Digital Sundial with Bright Wandering Time Scales

Technical Field

My invention is a digital sundial based on bright wandering time scale(s).

The invention is applied for visual time signalling and for teaching astronomy and descriptive geometry.

Background Art

Mankind for nearly 3500 years has provably known and used the sundial (in the following: "classical sundial") of which numerous imagined and realized versions have been formed, having, however a common principle: the position of the natural shadow cast by a stick (or an edge or a chord or a point etc.) or that of the light spot projected by a sun beam passing through a hole or a gap, can be read as index on a fixed time scale (or family of time scales). (See e.g. the newest comprehensive lecture collection: "19. Sternfreunde-Seminar 1991: Sonnenuhren", pp. 1-166, published by the Osterreischer Astronomischer Verein, Wien 1991.) The classical sundials have two basic deficiencies.

The visible angular diameter of the Sun cannot be neglected, and both the shadow index and the light spot index are in sunlit surroundings, making the pupils of the eyes also contract, and owing to all these, the shadow or the light spot neither in tones nor in contour line can be sharp enough, so the accurarcy of reading is not satisfactory, presenting the first deficiency of the classical sundials.

Another deficiency of the classical sundials is that the orbiting angular speed of the Earth about the Sun is fluctuating during the year, and the sundial's time with respect to the local mean time can show a deviation up to 16.5 minutes. To obtain an accuracy to the minute, expensive and complicated solutions have been elaborated, however, due to the deficiencies of the technology, their realizations are more

inaccurate. The change-over between the standard and summer time, and also the some- minute-adjustments, if done at all, take place with faulty principles, as it can be realized satisfactorily only in the equatorial sundial, which is however a tender, fragile structure. This is why adjustable classical sundials hardly. can be met in practice.

Disclosure of the Invention

The aim of my digital sundial according to the invention is to realize the aims and to eliminate the said deficiencies of the classical sundials and to produce an easily erectable and adjustable device. More particularly, the object of the present invention is to show the time in such places, for example, where people do not or reluctantly wear a watch, as in the garden, or on the beach, however, the invention can be utilized in other public or private places and buildings, and also any construction for other purposes (for example a gate) can be formed as a digital sundial, while its small, even tiny variants can be of portable execution as well. The invention is always suitable to indicate the local "natural time" or any other time deviating from that with a constant value, (e.g. local time of another place), moreover, provided with several time scales it can be applied for simultaneous signalling of the local times of various geographical places, where the "natural time" means the time that shows 12 o'clock when the Sun (on the geographical meridian of the sundial or on a different meridian) is at culmination. The adjustable variants of the digital sundial can be adjusted for showing various times (various civil times, standard time, daylight saving time, "private time", local mean time of other geographical places etc).

Another object of the digital sundial according to the invention is to facilitate the explanation of the relative movement of the Sun and the Earth, the elements of astronomical geography etc. with its using as an educational aid. The culmination, the sunrise and sunset, the equinox, the solstices, the planes of the ecliptic and the equator, the axis of the Earth, the axis of the universe, the Polaris and, on the northern hemisphere, the position of the northern direction; on the southern hemisphere the position of the southern direction, the concepts of the latitude and longitude and the interrelationships of all these can be explained by the position of the index line, the transparent time scale and the bright wandering time scale, each to be described later. Through the seasonal deviations, the bright wandering time scale, resp. its wandering

velocity and direction, promotes to understand the phenomena of the celestial mechanics, resp. to orientate in the solar system and in the universe for the students, relating not only for the place of the sundial but - with adjusting the sundial for other longitudes and latitudes - to any point of the Earth, as well. A special advantage of the adjustable variant according to the invention relating to the classical sundials in the education is in that the signalled time can be easily, with one or two movements adjusted and readjusted, so enabling a quick illustration of the movement of the Sun and the Earth relative to each other as well as of the various time systems. So - in the non-adjustable and the adjustable variants to different degree - developing the space-perception of the students, as an additional object is fulfilled, i.e. , e.g., promoting the education of the descriptive geometry as well, because the spatial position of the Sun and the Earth relating to any position of the sundials has to be imagined and can be given even as a drawing task too.

