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VISION TECHNOLOGIES : Virtual Celestial Environment for Celestial Navigation


Escola Superior Nautica Infante D. Henrique (ENIDH)

Description of the technological challenge

1. Context, definition of the problem.

The STCW (Standards of Training, Certification and Watchkeeping) Convention requires that training and assessment of seafarers are administered, supervised and monitored in accordance with the provisions of the STCW Code. Knowledge of Celestial Navigation is part of STCW Code including the “Ability to use celestial bodies to determine the ship´s position”.

Astronavigation is the only alternative method to electronic means to determine the ship’s position in ocean navigation. It is used as a secondary method for confirming the position obtained by electronic navigation equipment and, in lack of these, it will be the primary and the only method to get the ship’s position. In this sense, it becomes essential to familiarize the students and simplify the teaching and learning processes of this method.

The training in astronavigation can be summarized in the following items:

- Correctly adjust sextant for adjustable errors;
- Determine corrected reading of the sextant altitude of celestial bodies;
- Accurate sight reduction computation, using a preferred method;
- Calculate the time of meridian altitude of the sun;
- Calculate latitude by Polaris or by meridian altitude of the sun;
- Accurate plotting of position line(s) and position fixing;
- Determine time of visible rising/setting sun by a preferred method;
- Identify and select the most suitable celestial bodies in the twilight period;
- Determine compass error by azimuth or by amplitude, using a preferred method;
- Training in celestial navigation may include the use of electronic nautical almanac and celestial navigation calculation software.

In the training process, students have difficulty in visualizing the celestial sphere, identifying the Sun, Stars, Planets and Moon, used in Astronavigation, and their localization using the Horizontal and Equatorial coordinate systems, the position triangle and apparent movement over the horizon.

The proposed solution will make possible to develop, with greater ease understanding, the acquisition of knowledge for the use of the Astronavigation by the students and by ship’s deck officers at sea.

2.Challenge definition. Description of need.

We propose the development of a solution of vision technologies (immersive 3D environment) that can show the celestial bodies above the horizon with the essential detailed information to train the celestial navigation. This solution will allow to observe the 57 stars and their constellations, the 4 planets, the Sun, the Moon and to show Aries, on the celestial sphere, with the observer located on the deck of a ship.

Other objective of the solution, is allow the user to identify and to understand the apparent movement of celestial bodies

The main objective of the solution is to support students and deck officers to identify and view the main topic of Astronavigation. Depending on the geographic coordinates and time, it will be possible to identify the visible horizon and all the stars that are above the horizon. When selecting the star, the observer should graphically visualize the Horizontal and Equatorial coordinates.

The celestial sphere is an imaginary sphere of infinite radius with the Earth at its centre (Figure above). The north and south celestial poles of this sphere, PN and PS respectively, are located by extension of the Earth's mean pole of rotation. The celestial equator is the projection of the plane of the Earth’s equator to the celestial sphere. A celestial meridian is a great circle passing through the celestial poles and the zenith of any location on the Earth.

The point on the celestial sphere vertically overhead of an observer is the zenith, and the point on the opposite side of the sphere vertically below him or her is the nadir.

The Navigational Triangle is a triangle formed by arcs of great circles of a sphere is called a spherical triangle. A spherical triangle on the celestial sphere is called a celestial triangle.

The spherical triangle of particular significance to navigators is called the navigational triangle, formed by arcs of a celestial meridian, an hour circle, and a vertical circle. Its vertices are the elevated pole, the zenith, and a point on the celestial sphere

The observer should also be able to visualize the position triangle and the values of all coordinates.

Will be desirable, to see the apparent movement in real time or fast motion mode, to identify Sunrise, Sunset and meridian passage.

The solution will be very useful in training, but also in use on ships.

3. Requirements

The type of solution to be proposed must be within the scope of vision technology and must fulfil the following technical requirements, with the main build a virtual sky to Celestial Navigation:

- Possibility of introducing the geographic coordinates of any location for the visualization and time required.
- Automatic update of the coordinates of the Nautical Almanac for each year;
- Possibility to select each type of celestial coordinates, in order to view only partial information, as described on the expected outcomes.

4. Expected Outcomes

The expected outputs of the solution proposed to be developed are the following:

- Attractive and interactive application with different colours displayed to better show the info;
- Identify all coordinates systems;
- Show the Astronavigation triangle.
- Show the prime meridian (Greenwich meridian) in celestial sphere;
- Apparent motion of the sun, moon and stars in real time speed or faster mode, for see the apparent motion of 24 hours in 1 minute.
- The ecliptic with the position of the 4 reference points;
- Show the Zodiac;
- Solar and Lunar Eclipse in the position they happen.

5. Budget

The solution will have a 15,000€ budget to cover the proponent’s costs. The project will have a 3,000€ budget for hardware procurement, but this cost will be met by the tenderer independently of HR funding. The proponent will choose the most suitable software and hardware for the success of the challenge. The proponent will provide full details (brand, model, supplier, and cost) of hardware procured for the project.



The Celestial Equator System of Coordinates:

The familiar graticule of latitude and longitude lines, expanded until it reaches the celestial sphere, forms the basis of the celestial equator system of coordinates. On the celestial sphere latitude becomes declination, while longitude becomes sidereal hour angle, measured from the vernal equinox.

