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DEFINITION OF ASTRONOMICAL TERMS. Aberration.-An apparent change of place in the fixed stars, which arises from the motion of the earth combined with the motion of light.
Altitudes.—The Altitude of an object is that portion of a vertical circle which is intercepted between the centre of the celestial object and the horizon.
Aphelion.—That point in the orbit of a planet in which it is at its greatest distance from the sun.
Apogel.—That point in the orbit of the moon or a planet in which it is at its greatest distance from the earth.
Azimuths.—The Azimuth of an object is its true bearing, east or west, of its nearest meridian. It is always equal to that portion of the horizon which is intercepted between the vertical circle passing through the centre of the object and the meridian of the place of observation.
Declination of a Celestial Object.— The Declination of any celestial object is its distance north or south from the equinoctial, and is measured by that portion of the celestial meridian which is intercepted between the centre of the object and the equinoctial.
Disk of the Sun or Moon is its round face, which, on account of the great distance of the object, appears flat as like a plane surface.
Diurnal.—Diurnal motions of the planets are the spaces they move through in a day.
Elongation. The angular distance of a planet from the sun as it appears to us upon the earth.
Emersion. The time when any planet which is eclipsed begins to recover its light again.
The Horizon.—The visible horizon is that which is seen while the eye is elevated above the surface; and the sensible is that which is seen when the eye is on a level with the water. The depression of the former below the latter is called the dip of the visible horizon.
Immersion.—The moment when an eclipse begins, or when a planet enters into a dark shadow.
Libration. -An apparent irregularity of the moon's motion, which makes her appear to librate about her axis in such a manner that parts of her eastern and western limbs become visible and invisible alternately:
Parallax.- Parallax is the difference between an altitude taken at the surface of the earth, and that taken at the centre at the same time. When the object is on the horizon, it is called the horizontal parallax ; but in any other case it is called the parallax in altitude.
Penumbra.—A faint shadow which accompanies an eclipse and occasions a partial obscurity of the body to that part of the earth on which it falls.
Perigee.—That point of the moon or a planet's orbit in which it is at its least distance from the earth.
Perihelion.—That point of a planet's orbit in which it is at its least distance from the sun.
Phases. The several appearances of the moon and planets, according as a greater or less part of their illuminated hemishperes are presented to our sight.
Prime Vertical Circle.-The Prime Vertical Circle is the circle which passes from the zenith due east or west, having 90 degrees of the horizon intercepted between it and the meridian, All objects on this circle are said to be on the prime vertical.
Polar Distance of any celestial object, is an arc of a meridian, contained between the centre of that object and the pole of the equinoctial; or, in other words, it is the distance of the object from the elevated pole.
Refraction.-Refraction is a quantity by which a body appears above its true place in the heavens.
Right Ascension.—The Right Ascension of a celestial body is that portion of the equinoctial which is intercepted by a celestial meridian passing through the centre of the body and the first point of the ecliptic. It is generally given in time.
Right Ascension of the Meridian.— The Right Ascenson of the Meridian is that part of the equinoctial that comes to the Meridian with the object measured from the first point of Aries.
Terrestrial and Celestial Equators.-The Terrestrial Equator is a great circle (supposed to be described) around the earth, at an equal distance, or 90 degrees from the poles, dividing the globe into two equal parts; the part to the southward of the equator being called the southern hemisphere, and that to the northward the northern hemisphere.
The Celestial Equator, commonly called the Equinoctial, is an imaginary circle described in the heavens, corresponding to and coinciding with the terrestrial equator.
Time.—Time is measured by the apparent motion of a celestial body over the surface of the globe, and is called Solar, Lunar, or Sidereal, according to the body with which it is referred ; a full revolution of either of these objects is called its apparent day, and begins when the object comes to the meridian; but for the convenience of civil and commercial business, that of the sun, called solar or civil time, is from midnight to midnight, the first twelve hours of which are marked A. M., signifying ante meridian, and the last tweve hours P. M., signifying post meridian. In this and the following mode of keeping time, the day is dated as soon as it commences.
Astronomical Day.-This day is also measured by the apparent motion of the sun, but for the convenience of astronomical computations, it is taken to begin at noon, that is, 12 hours after the beginning of the civil day, and end at noon of the following day. Astronomers generally reckon the hours of this day up to 24 hours, without any distinction of ante or post meridian, which they call astronomical time; hence the first 12 hours of which are the P. M. hours of the civil day on which it begins, and the last 12 hours of it are the A. M. hours of the day on which it ends.