Besides the above-mentioned objects of time signalling and education, the invention can be utilized for other purposes, too, which however, also comprise first of all the visual time signalling.

The basic task to be solved by the digital sundial is the visual signalling of the time, valid at some place (not necessarily at the erection place) including in the adjustable variants the required readjustments from time to time, and enabling the reading in the whole sunny part of the day (in spring and summer more than daily 12 hours, in the polar summer even 24 hours).

The basis of the digital sundial according to the invention is the recognition that if not a wandering shadow- or light index or a shadow mark of small extent is projected to the fix time scale or family of time scales (e.g. analemma-network), where in the strong diffused illumination the cast shadow or the projected light marks weaken but through a (family of) transparent time scale(s) a (family of) bright wandering time scale(s) comprising bright time marks (for example spots or strokes) and signs (for example digits; this is why the device is called "digital sundial") is projected to a viewing screen being in shadow resp. to the index line marked thereon, then the projected bright wandering signs and marks will appear in tone and contour much sharper and therefore more accurately readable on the surrounding shaded surface, than in the case of the classical sundial.

The invention is described in detail with the aid of two examples, illustrated in the following drawings enclosed:

Fig. l. shows the perspective view at 2 o'clock p.m. of a rigid variant of the embodiment of the digital sundial according to the invention, readable from above directly,

Fig.2. shows the longitudinal section A- A of an embodiment of the digital sundial according to the invention adjustable in every respect, readable from below directly and from a mirror indirectly,

Fig.3. shows the view of the embodiment of Fig.2 from the direction of the culminating Sun showing the bright wandering time scale in the mirror.

The digital sundial according to the invention comprises three requisit geometrical formations: an index line 1, a transparent time scale 2 (or family of transparent time scales) and a viewing screen 4, which all are naturally supported by various supporting members. After the erection of the digital sundial to be described later the index line 1 is parallel with the rotation axis of the Earth and the non- transparent or translucent (semi transparent) viewing screen 4 lies on it. A non- transparent scale surface 5 covers the scale wall 16 so that it shades a considerable part or the whole of the viewing screen 4. The necessarily non-transparent scale surface 5 (and if non-transparent, also the scale wall) is interrupted by the time signs 6 and the time marks 7 of the (family of) transparent time scale(s) 2, and through them the beams of the Sun fall on the viewing screen 4 shaded by the scale surface 5, realizing thereby the bright (family of) wandering time scale(s) 3 in accordance with the change of direction of the radiation of the Sun. The time signs 6 and marks 7 of the (family of) bright wandering time scale(s) 3 falling on the index line 1 show the just valid pont of time.

The index line 1 is the common line of intersection of the imaginery meridian semiplanes 9, which deviate from each other with constant meridian angle 8 difference, on whose lines of intersection with the scale surface 5 comprising the (family of) bright time scale(s) 2 the transparent time marks 7 of the transparent time scale(s) 2 lie. The transparent time marks 7 belonging to round hours follow each other with the meridian angle 8 difference of 15°, i.e. the meridian angle 8 density of the transparent time scale(s) 2 is 15°/hour= 0,25°/min, except if the optical inhomogenity of the medium

between the Sun and the viewing screen 4 cannot be neglected, e.g. if the invention is used under clear water. In this case the meridian angle 8 differences are calculated with considering the refraction of light. The form and location of the scale surface 5 is such that it shades the viewing screen 4 and has one single line of intersection with any of the meridian semiplanes 9, at least within the strip comprising the transparent time scale(s). So, the scale surface 5 can be of highly optional formation (plane, prism, pyramid, even not rectifiable surfaces), but mostly is a surface of revolution (cylinder, cone, sphere, or surface of revolution of optional meridian curve), whose geometrical axis is the index line 1, while the transparent time marks 7 and signs 6 are arranged in the scale surface 5, mostly along its intersection with some plane, perpendicular to the index line 1, however, these marks 7 and sign 6 can be slided along their own meridian lines, too, independently of each other.

