Chapter 19 Sight Reduction
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Celestial Navigation Tutorial
NavSoft’s CELESTIAL NAVIGATION TUTORIAL Contents Using a Sextant Altitude 2 The Concept Celestial Navigation Position Lines 3 Sight Calculations and Obtaining a Position 6 Correcting a Sextant Altitude Calculating the Bearing and Distance ABC and Sight Reduction Tables Obtaining a Position Line Combining Position Lines Corrections 10 Index Error Dip Refraction Temperature and Pressure Corrections to Refraction Semi Diameter Augmentation of the Moon’s Semi-Diameter Parallax Reduction of the Moon’s Horizontal Parallax Examples Nautical Almanac Information 14 GHA & LHA Declination Examples Simplifications and Accuracy Methods for Calculating a Position 17 Plane Sailing Mercator Sailing Celestial Navigation and Spherical Trigonometry 19 The PZX Triangle Spherical Formulae Napier’s Rules The Concept of Using a Sextant Altitude Using the altitude of a celestial body is similar to using the altitude of a lighthouse or similar object of known height, to obtain a distance. One object or body provides a distance but the observer can be anywhere on a circle of that radius away from the object. At least two distances/ circles are necessary for a position. (Three avoids ambiguity.) In practice, only that part of the circle near an assumed position would be drawn. Using a Sextant for Celestial Navigation After a few corrections, a sextant gives the true distance of a body if measured on an imaginary sphere surrounding the earth. Using a Nautical Almanac to find the position of the body, the body’s position could be plotted on an appropriate chart and then a circle of the correct radius drawn around it. In practice the circles are usually thousands of miles in radius therefore distances are calculated and compared with an estimate. -
Chapter 19 the Almanacs
CHAPTER 19 THE ALMANACS PURPOSE OF ALMANACS 1900. Introduction The Air Almanac was originally intended for air navigators, but is used today mostly by a segment of the Celestial navigation requires accurate predictions of the maritime community. In general, the information is similar to geographic positions of the celestial bodies observed. These the Nautical Almanac, but is given to a precision of 1' of arc predictions are available from three almanacs published and 1 second of time, at intervals of 10 minutes (values for annually by the United States Naval Observatory and H. M. the Sun and Aries are given to a precision of 0.1'). This Nautical Almanac Office, Royal Greenwich Observatory. publication is suitable for ordinary navigation at sea, but The Astronomical Almanac precisely tabulates celestial lacks the precision of the Nautical Almanac, and provides data for the exacting requirements found in several scientific GHA and declination for only the 57 commonly used fields. Its precision is far greater than that required by navigation stars. celestial navigation. Even if the Astronomical Almanac is The Multi-Year Interactive Computer Almanac used for celestial navigation, it will not necessarily result in (MICA) is a computerized almanac produced by the U.S. more accurate fixes due to the limitations of other aspects of Naval Observatory. This and other web-based calculators are the celestial navigation process. available from: http://aa.usno.navy.mil. The Navy’s The Nautical Almanac contains the astronomical STELLA program, found aboard all seagoing naval vessels, information specifically needed by marine navigators. contains an interactive almanac as well. -
Chapter 6 Nautical Publications
CHAPTER 6 NAUTICAL PUBLICATIONS INTRODUCTION 600. Publications supply a ship’s chart and publication library. On-line publications produced by the U.S. government are The navigator uses many textual information sources available on the Web. to plan and conduct a voyage. These sources include notices to mariners, summary of corrections, sailing directions, 601. Maintenance and Carriage Requirements of light lists, tide tables, sight reduction tables, and almanacs. Navigation Publications While it is still possible to obtain hard-copy or printed nautical publications, increasingly these texts Vessels may maintain the navigation publications are found online or in other digital formats, including required by Title 33 of the Code of Federal Regulations Compact Disc-Read Only Memory (CD-ROM's) or Parts 161.4, 164.33, and 164.72 and SOLAS Chapter V Digital Versatile Disc (DVD's). Digital publications are Regulation 27 in electronic format provided that they are much less expensive than printed publications to repro- derived from the original source, are currently duce and distribute, and online publications have no corrected/up-to-date, and are readily accessible on the reproduction costs at all for the producer, and only mi- vessel's bridge by the crew. Adequate independent back-up nor costs to the user. Also, one DVD can hold entire arrangements shall be provided in case of libraries of information, making both distribution and electronic/technical failure. Such arrangements include: a on-board storage much easier. The advantages of electronic publications over second computer, CD, or portable mass storage device hard-copy go beyond cost savings. They can be updated readily displayable to the navigation watch, or printed easier and more often, making it possible for mariners paper copies. -
