Fifty-seven navigational stars and additionally the star Polaris are given a special status in the field of celestial navigation. Of the approximately six thousand stars visible to the naked eye under optimal conditions, these selected stars are among the brightest and span thirty-eight constellations of the celestial sphere from the declination of −70° to +89°. Many of the selected stars were named in antiquity by the Babylonians, Greeks, Romans, Arabs and Polynesians.
The star Polaris, often called either the "Pole Star" or the "North Star", is treated specially due to its proximity to the north celestial pole. When navigating in the Northern Hemisphere, a simple and quick technique can be used with Polaris to determine the observers latitude or, for larger maritime vessels can be used to calculate any gyrocompass error that may exist. The other fifty-seven selected stars have daily positions given in nautical almanacs, aiding the navigator in efficiently performing observations on them. A second group of 115 "tabulated stars" can also be used for celestial navigation, but are often less familiar to the navigator and require extra calculations.
Although Polaris can quickly and simply give a solution for latitude in the northern hemisphere, it can not participate in giving a position fix including longitude - it is for this reason it is excluded from the list of 57 primary navigational stars, each of which can be used to produce (in conjunction with each other, known time in relation to the prime meridian and a set of sight reduction tables) an actual latitudinal and longitudinal positional fix.
For purposes of identification, the positions of navigational stars — expressed as declination and sidereal hour angle — are often rounded to the nearest degree. In addition to tables, star charts provide an aid to the navigator in identifying the navigational stars, showing constellations, relative positions, and brightness.
In practical use for sight reductions whilst at sea, tables can further assist a navigator by giving approximate altitudes (angles above the horizon) and azimuths (degrees as read from the compass) from an assumed or estimated position, usually helping to quickly determine the location and then quickly identify a particular navigational star that may be useful for a sight reduction.
Background
Under optimal conditions, approximately six thousand stars are visible to the naked eye of an observer on Earth. Of these, fifty-eight stars are known in the field of navigational astronomy as "selected stars", including nineteen stars of the first magnitude, thirty-eight stars of the second magnitude, and Polaris. The selection of the stars is made by His Majesty's Nautical Almanac Office and the US Naval Observatory, in the production of the yearly Nautical Almanac which the two organizations have published jointly since 1958. Criteria in the choice of stars includes their distribution across the celestial sphere, brightness, and ease of identification. Information for another 115 stars, known as "tabulated stars", is also available to the navigator. This list provides information on the name, approximate position in the celestial sphere, and apparent magnitude of the 58 selected stars in tabular form and by star charts.
These stars are typically used in two ways by the navigator. The first is to obtain a line of position by use of a sextant observation and the techniques of celestial navigation. Multiple lines of position can be intersected to obtain a position known as a celestial fix. The second typical use of the navigational stars is to determine gyrocompass error by computing the azimuth of a star and comparing it to an azimuth measured using the ship's gyrocompass. Numerous other applications also exist.
Navigators typically refer to stars using one of two naming systems for stars: common names and Bayer's designations. All of the selected stars have had a common name since 1953, and many were named in antiquity by the Arabs, Greeks, Romans, and Babylonians. Bayer's naming convention has been in use since 1603, and consists of a Greek letter combined with the possessive form of the star's constellation. Both names are shown for each star in the tables and charts below.
Each star's approximate position on the celestial sphere is given using the equatorial coordinate system. The celestial sphere is an imaginary globe of infinite size with the Earth at its center. Positions on the celestial sphere are often expressed using two coordinates: declination and sidereal hour angle, which are similar to latitude and longitude on the surface of the Earth. To define declination, the Earth's equator is projected out to the celestial sphere to construct the celestial equator, and declination is measured in degrees north or south of this celestial equator. Sidereal hour angle is a measurement between 0° and 360°, indicating how far west a body is from an arbitrarily chosen point on the celestial sphere called the First Point of Aries. Note that right ascension, as used by astronomers, is 360° minus the sidereal hour angle.
