GB2050775A - Digital Planetarium Display System - Google Patents

Abstract

A system is disclosed for providing a planetarium display from digitally stored data. A memory (M) contains digital data on stars and planets specifically representing such characteristics as location, intrinsic luminosity, colour and motion patterns, as related to time. A picture system (12) generates a selected display with respect to a selected viewpoint, which viewpoint may move in the universe to afford a dynamic display. Optical distortions resulting from projection on a spherical surface are corrected by electronic means (30, 39) in the data signals and colour is introduced by a colour control unit (C) to add another dimension to the display. The system incorporates data processing capability to indicate motion patterns of stars, not only to provide a dynamic display but also to indicate future or past relationships between individual stars. The system also affords special effects, accomplished as by computer- graphics clipping techniques, to realistically display planets. <IMAGE>

Description

SPECIFICATION Digital Planetarium Display System Background and Summary of the Invention Optical planetariums are widely used for projecting complex light patterns on a concave hemispherical surface to display celestial images that indicate the relative positions and motions of celestial bodies. Such planetariums have been developed to provide realistic celestial displays and to simulate views from various locations and at various times. Optical planetariums with such capability are mechanically complex and may include thousands of individual parts. The optics for such structures may also be quite expensive.

However, in spite of the cost and complexity attendant sophisticated systems, interest in planetariums runs high for a variety of uses.

Specifically, in addition to the usefulness of planetarium displays for astronomers, they are effective aids for the study of celestial navigation.

Furthermore, planetariums are useful to provide displays or shows for lay persons either for entertainment or introductory education.

Consequently, a substantial need continues to exist for an improved planetarium and particularly for a planetarium capable of accomplishing displays of greater realism and flexiblity. For example, the capability to provide a display simulating the rapid movement of the viewer through space or time affords exciting possibilities.

In general, the present invention is directed to a digital planetarium wherein celestial data is registered in a memory for selective processing by a picture system to provide a display. The system includes structure for electronically correcting distortions developed as a result of the wideangle projection of a plane image onto a spherical surface. Also, the system includes structure for varying the viewpoint of observation not only terrestrially but into space as well. The system incorporates a color capability for tinting stars from ranges of orange to blue. Additionally, the system enables effective time displacement for developing displays that are remote in time from the present.

Brief Description of the Drawings In the drawings, which constitute a part of this specification, an exemplary embodiment demonstrating the various objectives and features thereof is set forth as follows: Figure 1 is a block and schematic view of a digital planetarium system constructed in accordance with the present invention; Figure 2 is a schematic view of a projection pyramid, diagrammatically indicating an operational aspect of the present invention; Figure 3 is a block diagram of an input terminal for the system of Figure 1; Figure 4 is a diagrammatic representation indicative of a form of distortion corrected by the system of Figure 1; Figure 5 is a block diagram of a component of the system of Figure 1; Figure 6 is a diagrammatic representation indicative of an operational aspect of the system of Figure 1;; Figure 7 is a block diagram of still another portion of the system of Figure 1; Figure 8 is a block diagram of still one other portion of the system of Figure 1; Figure 9 is a plan view of an image registered in the system of Figure 1 to accomplish particular displays; and Figure 10 is a perspective view of another image registered in the system of Figure 1 to accomplish particular displays.

Description of Illustrative Embodiment As indicated above, a detailed illustrative embodiment of the invention is disclosed herein.

However, embodiments may be constructed in accordance with various forms, some of which may be rather different from the disclosed illustrative embodiment. Consequently, the specific structural and functional details disclosed herein are mererly representative, yet in that regard they are deemed to provide the best embodiment for purposes of disclosure.

Referring initially to Figure 1 , the concave surface of a hemispherical dome D is represented to receive a composite light projection which is generated by computer-graphic techniques and which is capable of exhibiting various celestial scenes, from different observation points, from moving observation points, and at various times.

The dome D in one embodiment of the present invention may approach 75 feet in diameter with the projected picture covering an area defined by approximately 1 60 degrees. Of course, the dome D actually constitutes the projection screen of a theater (in accordance with well known planetarium techniques) that is not illustrated in Figure 1. The dome D as symbolically represented in Figure 1 in actual practice would be of vast proportions in comparison with the remainder of the system which generates and projects the light images. In that regard, Figure 1 is not physically scaled.

The light image for projection on the dome D is provided by an image display and projection unit P which in one embodiment employs a wide angle lens along with a projection cathode ray tube. In the operation of the system, a calligraphic display is developed by the sequential formation of display elements (stars). Of course, the persistence-of-vision phenomena and the rapid operation of the unit P produce a composite scene in the mind of the viewer.

As the light for individual stars is projected from the unit P, a filter or color-control unit C imparts select color filtering to accomplish colors ranging from pale orange to pale blue. Providing color in the display on the dome D tends to improve realism and impart further dimension to the scene.

Considering the display data, it is to be understood that data is stored on each star to be displayed. Specifically, the data includes positional, dynamic, intensity, and color information on each star that is to be represented.

Such data is registered in a memory M (lower left, Figure 1).

The selection of data from the memory M and control of its processing is provided by an interactive terminal T (upper left, Figure 1) which may incorporate any of a wide variety of interactive components. Thus, an operator at the interactive terminal T provides commands through the terminal T which are interpreted and implemented by a computer graphics system G, to withdraw data from the memory M, process such data, and drive the projection unit P, along with the color-control unit C, to accomplish either a dynamic or static celestial display. As suggested above, a selected display is variable with respect to time and viewpoint. Such variations may be incorporated in the display to produce a dynamic or moving picture.For example, by moving the viewpoint in space from one location to another, a display is provided which indicates a relative motion pattern, simulating the view, as though one were traveling in space.

