GB2033578A - Teaching aid for astro-navigation and navigational astronomy - Google Patents

Abstract

A teaching aid for astro-navigation and navigational astronomy comprises a member, such as a panel 1, having a surface 1a bearing a scale of degrees 4 along edges 1b and 1c and a pin 3 projecting normal to surface 1a. The panel is supported so that it rests vertically on a baseboard 5. The altitude of the sun or other celestial body can be determined from the position of the shadow of the pin 3 as cast by light from the body on the surface of the baseboard 5 or on a surface 7 when disposed adjacent the scale of degrees 4, or by use of a sighting-means used in conjunction with the pin. <IMAGE>

Description

SPECIFICATION Teaching aid for astro-navigation and navigational astronomy The present invention relates to a teaching aid for navigational astronomy and astro-navigation, otherwise known as celestial navigation.

Astro-navigation is a subject which is commonly taught to professional navigators as a means of navigating ships and aircraft of all kinds. It is also a subject which is of increasing interest to amateur navigators such as amateur yachtsmen. Additionally, it is a subject, together with navigational astronomy, which may be taught in schools and colleges.

However, although the principles of astronavigation can readily be taught in a classroom, it is often extremely difficuit for students of the subject to put their acquired knowledge into practice in order to try out the theory which they have learnt in the classroom. Since astro-navigation is essentially a scientific art which requires progressive practical application in order to become competent at the subject, this is a grave disadvantage.

Thus, at the present time, in order to practice astro-navigation it is not only necessary to have a relatively expensive instrument, namely a sextant, at one's disposal but an even greater obstacle arises from the fact that very many students of astronavigation learn the subject at a location remote from the sea whereas it is generally desirable to be situated at the sea in order to have a horizon available so that practical astro-navigation can be carried out. Moreover, even if a student of the subject takes the trouble to travel to the sea, his attempts to carry out practical work on the subject may well be thwarted due to weather conditions making the horizon too indistinct for any observations to be made or else due to cloud obscuring the heavens and, more generally the sun.

The only other alternative available at present, of trying to create an artificial horizon by means of a container of mercury or viscous fluid is often unsatisfactory in practice, has altitude limitations and requires a sextant to be used.

The present invention provides a self-contained teaching aid for astro-navigation which enables a student of the subject to gain practical experience of determining the altitude, bearing and movements of celestial bodies, and more particularly the sun, at any location on land no matter how remote from the sea and without requiring a clear horizon, artificial horizon or a sextant, bubble type or otherwise.

From one aspect the invention provides a teaching aid for astro-navigation comprising a member hav- ing a primary surface associated with a scale of degrees located at a boundary of said surface, means for maintaining the primary surface in a vertical plane, a pin projecting from said primary surface and normal thereto, and at least one further surface arranged at or disposable along said boundary of said primary surface and adjacent to part of said scale of degrees.

Advantageously the member may be in the form of a board or panel having a flat surface which can be maintained in a vertical plane by means of a support attached to or integral with the board or panel and at right angles thereto. An edge region of the board or panel is calibrated in a scale of degrees over an arc centred on the pin which projects normal to said surface. The calibration is so disposed as to indicate the elevation of a celestial body whose light falling on the pin casts a shadow of the pin on the further surface adjacent the scale. The latter surface disposed along at least one edge of the board or panel may either be formed by part of a separate member or else may be formed by a flange-like projection substantially normal to the board or panel.

In order satisfactorily to use the teaching aid, it must be disposed so that a line passing through the pin and the zero altitude point on the scale is in a truly horizontal plane and therefore preferably the apparatus also includes a base or baseboard which is adapted to be levelled so that it is truly horizontal in all directions. Such levelling can either be achieved with the aid of a separate spirit level and the use of packing pieces under the base or baseboard or, alternatively, the apparatus may be provided with its own built-in level for indicating the truly horizontal position.

From another aspect, the invention provides a method of determining the altitude of a celestial body capable of causing a shadow to be formed, which consists in disposing a first surface in a vertical plane aligned with the body and so that the line passing through a pin projecting normal to said first surface and a point representing zero altitude is horizontal, and detecting the shadow of said pin as cast on a second surface which is itself disposed in relation to said first surface such that said shadow can be read against a scale calibrated in degrees representing said altitude of said celestial body.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which: Figure 7 is a perspective view of one embodiment of altitude finder according to the invention, and illustrates its mode of use, and Figures 2, and 3 are perspective views of further embodiments.