The Nautical Day.—This day, as well as the civil and astronomical day, is measured by the apparent motion of the sun. It begins just with the astronomical day, but it is dated with the noon on which it ends; hence it is 24 hours in date later than the astronomical day, the first 12 hours of which are marked in the journal with P. M., and the last 12 hours with A. M., so that occurrences which happen on the afternoon of the civil day on which it begins, come in the journal under the date of the civil day in which it ends. The Log Book is generally kept in nautical or Sea Time, but it may be kept in Common or Civil Time.
Tropics.- The Tropics are two circles (supposed to be described) parallel to the equator, at the distance of about 23° 28', equal to the highest declination. The northernmost is called the Tropicor Cancer, and the other the Tropic of Capricorn.
Twilight.—The Twilight is that duration of light which is apparent in the absence of the sun. It generally continues whilst he is traversing about 18 degrees below the horizon. It is caused by the column of atmosphere which surrounds the earth receiving the rays, or light, of the sun, and from which that light is transmitted to those parts of the surface of the globe opposite the sun at its rising and setting.
Vertical Circles.- Vertical Circles are circles (supposed to be described in the heavens) perpendicular to the horizon, and meeting at the Zenith. They are sometimes called circles of altitudes, circles of azimuths, and prime vertical circles.
Zenith and Nadir.-The Zenith is that point in the heavens which is directly over the observer's head; and the Nadir that which is opposite to it.
Zenith Distance.-The Zenith Distance of a celestial object is equal to that portion of the vertical circle which is intercepted between the centre of the object and the observer's zenith. It is always equal to the complement of the altitude to a quadrant, or 90 degrees.
EXPLANATION OF COMPASS TERMS. Variation of the Compass is the angle between the True North and the Magnetic North. This difference or error arises from the Magnetic Poles not coinciding with the Terrestrial ones, and is due entirely to the influence of the earth on Magnetic Needles, which is the same at few parts of the world.
Deviation of the Compass is the angle included between the Magnetic North and the Compass North, This error is due to the disturbing influences of the iron of which the ship is built, as rudderposts, masts, chains, funnel, &c. ; her position when building, her cargo, or other causes within the ship.
Local Attraction is the error caused by some distarbing force outside the ship, and belonging entirely to the locality at which a ship may be-as mooring posts or chains, dock cranes, another iron vessel alongside, volcanic or magnetic influences, &c.
Heeling Error is the effect produced on the Compass by the heeling of an iron or composite ship, the angle increasing with the amount of Heel.
Leeway is the angle between the ship's course by Compass and the direction which she makes through the water, as shown by her wake.
Compass Course is the course steered by ship's Compass.
Magnetic Course is the Compass Course corrected for Deviation and Leeway.
The True Course of a Ship is the Compass Course corrected for Deviation, Leeway, and Variation.
EXPLANATION OF ASTRONOMICAL CHARACTERS. O The Sun.
? Ceres. ( The Moon.
# Juno. ☆ Mercury.
4 Jupiter. 8 Venus.
h Saturn. The Earth.
8 Descending Node.
SIGNS OF THE ZODIAC, &c. o Aries (the Ram), oo
* Sextile, when two signs diso Taurus (the Bull), 30°
tant, or differing 60° in Gemini (the Twins), 60°
Longitude or Rt. Ascension. Cancer (the Crab), 90° o Quartile, when three signs 12 Leo (the Lion), 120°
distant, or differing 90° in me Virgo (the Virgin), 150°
Longitude or Rt. Ascension. - Libra (the Balance), 180° 8 Opposition, when six signs m Scorpio (the Scorpion), 210° distant, or differing 180° in f Sagittarius (the Archer), 240° Longitude or Rt. Ascension. v Capricornus (the Goat), 270° e Aquarius (the Waterbearer), * Pisces (the Fishes), 330° (300 N. North. Mins. of Arc.