6.- Methods for Latitude and Longitude Measurement
Chapter 6 Copyright © 1997-2004 Henning Umland All Rights Reserved Methods for Latitude and Longitude Measurement Latitude by Polaris The observed altitude of a star being vertically above the geographic north pole would be numerically equal to the latitude of the observer ( Fig. 6-1 ). This is nearly the case with the pole star (Polaris). However, since there is a measurable angular distance between Polaris and the polar axis of the earth (presently ca. 1°), the altitude of Polaris is a function of the local hour angle. The altitude of Polaris is also affected by nutation. To obtain the accurate latitude, several corrections have to be applied: = − ° + + + Lat Ho 1 a0 a1 a2 The corrections a0, a1, and a2 depend on LHA Aries , the observer's estimated latitude, and the number of the month. They are given in the Polaris Tables of the Nautical Almanac [12]. To extract the data, the observer has to know his approximate position and the approximate time. When using a computer almanac instead of the N. A., we can calculate Lat with the following simple procedure. Lat E is our estimated latitude, Dec is the declination of Polaris, and t is the meridian angle of Polaris (calculated from GHA and our estimated longitude). Hc is the computed altitude, Ho is the observed altitude (see chapter 4). = ( ⋅ + ⋅ ⋅ ) Hc arcsin sin Lat E sin Dec cos Lat E cos Dec cos t ∆ H = Ho − Hc Adding the altitude difference, ∆H, to the estimated latitude, we obtain the improved latitude: ≈ + ∆ Lat Lat E H The error of Lat is smaller than 0.1' when Lat E is smaller than 70° and when the error of Lat E is smaller than 2°, provided the exact longitude is known. -
Thenauticalalmanac.Com the Nautical Almanac 2023 for The
The Nautical Almanac 2023 For the Sun TheNauticalAlmanac.com Contents Credits, Acknowledgment and Disclaimer p. 3 Useful Links p. 4 Formulas p. 5 - 7 Equation of Time curve p. 8 The Daily Pages for the Sun p. 9 - 21 Increments & Corrections (The Yellow Pages) p. 22 - 41 Conversion of Arc to Time p. 42 Altitude Corrections for Sun, Planets, Stars (includes Refraction and Dip) p. 43 - 44 USNO Navigational Star Chart p. 45 Sun TOCC.odt Acknowledgment and Credits Dr. Enno Rodegerdts The Nautical Almanac Daily Pages and Sun Almanacs found on our site were originally created from PyAlmanac written by the great Norwegian sailor Enno Rodegerdts. PyAlmanac used PyEphem to generate the almanacs and LaTex provided the final formatting. Visit Dr. Rodegerdts site and learn of his voyages at https://sv-inua.net/ Without his work TheNauticalAlmanac.com wouldn't exist. Andrew Bauer Mr. Bauer has taken the initial work of Dr. Rodegerdts and improved it to the excellence found in the following Daily Pages. Attending foremost to the accuracy of data and then formatting Mr. Bauer created SkyAlmanac which draws from Brandon Rhodes work Ephem and Skyfieldand provides a clear arrangement of figures required for celestial navigation. To that end his work was determined, tireless and efficient. In our mutual writing across many lines of longitude he has always been pleasant, friendly and most affable. As he has said, "The art of celestial navigation should be promoted, not discouraged, even in the modern day". To both of these men we all owe a large debt of gratitude and thanks Disclaimer and Warning Prior to use verify the accuracy of The Nautical Almanac or data you download from our site. -
Chapter 6 Nautical Publications
CHAPTER 6 NAUTICAL PUBLICATIONS INTRODUCTION 600. Publications supply a ship’s chart and publication library. On-line publications produced by the U.S. government are The navigator uses many textual information sources available on the Web. to plan and conduct a voyage. These sources include notices to mariners, summary of corrections, sailing directions, 601. Maintenance and Carriage Requirements of light lists, tide tables, sight reduction tables, and almanacs. Navigation Publications While it is still possible to obtain hard-copy or printed nautical publications, increasingly these texts are found on- Vessels may maintain the navigation publications line or in other digital formats, including Compact Disc- required by Title 33 of the Code of Federal Regulations Read Only Memory (CD-ROM's) or Digital Versatile Disc Parts 161.4, 164.33, and 164.72 and SOLAS Chapter V (DVD's). Digital publications are much less expensive than Regulation 27 in electronic format provided that they are printed publications to reproduce and distribute, and online derived from the original source, are currently publications have no reproduction costs at all for the pro- corrected/up-to-date, and are readily accessible on the ducer, and only minor costs to the user. Also, one DVD can vessel's bridge by the crew. Adequate independent back-up hold entire libraries of information, making both distribu- arrangements shall be provided in case of tion and on-board storage much easier. electronic/technical failure. Such arrangements include: a The advantages of electronic publications over hard- copy go beyond cost savings. They can be updated easier second computer, CD, or portable mass storage device and more often, making it possible for mariners to have fre- readily displayable to the navigation watch, or printed quent or even continuous access to a maintained paper copies. -