The final characteristic provided in the tables and star charts is the star's brightness, expressed in terms of apparent magnitude. Magnitude is a logarithmic scale of brightness, designed so that a body of one magnitude is approximately 2.512 times brighter than a body of the next magnitude.The value is actually the fifth root of 100, an irrational number known as Pogson's Ratio. See Thus, a body of magnitude 1 is 2.5125 (~100) times brighter than a body of magnitude 6. The dimmest stars that can be seen through a 200-inch terrestrial telescope are of the 20th magnitude, and very bright objects like the Sun and a full Moon have magnitudes of −26.7 and −12.6 respectively.
Table Key to the table Column title Description No. The number used to identify stars in navigation publications and star charts.This list uses the assigned numbers from the Nautical Almanac, which includes only 57 stars. Polaris, which is included in the list given in The American Practical Navigator, is listed here without a number. Common name The name of the star commonly used navigation publications and star charts. Bayer designation Another name of the star which combines a Greek letter with the possessive form of its constellation's Latin name. Etymology ofcommon name Etymology of the common name.Bowditch, 2002, p. 248. SHA Sidereal hour angle (SHA), the angular distance west of the vernal equinox. Dec. Declination, the angular distance north or south of the celestial equator. App.magnitude Apparent magnitude, an indicator of the star's brightness. The table of navigational stars provides several types of information. In the first column is the identifying index number, followed by the common name, the Bayer designation, and the etymology of the common name. Then the star's approximate position, suitable for identification purposes, is given in terms of declination and sidereal hour angle, followed by the star's magnitude. The final column presents citations to the sources of the data, The American Practical Navigator and the star's entry at the SIMBAD database, a project of the Strasbourg Astronomical Data Center or CDS.
No. Commonname Bayerdesignation Etymology of common name SHA Declination App.magnitude References 1 Alpheratz α Andromedae the horse's navel 358 N 29° 2.06 2 Ankaa α Phoenicis coined name, "phoenix bird" in Arabic 354 S 42° 2.37 3 Schedar α Cassiopeiae the breast (of Cassiopeia) 350 N 56° 2.25 4 Diphda β Ceti the second frog (Fomalhaut was once the first) 349 S 18° 2.04 5 Achernar α Eridani end of the river (Eridanus) 336 S 57° 0.50 6 Hamal α Arietis full-grown lamb 328 N 23° 2.00 7 Acamar θ Eridani another form of Achernar 316 S 40° 3.2 8 Menkar α Ceti nose (of the whale) 315 N 04° 2.5 9 Mirfak α Persei elbow of the Pleiades 309 N 50° 1.82 10 Aldebaran α Tauri follower (of the Pleiades) 291 N 16° 0.85 var 11 Rigel β Orionis foot (left foot of Orion) 282 S 08° 0.12 12 Capella α Aurigae little she-goat 281 N 46° 0.71 13 Bellatrix γ Orionis female warrior 279 N 06° 1.64 14 Elnath β Tauri one butting with the horns 279 N 29° 1.68 15 Alnilam ε Orionis string of pearls 276 S 01° 1.70 16 Betelgeuse α Orionis the hand of al-Jauzā (i.e. Orion) 271 N 07° 0.58 var 17 Canopus α Carinae city of ancient Egypt 264 S 53° −0.72 18 Sirius α Canis Majoris the scorching one (popularly, the dog star) 259 S 17° −1.47 19 Adhara ε Canis Majoris the virgin(s) 256 S 29° 