Secs. of Arc. ó Conjunction, in the same de- E. East. h. Hours.
gree or sign, or having the W. West. m. Mins. of Time
same Longitude or Rt. Ascn. Degrees. Secs. of Time. TERMS AND ABBREVIATIONS USED IN SHIPPING. A/c.--Account. E.E.-Errors excepted. E & 0.E. -Errors and omissions excepted. F.O.B.-Free on board. F.P.A.-Free of particular average. Inst.—Instant, present month. C/I/F.--Cost, Insurance & Freight. Prox.- Proximo, next month. Ult.-Ultimo, last month. D/D.-Days after Date. M/D.-Months after date. D/S.-Days after sight. %-Per cent. @-At, to. P-Per. B/L.— Bill of Lading. Ad valorem.-According to value. Adjustment.--The settlement of a loss incurred by the insured. Adventure.-Goods consigned to a party to be made the most of. Agio.- The Premium borne by a better sort of money above an inferior. Appraise.—To value goods imported. Assets-A term for property and money in contradistinction to liabilities. Assurance. -See Insurance. Average. -A sacrifice made to prevent the total loss of a ship or
cargo ; an average of the loss insured for the benefit of
all concerned, to be made good proportionately. Award. --The decision in arbitration. Banco.-A continental term for bank money at Hamburg and other
places. Barratry. - A fraudulent act on the part of the master or crew of a
vessel, against the interest of the owners. Insurances
are effected against barratry. Bill of Health. -A certificate granted by Consuls and Customs
Officers as to health of port. Bill of Lading.- A master's acknowledgment and undertaking as
to receipt and delivery of goods or cargo. Bottomry.-Money borrowed on a ship's bottom or hull, to be
repaid with interest if the ship return in safety, but if not to be lost or forfeited. Sometimes it is raised on the
lading and master's personal security ; see Respondentia. Brokerage. The commission charged by merchants and brokers for
securing and transacting business for ships. Charter Party, -A contract with the owner, agent, or master for
the service of his vessel, Consul.- The commercial representative of one country residing
officially in another,
Credit, Letter of.- A letter written by one party to another,
requesting the party addressed to advance the bearer or
person named a certain sum of money. Days of Grace. - Days allowed by law or custom for payment of
Bills of Exchange (except those payable at sight or on demand) after specified day of payment ; thus, when three days are allowed, as usual in England, a bill due on the
5th of the month is payable on the 8th. Dead Freight.-The damage payable by one who engages to load
a ship fully, and fails so to do. Debenture.-An instrument of the nature of a bill or bond, by
which a debt is claimable. May bear interest or conser some peculiar advantage. It is given at the Custom
House to claim a drawback. Derelict.-Goods cast away or relinquished by wreck or otherwise.
Reductions in duty are also made proportionate to the
damage on them. Deviation is a divergence from the voyage insured which may
release the underwriter from his risk. Drawback.--An allowance granted by Government to encourage
exportation of an article, or a return of duties paid upon
certain articles on exportation. Discount. - An allowance made for money paid before it is due.
To discount a Bill is to buy from the holder the right
to receive the money upon it when due. Dunnage. -Articles used in stowing a cargo or trimming a ship. Embargo.--An order issued by Government to prevent vessels sailing. Flotsam.-Goods floating after a wreck. Jetsam are those sunk.
Lagan are those sunk but secured by a buoy. Groundage.-Money paid in some parts for permission to anchor. Insurance. A contract whereby, for a stipulated consideration,
called a premium, one party undertakes to indemnify the
other against certain risks. Invoice.-A document enumerating goods sold from A to B.
Where the goods are exported by A to be sold on his own account, the document is a specification, and not,
strictly speaking, an invoice. Lay Days.-Days allowed by charter for loading or unloading ships. Lighterage.-The expense of a lighter or barge. Manifest.--The specification of a cargo made out and signed by
the master of a ship. Policy.-A document containing the contract of insurance. A Valued
Policy is when the interest insured is valued. An Open Policy is one in which the amount is left for subsequent proof. In an open policy, where the value shipped does not equal the value insured, the difference is termed over insurance ; and the proportionate amount of premium re
turnable to the insurer is called a return for short interest. Frimage.--A small allowance for the shipmaster's care of goods
now generally included in the freight. Pro rata.- Payment in proportion to the interests concerned. Quid pro quo. -Giving one thing for another. Respondentia.-A contract of loan by which goods in a ship are
hypothecated to the lender, as in bottomry. Super Cargo. -A person sent with a vessel to dispose of its cargo
to the best advantage.