Celestial Navigation Practical Theory and Application of Principles
Celestial Navigation Practical Theory and Application of Principles By Ron Davidson 1 Contents Preface .................................................................................................................................................................................. 3 The Essence of Celestial Navigation ...................................................................................................................................... 4 Altitudes and Co-Altitudes .................................................................................................................................................... 6 The Concepts at Work ........................................................................................................................................................ 12 A Bit of History .................................................................................................................................................................... 12 The Mariner’s Angle ........................................................................................................................................................ 13 The Equal-Altitude Line of Position (Circle of Position) ................................................................................................... 14 Using the Nautical Almanac ............................................................................................................................................ 15 The Limitations of Mechanical Methods ........................................................................................................................ -
Concise Sight Reductin Tables From
11-36 Starpath Celestial Navigation Course Special Topics IN DEPTH... 11-37 11.11 Sight Reduction with the NAO Tables money and complexity in the long run by not having to bother with various sources of tables. With this in Starting in 1989, there was a significant change in the Location on table pages N S Declination mind, we have developed a work form that makes the Top Sides available tables for celestial navigation. As we have same + D° D' use of these tables considerably easier than just following sign B = sign Z learned so far, the tables required are an almanac Latitude N S LHA contrary - 1 and a set of sight reduction tables. In the past sight the instructions given in the almanac. With the use + if LHA = 0 to 90 SR Table A° A' + B° B' + Z1 - if LHA = 91 to 269 of our workform, the NAO tables do not take much 1 ------------------> - - reduction (SR) tables were usually chosen from Pub + if LHA = 270 to 360 249 (most popular with yachtsmen) and Pub 229 longer than Pub 249 does for this step of the work. F° F' Naturally, the first few times go slowly, but after a few which is required on USCG license exams. The latter bar top means rounded examples it becomes automatic and easy. The form value 30' or 0.5° rounds up have more precision, but this extra precision would guides you through the steps. + if F = 0 to 90 rarely affect the final accuracy of a celestial fix. Pub A F SR Table H° H' P° P' + Z2 2 ------------------> - - if F = 90 to 180 229 is much heavier, more expensive, and slightly We have included here a few of the earlier examples, more difficult to use. -
Hydrographic Note
HYDROGRAPHIC NOTE (For instructions, see next page) Toitu- Te Whenua Land Information New Zealand New Zealand Hydrographic Authority Level 7, Radio New Zealand House 155 The Terrace PO Box 5501 Wellington 6145 New Zealand Phone: 0800 665 463 or +64 4 460 0110 Email: [email protected] Date ......................................................................... Ref.No. .................................................................................. Name and address of ship or sender ................................................................................................................................................................................ ................................................................................................................................................................................ Tel/Email of sender ................................................................................................................................................. General locality ...................................................................................................................................................... Subject ................................................................................................................................................................... Position Lat.........................................................................Long............................................................................ Position fxing system used ................................................................................................................................... -
