CHAPTER 5 – NAUTICAL ASTRONOMY

THE CELESTIAL SPHERE

Celestial sphere. image credits – https://solarsystem.nasa.gov/

It is a sphere with an infinite radius and the center same as the Earth’s center and all heavenly bodies appear to lie on the inner surface of the sphere.

All heavenly bodies appear to rise in the east and set in the west.

Celestial pole – If we extend the axis of the Earth in either direction it will intersect the celestial sphere at the two points called the celestial pole.

Celestial meridians – Semi great circles joining celestial poles are called the celestial meridian.

Celestial equator or Equinoctial – The plane of the equator is extended all around it will intersect the celestial sphere at many points. The locus of the points forms a great circle and is called celestial equator or equinoctial.

Ecliptic – The path of the sun in the celestial sphere is called the ecliptic. The ecliptic is inclined at an angle of 23 and a half with the equinoctial because the Earth’s axis is tilted by the same amount as normal to the plane of the Earth’s orbit.

The ecliptic and equinoctial intersect at two points – FIRST POINT OF ARIES and FIRST POINT OF LIBRA.

HORIZON SYSTEM-

Observer’s Zenith – is the point on the celestial sphere vertically above the observer i.e. the point at which a straight line from the center of the Earth through the observer meets the celestial sphere.

Observer’s Nadir – is the point on the celestial sphere vertically opposite his Zenith.

Vertical circle – The great circle passing through Zenith.

Principal vertical circle (observer’s meridian) – The vertical circle passing through poles is called a principal vertical circle.

Prime vertical circle – It is the vertical circle passing through an east-west point.

Celestial Horizon or Rational Horizon –It is a great circle every point on it is 90 degrees away from Zenith.

Visible Horizon – It is a small circle on the surface of the Earth. Where the sky and the sea appear to meet.

Sensible horizon – It is the plane along with the Horizon sight of the observer parallel to the celestial horizon.

The altitude of the heavenly body– It is the angular distance from the horizon to the heavenly body along the vertical circle passing through the heavenly body.

Azimuth – It is the angle at Zenith between the observer’s meridian and the vertical circle passing through the heavenly body.

With altitude and azimuth of a heavenly body, the heavenly body can be indicated in celestial sphere w.r.t observer.

Zenith distance – It is an angular distance from the zenith to the heavenly body along the vertical circle passing through the heavenly body.

EQUINOCTIAL SYSTEM

Image credits – astronavigationdemystified

Sidereal hour angle (SHA)-

It is an angle at the pole or the angular distance along the equinoctial between the meridian passing through the first point of Aries and meridian passing through the heavenly body measured westward from the meridian through the first point of Aries.

It varies from zero to 360 degrees or 0 hrs. to 24 hrs.

Right Ascension(RA) – It is an angle at the pole or angular distance along the equinoctial between the meridian passing through the first point of Aries and meridian through the heavenly body measured eastwards from the meridian through the first point of Aries.

RA = 360 degree – SHA

Declination – It is the angular distance from the equinoctial till the heavenly body along the meridian measured from zero degree to 90 degrees north or south. If the heavenly body is above equinoctial it has north declination and below equinoctial is south declination.

With SHA and declination, we can indicate the heavenly body in space. This position is fixed in space.

Px = 90 degree – declination

Where Px = polar distance

All about nautical publications

Nautical publications

The nautical publication is a technical term used in maritime circles describing a set of publications, generally published by national governments, for use in safe navigation of ships, boats, and similar vessels. It includes mariner’s handbook which provides information important for the safety of navigation that cannot be represented on charts, and other publications useful to mariners. Nautical publications are intended to be used in conjunction with charts.

OCEAN PASSAGES OF THE WORLD

(BA, NP136) contains the necessary information in preparing the navigation plan for the ocean passage and the Captain may obtain the basic information necessary when deciding the route.

Ocean Passages for the World inc​​​ludes:

  • Individual ch​​​​apters covering each of the world’s oceans, with details of weather, climate, winds, currents, swell, seasonal factors and ice hazards
  • Coverage of the world’s busiest and emerging trade routes to help bridge crew and shore side staff with route planning and the calculation of arrival times
  • Numerous route diagrams and tabulated route data to help users find information quickly, as well as chartlets clearly demonstrating the effects of climate, wave heights and load line zones

SAILING DIRECTIONS

Sailing Direction (Coast Pilot) contains information of weather and sea conditions, the characteristics of the passage and guideline for port entry for all over the world.

