of stars of less than the sixth magnitude have not been computed, on account of the exceeding difficulty of observing them satisfactorily with any other than the largest and most powerful telescopes; those conjunctions of the Moon, however, with these stars, which may prove to be occultations in this country, are marked in the Calendar pages with an asterisk, instead of the usual symbol of conjunction.

The catalogue of the Eclipses of Jupiter's satellites contains those only which may be visible in some part of the United States. The eclipses before the planet comes into conjunction with the Sun (on the 1st of April), will happen on the east side; then, until the opposition (on the 23d of October), on the west; and afterwards again on the east: between the 1st of April and 23d of October, the Immersions only, of the first and second satellites, will be visible, and during the remainder of the year, the Emersions only; but both the Immersion and Emersion in the case of the two other satellites can sometimes be seen.

The eclipses take place farthest from the body of Jupiter when in quadrature, and nearest when in opposition or conjunction; but for some weeks before and after he is in either of the latter positions the eclipses cannot be observed, the planet and satellites being rendered invisible by the superior light of the Sun. As these eclipses appear to take place at the same moment of absolute time in every part of the Earth where they are visible, to determine the time, at which any one in the catalogue will happen in any place in the United States, it is necessary merely to subtract the estimated longitude of that place from the time of immersion or Emersion at Greenwich.

Those who are in possession of a good telescope will doubtless notice with attention the appearance of Saturn between the 30th of April and 10th a*

of June, during which interval his rings will be invisible; the cause of their disappearance at that time is mentioned in a note at the bottom of the 15th page.

In the table of Latitude and Longitude of some of the principal places in the United States (page 21, &c.), will be found the latitude of several, as determined by the editor, by recent observations made by himself; also the longitude of a few, deduced by him from observations made by others, on the annular eclipse, of February 1831, or as ascertained by comparison of the place in question, by chronometers, with the Capitol at Washington, the University of Virginia, Philadelphia, or Boston, the distance of which from the meridian of Greenwich is supposed to be correctly known. The longitude of the Capitol is the mean of the results, deduced from the observations on the annular eclipses of 1791, 1811, and 1831, and has recently been confirmed by the editor, by comparing it by chronometers with the University of Virginia and the city of Philadelphia. The unfortunate adoption, in the construction of several maps of this country, of the longitude of the Capitol (5h. 7′ 42′′), reported by an individual acting under authority of a Resolve of Congress, has caused an error of 63 minutes of a degree therein. Since this table went to press, the position of several places in Maine, New Hampshire, Massachusetts, and Rhode Island, has been determined by the editor, the publication of which must be deferred until another year.

In the arrangement of the Calendar pages there is but little alteration from that in the Almanac for 1832.

The beginning and end of twilight, and the rising and setting of the Sun and Moon, are given for five places in the United States, situated in different latitudes; the Almanac is thus adapted to the inhabitants of every part of the country, as these particulars depend simply on the latitude, and are wholly independent of the longitude.

The column headed Boston, &c. will answer for all places north of latitude 41° 32', that is, British Continental North America, Maine, New Hampshire, Vermont, Massachusetts, and Michigan; all but the southern extremity of New York and Rhode Island; the northern half of Connecticut, the northern third of Pennsylvania, the Connecticut Reserve in Ohio, and the northern extremities of Illinois and Indiana.

The column headed New York, &c. is intended for places situated between latitude 41° 32′ and 39° 48′, that is, the southern extremities of New York and Rhode Island, all but the northern third of Pennsylvania, all but the southern extremity of New Jersey, the central parts of Ohio, Illinois, and Indiana, and the northern third of Missouri.

The column headed Washington, &c. may be used between latitude 39° 48′ and 35° 52', that is, throughout Maryland, Virginia, Delaware, the District of Columbia, and Kentucky, the northern half of Tennessee, the southern extremity of New Jersey, the southern third of Ohio and Indiana, the southern half of Illinois, all but the northern third of Missouri, and the northern third of North Carolina and Arkansas.