In fixed position, one single transparent time scale 2 can cast only the local (natural) time to the index line 1 with accuracy. The civil time is shown with accuracy only if the transparent time scale 2 is readjusted from time to time, or various transparent time scales 2 are constructed for the various periods of the year. In this case it can be expedient to substitute a family of transparent time scales (e.g. analemma network) for the transparent time scale, a point of whose bright wandering line belonging to the just valid moment of time is cast always to the same point, the so called index point of the index line 1, where it can be read. Though to draw the whole index line 1 would be unnecessary for reading the time, but knowing its position for constructing the family of transparent time scales and for erecting the invention on the spot remains necessary further.

The above geometrical formations are realized in the invention as follows: The viewing screen 4 is the surface of a - mostly plate-shaped - viewing body

15. The index line 1 is a scratched resp. drawn, dyed, or printed line on it. If the viewing screen 4 is not transparent, the time can be read more or less with back to the sun, i.e. (on the northen hemisphere) looking from the direction South-East, South, South-West. But, if the viewing screen 4 is translucent (semi-transparent) and at the same time the viewing body 15 is a transparent planparallel plate, the reading can take place best more or less facing the Sun, i.e. from the direction North-West, North, North-East. By the aid of the mi ^r 10 put near the viewing screen 4 with a suitable inclination, the most favourable du'ection of reading can be changed, increasing hereby

the freedom of placement of the digital sundial according to the invention. The transparent time signs 6 (e.g. numerals) of the transparent time scale 2 have to be positioned so (upright, inverted or reversed position) that from the direction of reading, the image 3a of the signs of the bright wandering time scale 3 should be seen in upright and non-reversed position, while the order of the transparent signs themselves should follow the East to West direction, i.e. the direction of the increasing in value of the signs on the transparent time scale 2 for the northern hemisphere is opposite to that for the southern hemisphere.

In the adjustable variants of the digital sundial according to the invention a screen shaft T3, consisting of one or two parts, supporting the viewing body 15 but not covering the index line 1, is positioned concentrically with the index line 1. The viewing body 15 together with the viewing screen 4 can be tilted about the screen shaft T3. The mostly lamina-like scale wall 16 can be of transparent material, which is covered by a non-transparent or hardly translucent scale surface 5, except the transparent time marks 7 and the transparent time signs 6 and some possible transparent figures or wordings. The scale wall 16 can be made also of non-transparent or hardly translucent material, in which the mentioned figures can be formed by perforation (boring, engraving, milling, cutting, punching etc.). The scale wall 16 with the transparent time scale(s) 2 on it is turnable about the scale shaft T2 consisting of one or two parts and concentric with the index line 1 and the screen shaft T3. If the scale wall 16 and the viewing body 15 form one single rigid unit, both of them can be turned about a common shaft whose geometrical axis coincides or is parallel with the index line 1.

The elevation angle of the the index line 1 related to the horizontal plane can be regulated by tilting the screen shaft T3 about the horizontal axis Tl . The horizontal axis Tl is perpendicular to the index line 1 as well as to the screen shaft T3. The placement of the horizontal axis Tl and its requisite is such that they do not make any obstacle against projecting and/or viewing the bright wandering time scale(s) 3.

All of the shafts Tl, T2, T3 can be fastened either by tight fitting or by the aid of separate unfastening-adjusting-fixing elements (screws, springs etc.) in the required position. Instead of the shafts Tl, T2, T3 also circular sliding or roller rails with the same geometrical axes can be applied.

The assemblage of the described parts of the invention completed by a levelling plate 11 (or a tribrach), i.e. the so called superstructure 12 can be erected on a stage 13 (e.g. a simple horizontal table or other kind of supporting body) or it can be pulled over to a vertical pivot 14, on resp. about which the superstructure 12 can be turned into the adequate position, where it can remain due to its weight, or can be fixed by one or two screws. The superstructure 12 of a sundial for a constant place, however, can be adjusted more precisely and fixed more reliably, namely the stage 13 or other supporting body resp. the vertical pivot can be mounted by feet screws or with a ball- and-socket or a cardan joint system to a base body of column, wall or bracket type. An interesting variant of the invention is where an outside surface (floor, wall, etc.) serves as viewing screen 4. In this case the index line 1 is embodied by a non- transparent strip drawn on a transparent planparallel plate, or by an independent string or rod, and in the scale surface 5 and in the scale wall 16 transparent bands are positioned ensuring the continuous projection of the shadow of the index line 1 onto the outside surface on which coincidence of a time mark of the bright wandering time scale 3 with the shadow of the index line 1 shows the actually valid point of time.