The Motion of the Observer in Celestial Navigation
The Motion of the Observer in Celestial Navigation George H. Kaplan U.S. Naval Observatory Abstract Conventional approaches to celestial navigation are based on the geometry of a sta- tionary observer. Any motion of the observer during the time observations are taken must be compensated for before a fix can be determined. Several methods have been developed that ac- count for the observer's motion and allow a fix to be determined. These methods are summarized and reviewed. Key Words celestial navigation, celestial fix, motion of observer Introduction The object of celestial navigation is the determination of the latitude and longitude of a vessel at a specific time, through the use of observations of the altitudes of celestial bodies. Each observation defines a circle of position on the surface of the Earth, and the small segment of the circle that passes near the observer's estimated position is represented as a line of position (LOP). A position fix is located at the intersection of two or more LOPs. This construction works for a fixed observer or simultaneous observations. However, if the observer is moving, the LOPs from two consecutive observations do not necessarily intersect at a point corresponding to the observer's position at any time; if three or more observations are involved, there may be no common intersection. Since celestial navigation normally involves a single observer on a moving ship, something has to be done to account for the change in the observer's position during the time required to take a series of observations. This report reviews the methods used to deal with the observer's motion. -
Intro to Celestial Navigation
Introduction to Celestial Navigation Capt. Alison Osinski 2 Introduction to Celestial Navigation Wow, I lost my charts, and the GPS has quit working. Even I don’t know where I am. Was is celestial navigation? Navigation at sea based on the observation of the apparent position of celestial bodies to determine your position on earth. What you Need to use Celestial Navigation (Altitude Intercept Method of Sight Reduction) 1. A sextant is used to measure the altitude of a celestial object, by taking “sights” or angular measurements between the celestial body (sun, moon, stars, planets) and the visible horizon to find your position (latitude and longitude) on earth. Examples: Astra IIIB $699 Tamaya SPICA $1,899 Davis Master Mark 25 $239 3 Price range: Under $200 - $1,900 Metal sextants are more accurate, heavier, need fewer adjustments, and are more expensive than plastic sextants, but plastic sextants are good enough if you’re just going to use them occasionally, or stow them in your life raft or ditch bag. Spend the extra money on purchasing a sextant with a whole horizon rather than split image mirror. Traditional sextants had a split image mirror which divided the image in two. One side was silvered to give a reflected view of the celestial body. The other side of the mirror was clear to give a view of the horizon. The advantage of a split image mirror is that the image may be slightly brighter because more light is reflected through the telescope. This is an advantage if you are going to take most of your shots of stars at twilight. -
Navigational Algorithms
NNAAVVIIGGAATTIIOONNAALL AALLGGOORRIITTHHMMSS SSiigghhtt RReedduuccttiioonn wwiitthh MMaattrriicceess © Andrés Ruiz San Sebastián – Donostia 43º 19’N 002ºW http://www.geocities.com/andresruizgonzalez 2 Índice Finding position by stars .............................................................................................................. 3 Two Observations........................................................................................................................ 3 Iteration for the assumed position ............................................................................................ 3 3 Observations............................................................................................................................. 4 n Observations............................................................................................................................. 4 Appendix A1. Algorithms ............................................................................................................................. 5 A2. Examples............................................................................................................................... 8 3 Observations ......................................................................................................................... 8 A3. Software .............................................................................................................................. 11 A4. Source code .......................................................................................................................