Figure 1 shows a simple embodiment of apparatus forming an altitude finder intended as a teaching aid for astronavigation. The apparatus, generally indicated atA, comprises a square panel 1 disposed in a vertical plane and supported in this plane by means of a flange 2 secured along the edge of which the panel rests. A short pin 3, e.g. about 4 inch long, is mounted to project normal to one surface la of the panel and at least part of the lower edge 1b and one vertical edge 1 C of the panel are marked as a scale 4 representing degrees altitude over at least an arc of 900 subtended by the pin3.

The device so far described is intended to be mounted on a truly horizontal surface and to this end, the apparatus includes a rigid baseboard 5 which can be accurately levelled in a horizontal plane either by means of a separate spirit level, or by means of a built-in spirit level such as is indicated at 6. In addition, the apparatus includes a strip member 7 having a surface which can be disposed along the vertical edge 1c of the panel which bears the 0-45 degree portion of the scale. The strip member 7 is shown adjacent the opposite edge for convenience of illustration.

The panel 1, baseboard 5 and strip member 7 are made of a rigid inert material having a flat smooth surface. One suitable material is a plastics covered chipboard which is preferably of a white or light colour so that a shadow cast thereon can be easily seen.

In use, the baseboard 5 is placed on a firm support, such as a table, and is levelled by means of a spirit level and packing pieces until it is truly horizontal.

The accuracy of the altitude finder depends largely upon the accurate levelling of the baseboard. The actual altitude finder formed by the panel 1 is now stood upright on the baseboard and the plane of the panel is generally directed towards the sun S until the shadow of the pin 3 appears on the baseboard or, if it is being cast off the vertical edge icofthe panel, until the shadow can be obtained on the surface of the separate strip member 7 held against the vertical edge 1c. In practice, if the sun's altitude is less than 45" it will be necessary to use the separate strip 7 in order to determine the position of the shadow of the pin, whilst if the altitude of the sun is greater than 45" the use of this member will not be necessary since the shadow of the pin will fall on the baseboard.

The position of the altitude finder is now accurately adjusted so that the vertical surface la carrying the pin 3 is in a plane directed towards the sun i.e. so that the shadow of the pin cast on the baseboard 5 or the strip member 7 is as nearly as possible the same length as the pin. The altitude of the sun can now be read by the position of the shadow against the scale 4 on the panel. The most accurate reading is obtained by measuring the reading at the centre of the base of the shadow when it is on an integral degree and this position may either be judged by eye or with the assistance of a sharp point, such as a pencil point with considerable accuracy.

Once altitudes of the sun have been obtained at instants of time, the position of an observer can be determined in the normal way with the aid of an appropriate almanac, tables and calculations available to students of astro-navigation.

According to a modification of this embodiment, the pin 3 is disposed at one corner of the panel 1, as shown in dotted lines at 3a, and the scale 4then extends further along the edges 1b and ic of the panel.

Besides obtaining readings of the sun, the apparatus of the invention may also be employed for taking altitude readings of other celestial bodies, such as the moon, stars and planets. For such applications the panel may be provided with a plumb line and weight for setting up the apparatus, and a sighting means which is used in conjunction with the pin for determining the altitude of the celestial body. For such uses, the panel is held in the hand or may be conveniently supported.

Figure 2 shows a further embodiment of altitude finder according to the invention in which the various parts of the device as described with reference to the embodiment of Figure 1 are all connected together to form a single unit. Thus, in this embodiment the device comprises a vertically upstanding panel in the shape of a quadrant 10 supported by a vertical pillar 11 mounted on a horizontally extending base 12. The base not only serves to support the panel in a vertical plane but also incorporates a spirit level 13 by means of which the base can be levelled. To this end, the base is provided with feet 14, each of which is in the form of an adjusting screw whereby the base may be accurately levelled when resting on a surface, such as a table. As previously, the panel is provided with a pin 15 projecting normal to one surface and located at the apex of the quadrant.The arcuate edge of the quadrant is provided with a flange 16 on which the pin can cast a shadow when the panel is correctly orientated in a plane directed towards the sun. The arcuate edge of the panel also bears a scale 17 calibrated in degrees, as previously described, so as to provide an indication of the altitude of the sun as represented by the shadow of the pin cast on the flange against the degrees scale.

In order to align the panel 10 in the correct plane after the base has been levelled, the pillar 11 is mounted so as to be rotatable about an axis normal to the base 12, e.g. by mounting it on a spindle extending into the pillar.

The apparatus may be made of similar materials to the embodiment of Figure 1.

Figure 3 shows another embodiment of altitude finder which is generally in the form of a cube 20 and which may be moulded from a rigid plastics material. The upper surface of the cube is provided with a spirit level 21 to assist in levelling the device in a horizontal plane and one side face 20a of the cube forms the operative plane which is directed towards the sun. A pin 22 projecting normal to surface 20a is located at an upper corner of this surface and the two opposite edges of the cube are marked as a scale 23 calibrated in degrees between 0 & 90 .