If on the viewing screen 4 optionally on the index line 1 a photocell is placed, it is possible to operate some electric device (bell, tape player) by it , while a separate transparent time mark 7 projecting light onto the photocell in a required period is located on an adequate place of the scale surface 5.

It is possible furthermore by the aid of mounting several superstructures 12 to the common levelling plate 11 or to the stage 13 resp. to the base body to show simultaneously various local times (winter, summer, natural etc.) resp. the time of other geographical places (i.e. Central European time, universal, or Greenwich mean time, time of New York, time of Tokyo etc.).

In order to make visible the Sun's beams the sundial can be completed with nozzles introducing fog or smoke or fine floating particles into the space between the transparent time scale(s) 2 and the viewing screen 4.

To protect the most sensitive part, i.e. the superstructure 12, of the invention from the rain, dust, hits etc., an instrument housing with transparent wall is mounted e.g. to the levelling plate 11 or to the stage 13 or to the base body or only around the scale wall 16; through whose wall some members (screws, rods etc.) penetrate, according to necessity, enabling to adjust the sundial from outside.

To protect the sundial device from the effect of thermal expansion the base body

(e.g. a column) can be surrounded with a cover made of materials of low thermal conductivity suitable for protecting and ventilating the base body and equalizing its temperature. The cover can be formed also so that it serves as a self-ventilating base body as well.

To facilitate the erection and adjustment of the sundial it is expedient to provide the sundial with a measuring rod or an angle meter, and a bubble-tube or a plumb.

The digital sundial according to the invention has to be erected so that the index line 1 should be parallel with the rotation axis of the earth. It can be realized e.g. so that the upper plane of the levelling plate 11 (or tribrach) of the sundial is set horizontal, and checked by a bubble-tube directly, or by checking the verticality of the support ears 17 by a plumb. After that the index line 1 will be tilted around the horizontal shaft Tl until its elevation angle is equal to the geographical latitude φ of the erection place and then it will be fixed. (The most expedient adjustment of the angle φ depends on the type of the embodiment of the invention.) Then the (family of) transparent time scale(s) 2 with the scale surface 5 will be turned into the natural position: i.e. the transparent time mark of 12 o'clock should be in the vertical plane lying on the index line 1. After that, the levelling plate 11 together with the superstructure 12 will be rotated about an imaginary vertical axis or the vertical pivot 14 until the mark of the bright wandering time scale 3 falling on the index line 1 shows just the local natural time. The relationship between the local natural time t _L and the standard time V- ts= t _L - [ e + 4 (λ _L - λs)], wherein λ and λs are the geographical longitudes east from Greenwich of the local geographical meridian and the standard time meridian, resp., in degrees and tenths of degree, the unit of the coefficient "4" is min/° (= minute/degree). The "equation of time" e= t^t , is the fastness (if negative: slowness) of the Sun as compared to the local mean time t^ in minutes and tenths of minute, which can be found as function of the calendar day in the instructions to be attached to the sundial. ^ and tg are substituted in hours and minutes. In case of summer time (daylight saving time) one hour should be added to the above calculated value of tg. Without any further adjustment the sundial will always show accurately the local natural time, so 12 o'clock will be shown when the Sun culminates at the place of erection.

If some mean time (standard time, summer time, private time) valid either on the erection site or at any other geographical place is requested to be shown by the digital sundial, then the transparent time scale(s) 2 together with the scale wall 16 has to be turned from the aforetreated position until the bright wandering time scale 3 shows just the requested time in the moment of adjustment. However, as the fastness and slowness of the Sun during the year changes (extreme values: on 3rd November + 16 min 24 s, on 12nd February -14 min 16 s), the sundial - in accordance with the required accuracy - has to be adjusted from time to time by readjusting the transparent time scale(s) 2. The necessary frequency of readjustment depends on the calendar season: sometimes days, sometimes weeks can pass without need of readjustment if the requested accuracy is ± 1 minute. The necessary frequency of the readjustment can be judged from the equation of time, however, it is enough to compare the sundial's time with the valid civil time signalled by the radio or shown by a correct watch.