1.51 20 Procyon α Canis Minoris before the dog (rising before the dog star, Sirius) 245 N 05° 0.34 21 Pollux β Geminorum Zeus' other twin son (Castor, α Gem, is the first twin) 244 N 28° 1.15 22 Avior ε1 Carinae coined name 234 S 59° 2.4 23 Suhail λ Velorum shortened form of Al Suhail, one Arabic name for Canopus 223 S 43° 2.23 24 Miaplacidus β Carinae quiet or still waters 222 S 70° 1.70 25 Alphard α Hydrae solitary star of the serpent 218 S 09° 2.00 26 Regulus α Leonis the prince 208 N 12° 1.35 27 Dubhe α1 Ursae Majoris the bear's back 194 N 62° 1.87 28 Denebola β Leonis tail of the lion 183 N 15° 2.14 29 Gienah γ Corvi right wing of the raven 176 S 17° 2.80 30 Acrux α1 Crucis coined from Bayer name 174 S 63° 1.40 31 Gacrux γ Crucis coined from Bayer name 172 S 57° 1.63 32 Alioth ε Ursae Majoris another form of Capella 167 N 56° 1.76 33 Spica α Virginis the ear of corn 159 S 11° 1.04 34 Alkaid η Ursae Majoris leader of the daughters of the bier 153 N 49° 1.85 35 Hadar β Centauri leg of the centaur 149 S 60° 0.60 36 Menkent θ Centauri shoulder of the centaur 149 S 36° 2.06 37 Arcturus α Boötis the bear's guard 146 N 19° −0.04 var 38 Rigil Kentaurus α1 Centauri foot of the centaur 140 S 61° −0.01 39 Zubenelgenubi α Librae southern claw (of the scorpion) 138 S 16° 3.28 40 Kochab β Ursae Minoris shortened form of "north star" (named when it was that,For more information, see the article changing pole stars. ca. 1500 BC – AD 300). 137 N 74° 2.08 41 Alphecca α Coronae Borealis feeble one (in the crown) 127 N 27° 2.24 42 Antares α Scorpii rival of Mars (in color) 113 S 26° 1.09 43 Atria α Trianguli Australis coined from Bayer name 108 S 69° 1.92 44 Sabik η Ophiuchi second winner or conqueror 103 S 16° 2.43 45 Shaula λ Scorpii cocked-up part of the scorpion's tail 097 S 37° 1.62 46 Rasalhague α Ophiuchi head of the serpent charmer 096 N 13° 2.10 47 Eltanin γ Draconis head of the dragon 091 N 51° 2.23 48 Kaus Australis ε Sagittarii southern part of the bow (of Sagittarius) 084 S 34° 1.80 49 Vega α Lyrae the falling eagle or vulture 081 N 39° 0.03 50 Nunki σ Sagittarii constellation of the holy city (Eridu) 076 S 26° 2.06 51 Altair α Aquilae flying eagle or vulture 063 N 09° 0.77 52 Peacock α Pavonis Coined from the English name of the constellation 054 S 57° 1.91 53 Deneb α Cygni tail of the hen 050 N 45° 1.25 54 Enif ε Pegasi nose of the horse 034 N 10° 2.40 55 Al Na'ir α Gruis bright one (of the southern fish's tail) 028 S 47° 1.74 56 Fomalhaut α Piscis Austrini mouth of the southern fish 016 S 30° 1.16 57 Markab α Pegasi saddle (of Pegasus) 014 N 15° 2.49 * Polaris α Ursae Minoris the pole (star) 319 N 89° 2.01 varThe suffix var after the numeric value denotes a variable star whose magnitude changes over time.
Star charts Key to the Star charts Item Description UPPERCASE TEXTConstellation names are indicated in uppercase text.Selected star of magnitude 1.5 and brighter. Labeled with common name, star number, and Greek letter to indicate Bayer designation.Selected star of magnitude 1.6 and fainter. Labeled with common name, star number, and Greek letter to indicate Bayer designation.Tabulated star of magnitude 2.5 and brighter. Labeled with Greek letter to indicate Bayer designation.Tabulated star of magnitude 2.6 and fainter. Labeled with Greek letter to indicate Bayer designation.Untabulated star. Not labeled.Dotted lineConstellation outline.