All about nautical publications – Sailing direction; Image credits-mdnautical

Sailing direction limits

Sailing direction limits – credits wikipedia

SHIPS ROUTING

Ship’s Routing is published by IMO and contains every information of main passage of the world, traffic separation scheme, deep water routes and area to be avoided.

PURPOSE

The purpose of sea routing is to improve the safety of navigation in concerning areas where the density of traffic is great or where the movement is restricted by sea room.

Content of ship routing

PART A: GENERAL, DESIGN, CRITERIA, AND SYMBOLS

PART B: TSS (TRAFFIC SEPARATION SCHEME)

PART C: DEEPWATER ROUTES

PART D: AREAS TO BE AVOIDED

PART E: OTHER ROUTEING MEASURES

PART F: ASSOCIATED RULES AND RECOMMENDATIONS OF NAVIGATION.

PART G: MANDATORY SHIP ROUTING SYSTEM, ROUTING SYSTEMS

PART H: ADOPTION, DESIGNATION, AND SUBSTITUTION OF ARCHIPELAGIC SERVICES

MARINERS HANDBOOK

All about Nautical publication, image credits amazon.in

The Mariner’s Handbook (NP100) contains clear guidance to help mariners improve their understanding of maritime navigation, sea and ice conditions, meteorology and regulations. A highly valued publication, NP100 is used as a ‘core’ text by many leading maritime training academies and maritime-related organizations.

The Mariner’s Handbook includes:

  • ​​​​Guidance to assist mariners in navigational training and active bridge procedures. Information includes charts and their use, the communication of navigational information, the maritime environment, restrictions to navigation and maritime pollution and conservation.
  • Simple tabular layouts to help users quickly locate essential information, with images to aid the understanding of complex subjects

Also available as an ADMIRALTY e-Nautical Publication

In addition to paper format, the Mariner’s Handbook is available as an ADMIRALTY e-Nautical Publication (AENP). AENPs bring improved efficiency, accuracy, and access to information bridge crews need through electronic NM updates and simple search functionality.

DISTANCE TABLE

Distance Table (NP350) and USA (NVPUB 151) are generally referred all over the world.

This publication helps in finding various distances between ports, Nowadays Second officers rarely use this publication as there are various software to get the same information like port to port and many more. we will suggest you to use that software but also verify information on NP350.

NP350(1) Admiralty Distance Tables Atlantic Ocean Volume 1

NP350(2) Admiralty Distance Tables Indian Ocean Volume 2

NP350(3) Admiralty Distance Tables Pacific Ocean Volume 3

ADMIRALTY LIST OF RADIO SIGNALS

The Admiralty List of Radio Signals consists of the following volumes.

  • Vol.1: Maritime Radio Station NP 281 (Parts 1 & 2).
  • Vol.2: Radio Navigation Aids, Satellite Navigation Systems, Legal Time, Radio Time Signals and Electronic Position Fixing Systems NP 282..
  • Vol.3: Maritime Safety Information Services NP 283 (Parts 1 & 2).
  • Vol.4: Meteorological Observation Stations NP 284.
  • Vol.5: Global Maritime Distress and Safety System (GMDSS) NP 285.
  • Vol.6: Pilot Services, Vessel Traffic Services and Port Operations NP 286 (Parts 1, 2, 3, 4 & 5)

ADMIRALTY LIST OF LIGHT SIGNALS

Admiralty List of Lights consists of 11 volumes (NP74-84) which cover all over the world. The light lists are published by British Admiralty UK.

WEATHER ROUTING CHART

Weather Routing Charts provide expected substantial meteorological information such as waves, currents, wind, Ice, recommended routes, Load Line Zones, etc. There is one chart for each month of the year for the following oceans;

Indian Ocean

North Pacific Ocean

South Pacific Ocean

North Atlantic Ocean

South Atlantic Ocean.

NOTICES TO MARINERS

Notice to Mariners contains corrections to the nautical charts and other publications and are weekly published by the relevant party such as B.A., NIMA, and Maritime Safety Agency in Japan.

Correction of Nautical Publications Navigational warnings and charts and publication and corrections are brought to the Mariners notice by a number of different methods depending on their urgency and importance.

the following methods are available;

a) Annual Notices to Mariners.

b) Weekly Notices to Mariners.

c) Radio Navigational Warnings.