The extent in meridian angle 8 of the transparent time scale(s) of the digital sundial according to the invention can be wider than 180°, i.e. more than 12 hours, if the viewing screen 4 can be tilted around the screen shaft T3 while the scale shaft T2 and consequently the transparent time scale(s) 2 remain fixed. If the viewing screen 4 is tilted facing the rising Sun in the early hours, the sinking Sun in the late hours, the time can be read during the whole sunshine period of the day (in the polar zones in summer during 24 hours).

The recounted adjustment possibilities need not be used in every case. A sundial used only for showing the local natural time in a constant place for not more than about ten hours a day is not to be readjusted. In this case, it is enough to build the index line 1 in the local geographical meridian plane with an elevation angle equal to the local latitude φ _L , to build the transparent time scale 2 in the natural position, and the viewing screen 4 for showing the time in the requested 10 hour period, (i.e. from 6 hours to 16 or from 9 to 19 hours). This is a rigid unadjustable embodiment of the sundial. After erection the sundial always accurately shows the natural time (according to which the nature - if not influenced by man - rises, lives, sets). Between the fully adjustable and the fully unadjustable sundial there can be various transitions. For example, if in a health resort or on a beach, visual time signalling is needed only with the accuracy of +2 minutes in the summer holiday period (as between 25 June and 25 August, when the movement of the Sun deviates from a

mean time only +2 minutes), then a completely fixed rigid sundial can be erected without any readjusting possibility. If in the whole year the accurate time is required in a constant place for a shorter daily period than 10 hours, in this case it is enough, if the viewing screen 4 and the scale wall 16 are rigidly fixed to each other and can be readjusted together about the index line 1 or about a common shaft parallel to that. If in a certain place, showing the natural time is required for more than 10 hours, then the viewing body 15 has to be tiltable about the rigidly fixed index line 1, and if the required accuracy is about ±15 minutes, then any readjustment possibility for the scale wall 16 is superfluous. The table of equation of time gives information on the deviation of the local natural time from the local mean time for all days of the year, and considering also the accuracy requirements, it can be decided whether the scale wall 16 should be readjustable or it can be fixed.

The main advantages of the digital sundial according to the invention are as follows: a/ it enables showing (visual signalling) the time as function of the Sun's apparent movement on the basis of a new recognition, b/ the time is shown by bright and sharp time scale(s) wandering on a well shaded viewing screen, thereby increasing the accuracy of reading in comparison with the sundials known till now; c/ for the correct erection of the digital sundial, besides knowing the latitude φ, the longitude λ, and the value of the equation of time e on the day of erection, such simple aids are enough as e.g. a measuring rod, a weight hanging on a string and a correct watch; d/ the adjustable variants of the digital sundial can be adjusted and readjusted with one or two motions for any kind of time system, their accuracy meets all the requirements of the everyday life, and they function during the whole sunshiny period of the day; e/ on the common principle an inexhaustible variety of embodiments of the sundial is realizable; f/ the digital sundial is suitable as educational aid in teaching astronomy and descriptive geometry.

List of Symbols

1 index line la virtual image of the index line

2 (family of) transparent time scale(s)

3 (family of) bright wandering time scale(s)

3a virtual image of the (family of) bright wandering time scale(s)

4 viewing screen

5 scale surface

6a transparent time sign readable on the viewing screen from above

6b transparent time sign readable on the viewing screen from below

7 transparent time mark

8 meridian angle

9 imaginary meridian semi plane

10 mirror

11 levelling plate

12 superstructure

13 stage

14 bore of vertical pivot

15 viewing body

16 scale wall

17 support ear

S direction of sun beams

Tl horizontal shaft

T2 scale shaft

T3 screen shaft λ geographic longitude φ geographic latitude