These edges of the cube may either be provided with projecting flanges (not shown), as described with reference to the Figure 2 embodiment, on which the shadow of the pin may be cast; or alternatively the cube may be used with a separate baseboard and strip member on which the shadow is cast, as in the embodiment of Figure 1.

If desired the pin may be mounted in the centre of the face 20a as indicated in broken lines at 22a. In this case the scale 23 need only extend part way along each of the edges of face 20a.

It will be seen that the apparatus according to the present invention provides an inexpensive and effective teaching aid for students of astro-navigation which enables them to conduct practical experiments, and in particular to determine the altitude of the sun, without the necessity either of purchasing any type of sextant or requiring them to be at sea or in a coastal location in order to obtain a satisfactory horizon.

Tests made with the instrument in use in order to determine position by means of measuring the altitude of the sun have shown mean and maximum errors which are quite acceptable for practice purposes and which are not all that significantly greater than the average errors obtained by many observers using a sextant in a similar way to determine their position.

Claims (21)

1. A teaching aid for astro-navigation comprising a member having a primary surface associated with a scale of degrees located at a boundary of said surface, means for maintaining the primary surface in a vertical plane, a pin projecting from said primary surface and normal thereto, and at least one further surface arranged at or disposable along said boundary of said primary surface and adjacent to part of said scale of degrees.

2. Ateaching aid as claimed in claim 1, in which the member is in the form of a board or panel having a flat surface which can be maintained in a vertical plane by means of a support attached to or integral with the board or panel and at right angles thereto.

3. Ateaching aid as claimed in claim 2, in which an edge region of the board or panel is calibrated in a scale of degrees over an arc centred on a pin which projects normal to said surface.

4. A teaching aid as claimed in claim 1,2 or 3, in which at least part of said further surface is a separate member disposed or disposable along at least the boundary of said primary surface adjacent to a part of said scale of degrees and normal thereto so that light falling on said pin can cast a shadow of the pin on said further surface adjacent the scale of degrees.

5. Ateaching aid as claimed in any preceding claim, in combination with a base member on which said member can be supported with the primary surface in a vertical plane.

6. Ateaching aid as claimed in claim 5, in which the base member incorporates a spirit level or other level indicating means.

7. Ateaching aid as claimed in claim 5 or 6, in which said base member includes means for levelling said member in a horizontal plane.

8. Ateaching aid as claimed in claim 1, in which said member having a primary surface is formed by an arcuate board or panel carrying a scale of degrees along at least part of its arcuate edge.

9. Ateaching aid as claimed in claim 8, in which said arcuate board or panel is provided with a flange along said arcuate edge normal to the primary surface of said board or panel, said flange forming said further surface on which a shadow of the pin can be cast adjacent the said scale of degrees.

10. A teaching aid as claimed in claim 8 or 9, in which the arcuate board or panel is mounted on a base member so that it can be rotated about an axis normal to the surface of the base member.

11. A teaching aid as claimed in claim 1, in which said member is in the form of a block, one of whose surfaces forms the primary surface bearing a scale of degrees along two of its adjacent edges.

12. Ateaching aid as claimed in claim 11, in which the block is in the form of a cube.

13. Ateaching aid as claimed in claim 11 or 12, in which a surface of the block incorporates a spirit level.

14. Ateaching aid as claimed in claim 11, 12 or 13, in combination with a separate member forming at least part of said further surface.

15. Ateaching aid as claimed in any preceding claim, in which the pin is disposed adjacent an edge or corner of the primary surface of the member.

16. A teaching aid as claimed in any of claims 1 to 15, in which the pin is located adjacent the centre of the primary surface of the member.

17. A teaching aid as claimed in any preceding claim, incorporating a plumb line and weight for setting the apparatus and a sighting means which is used in conjunction with said pin for determining the altitude of a celestial body.

18. A method of determining the altitude of a celestial body capable of causing a shadow to be formed, which consists in disposing a first surface in a vertical plane aligned with the body and so that the line passing through a pin projecting normal to said surface and a point representing zero altitude is horizontal, and detecting the shadow of said pin as cast on a second surface which is itself disposed in relation to said first surface such that said shadow can be read against a scale calibrated in degrees representing said altitude of said celestial body.

19. A method as claimed in claim 18, which includes the step of orientating said first surface in a vertical plane so that the shadow cast by said pin is substantially of the same length as said pin.

20. The method of determining the altitude of a celestial body substantially as hereinbefore described.

21. A teaching aid for astro-navigation substantially as hereinbefore described with reference to Figure 1 or Figure 2 or Figure 3 of the accompanying drawings.