The column headed Charleston, &c. is suited to places between latitude 35° 52′ and 31° 24′, that is, South Carolina, all but the southern extremities of Georgia, Alabama, and Mississippi, all but the northern third of North Carolina and Arkansas; the southern half of Tennessee; the northern half of Louisiana.

The column headed New Orleans, &c. is adapted to places south of latitude 31° 24', that is, all Florida and Texas, the southern half of Louisiana, and the southern extremities of Georgia, Alabama, and Mississippi.

The setting of the Moon is given from new moon to full, and the rising from full moon to new; the letters M. A. m. a., to be found in these columns and in other parts of the Almanac, are used to denote Morning and Afternoon.

The time of the Phases of the Moon is computed for the meridian of Washington, but may be readily reduced to that for any other meridian, by adding or subtracting the difference of the longitude, according as the same is east or west of that city. The time of the moon's southing is computed for the same meridian. The variation, however, even in a remote part of the United States, will be inconsiderable.

The time of High Water is corrected for the difference of the Right Ascension of the Sun and Moon, and the distance of the Moon from the Earth. The small corrections depending on their declinations and our distance from the Sun, have been neglected as unimportant; indeed it has been ascertained, from a series of several hundred observations, that the corrections we have introduced will, in calm weather, give the time of high water within fifteen minutes, and, generally, much nearer. The difference between the time of high water at New York, Charleston, and Boston, was derived from the best authorities; but perhaps it has not been ascertained with the degree of accuracy that is to be desired. If our authorities are correct, the time of high water along the coast of Maine, New Hampshire, and Massachusetts, as far as Nantucket, is nearly the same as at Boston. Moreover, when it is high water in New York, it is nearly so in Long Island Sound, along the coast of New Jersey, Delaware, Maryland, Virginia, and North Carolina, as far as Cape Lookout (with the exception of Sandy Hook and the entrance of Chesapeake Bay); whilst in Buzzard's Bay and Narraganset Bay, along the coast of the southern part of North Carolina, of South Carolina, Georgia, and Florida, at Sandy Hook, and the entrance of the Chesapeake, the time agrees very nearly with that in the column for Charleston; when greater accuracy is desired, reference should be had to the Tide Table on the 20th page. The time of the tide immediately preceding the southing of the moon, only, having been given, it should be corrected by the addition of half the difference when the time of the other tide is required.

The Planets are placed in the order in which they pass the meridian on the first day of each month, and their declinations are computed for the moment of their passage over the meridian of Washington.

The Ephemeris of the Sun is taken from the celebrated Almanac of Professor Encke. It contains the Sun's Semidiameter, the time (mean) occupied by the Semidiameter in passing the meridian, his declination, the mean time at the instant his centre is on the meridian of Berlin, the Sidereal time, and the obliquity of the ecliptic. The epoch of the Sidereal time is noon mean time, and that of the declination and of the equation is noon apparent time, of the meridian of Berlin, which is Oh. 53' 35.4" east of Greenwich.

The quantity in the column of the mean time at apparent noon at Berlin is constantly to be added to apparent time to reduce it to mean; indeed, with the exception of the epoch of the equation and declination of the Sun, mean time has been altogether used in the Almanac for 1833.

The apparent places of twenty-five stars, as determined by Professor Bessel at Königsberg, will be found very useful for ascertaining the time or the latitude. The Declination in some instances will be found to differ from that given in the English Nautical Almanac, more than was to be expected in the present improved state of astronomical instruments. This difference sometimes amounts to four seconds; a quantity too great to be altogether ascribed to the use of different tables of refraction.

The table of Refractions is that computed on principles explained by the late Dr. Thomas Young, and is recommended by its great simplicity; moreover, it is said to agree as closely as any other with the latest observations; nevertheless had not Professor Bessel's new table required the use of logarithms, it would have been preferred.

In the year 1834 will happen several very important astronomical phenomena in the United States, the most interesting of which will be the eclipse of the Sun, in the afternoon of Sunday, November 30th; which will be very large throughout the whole country, and total in some part of the States of South Carolina and Georgia.

Boston, October 4, 1832.

R. T. P.

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