Declination is the angular distance measured along the hour circle, between a celestial body and the celestial equator. It ranges from 0° to 90° to North or South, and corresponds to observer’s latitude (north or south).

Polar distance is angular distance from a celestial pole, or the arc of an hour circle between the celestial pole and a point on the celestial sphere. It is measured along an hour circle and may varies from 0° to 180°, since either pole may be used as the origin of measurement. It is usually considered the complement of declination, though it may be either 90° – declination or 90° + declination, depending upon the pole used.

Sideral Hour Angle (SHA) is the angle about the celestial pole between the celestial meridian of the first point of Aries and the celestial meridian of the body, measured westward from the celestial meridian of the first point of Aries.

Right Ascension is a coordinate on the celestial sphere that is similar to, but not identical to, longitude on the Earth's surface. Right ascension measures the positions of celestial objects in an east-west direction, like longitude, but unlike longitude right ascension is a time-based coordinate.

The Horizon System of Coordinates:

The second set of celestial coordinates with which the navigator is directly concerned is based upon the horizon as the primary great circle. The line where Earth and sky appear to meet is called the visible or apparent horizon.

With the definition of the celestial horizon (90º plan from line Zenith / Nadir). The geographical position of the observer (Latitude), it’s the position Zenit in Celestial Sphere.

At this moment all star above the celestial horizon, have positive altitude and bearing and they are visible. All stars below the celestial horizon have negative altitude and they are not visible.

This system is based upon the celestial horizon as the primary great circle and a series of secondary vertical circles which are great circles through the zenith and nadir of the observer and hence perpendicular to his or her horizon. Thus, the celestial horizon is similar to the equator, and the vertical circles are similar to meridians, but with one important difference. The celestial horizon and vertical circles are dependent upon the position of the observer and hence move with changes position.

Altitude is angular distance above the horizon. It is measured along a vertical circle, from 0° at the horizon through 90° at the zenith. Altitude measured from the visible horizon may exceed 90° because of the dip of the horizon. Altitude is nominally a positive value, however, angular distance below the celestial horizon, called negative altitude, is provided for by including certain negative altitudes in some tables for use in celestial navigation. All points having the same altitude lie along a parallel of altitude.

Zenith distance is angular distance from the zenith, or the arc of a vertical circle between the zenith and a point on the celestial sphere. It is measured along a vertical circle from 0° through 180°. It is usually considered the complement of altitude. For a body measured with respect to the observer's horizon. One of these poles (having the same name, N or S, as the latitude) is above the horizon and is called the elevated pole.

The horizontal direction of a point on the celestial sphere, or the bearing of the geographical position, is called azimuth or azimuth angle depending upon the method of measurement. In both methods it is an arc of the horizon (or parallel of altitude). It is true azimuth (Zn) if measured east from north on the horizon through 360°

To calculate the Altitude, Zenith Distance and Bearing, must be calculate the Local hour angle (LHA). Local hour angle (LHA) is angular distance west of the local celestial meridian, or the arc of the celestial equator between the upper branch of the local celestial meridian and the hour circle through a point on the Celestial sphere, measured westward from the local celestial meridian, through 360°.

Between these two extremes, the apparent motion is a combination of the two. On this oblique sphere, circumpolar celestial bodies are those that remain above the horizon during the entire 24 hours, circling the elevated celestial pole. The portion of the sky where bodies are circumpolar extends from the elevated pole to approximately the declination equal to 90º minus the observer's latitude.

The ecliptic:

The ecliptic is the mean path of the Sun through the heavens arising from the annual revolution of the Earth in its orbit and appears as a great circle on the celestial sphere. The ecliptic is currently inclined at an angle of about 23°27' to the celestial equator. This angle is called the obliquity of the ecliptic and is due to the inclination or tilt of Earth's rotational axis relative to its orbital plane.

The ecliptic and the four main points (Winter and Summer Solstice, Spring and Autumn Equinox).

The Zodiac:

The zodiac is a circular band of the sky extending 8° on each side of the ecliptic. The navigational planets and the Moon are within these limits. The zodiac is divided into 12 sections of 30° each, each section being given the name and symbol (“sign”) of a constellation. The names were assigned more than 2,000 years ago, when the Sun entered Aries at the vernal equinox, Cancer at the summer solstice, Libra at the autumnal equinox, and Capricornus at the winter solstice.


If the orbit of the Moon coincided with the plane of the ecliptic, the Moon would pass in front of the Sun at every new Moon, causing a solar eclipse. At full Moon, the Moon would pass through the Earth’s shadow, causing a lunar eclipse. Because of the Moon’s orbit is inclined 5° with respect to the ecliptic, the Moon usually passes above or below the Sun at new Moon and above or below the Earth’s shadow at full Moon. However, there are two points at which the plane of the Moon’s orbit intersects the ecliptic.

These are the nodes of the Moon’s orbit. If the Moon passes one of these points at the same time as the Sun, a solar eclipse takes place.

The Sun and Moon are of nearly the same apparent size to an observer on the Earth. 


More information about the challenge:



Applications to this challenge are not allowed because the call is already closed.