As another example of dynamic display, a motion picture may exhibit changes in the celestial scene resulting from either moving the viewpoint on earth or to account for motions by the starts. Accordingly, the system is capable of providing a wide range of displays, which have not generally been possible utilizing conventional optical planetariums.

Turning now to the data contained in the memory M, a specific information format is stored for each star. Specifically, the data elements for each star are as follows: X dimension X-positional data Y dimension Y-positional data Z dimension Z-positional data intrinsic luminosity data C color data AX dimension X-motion data bY dimension Y-motion data AZ dimension Z-motion data Al change in intrinsic luminosity data AC color change data (time) In general, the data employed for depicting individual stars is relatively simple because the stars are not given any defined shape or form.

That is, the data is simply scalar locations with relative color and light intensity levels, which are affected by the current viewpoint and the time of observation. Consequently, in accordance with the well known principles of computer graphics, data is selected from the memory M (Figure 1) for development as an image in accordance with the viewpoint specified through the interactive terminal T. The data selection is accomplished by a picture controller and processor 10 and after processing into picture signals, is supplied to a picture system 12. In accordance with well known techniques of computer graphics, the picture system 1 2 organizes the display signal data and provides periodic drive signals through certain circuits peculiar to the present system (discussed in detail below) to the projection unit P.

With respect to the system of Figure 1, it is to be appreciated that the basic operation and interrelationship of the terminal T to select data from the memory M that is processed and developed by the processor 10 and the picture system 12 to actuate the projection unit P is well known in the prior art as disclosed, for example, in Principles of Interactive Computer Graphics by William M.

Newman and Robert F. Sproull, published in 1973 by McGraw-Hill Book Company. Basically, commercial forms of systems capable of developing pictures from data elements, translating and rotating objects in such pictures, and accomplishing changes of viewpoint have been commercially available for some time, one form of which has been marketed by Evans 6 Sutherland Computer Corporation, Salt Lake City, Utah. Novel aspects of the present system are deemed to reside in the planetarium function and attendant structural modifications as will be apparent from the following description.

The display exhibited by the system of Figure 1 is symbolically represented in Figure 2.

Specifically, from a viewpoint 14, a viewer might observe a plurality of stars 1 6, recognizing of course that the entire display would in fact be carried on the concave surface of the dome D (Figure 1).

Recapitulating to some extent, as related to computer graphics, and data for the display of the stars 1 6 (Figure 2) is stored in the memory M (Figure 1) utilizing a data format as indicated above. Of course, various techniques may be employed for addressing the star data, for example, stars or displays may be addressed by common names of stars, sector coordinates, constellations, and so on utilizing conventional addressing techniques.

In composing a simulated display of the scene depicted in Figure 2, the picture controller and processor 10 (Figure 1) along with the picture system 12 incorporates means to accomplish data processing to effectively move the viewpoint 14 in relation to the stars 16, or to move the individual stars 1 6 in accordance with established motion patterns of the stars 1 6. Considering Figure 2, it will be apparent that if the viewpoint 14 is moved in relation to the stars 1 6, a dynamic display will be provided similar to the scene which might be observed from a spaceship moving along a path coincident to the change in viewpoint.

In developing a display to simulate the view as depicted in Figure 2, it will of course be appreciated that the data for the display is processed by various techniques including clipping as well known in the prior art and explained in U.S. Patent No. 3,639,736. In that manner, a pyramid of vision 20 generally represented in Figure 2, is defined and created in the form of digital data. Subsequently, the data is manifest as viewed in a single plane, e.g. on the face of a projection cathode ray tube in the image display and projection unit P (Figure 1). From the plane image, a display is projected onto the dome D which is essentially spherical.

For control purposes a display similar to the plane projection image developed by the projection unit P, is provided in the interactive terminal T as shown in greater detail in Figure 3.

Specifically, a cathode ray tube display 22 serves as an integral part of the interactive terminal Additionally, a keyboard 24 and a "joy stick" or control lever 26 are provided in the interactive terminal.

In the operation oe the system, the keyboard 24 may be employed to initially select the celestial sector to be viewed, thereby defining the clipping planes or the pyramid of vision 20 as illustrated in Figure 2. The details of structure for performing such operations are treated in greater length in the above-referenced book Principles of Interactive Computer Graphics.

After selecting a particular pyramid of vision, its four walls or clipping planes, as well as fore and aft clipping planes, may be shifted by actuating the control lever 26. Specifically, the control lever 26 may be manually moved to shift the clipping planes in any of the dimensions ), Y and Z.

As a further input device, the graphic display 22 incorporates a marker 28 as well known in the prior art for communicating selections or the like as manifest by the graphic display 22. For example, a specific star may be designated by the marker 28 along with an instruction to move the viewpoint toward such a star. Consequently, a wide variety of displays and exhibitions can be commanded by the components of the interactive terminal T.

As indicated above, the image displayed on the dome D is projected from a plane light image that is developed on the surface or face of a projection cathode ray tube (projection P, Figure 1). In translating the image from a plane surface to a spherical surface, certain distortions occur as illustrated in Figure 4. Specifically, for purposes of explanaion, assume a plurality of concentric annular lines as shown in Figure 4A, which divide the display into annular rings a, b, c, d.In projecting the image from a plane surface as represented in Figure 4A, onto a spherical surface, it can be appreciated that the outer (greater diameter) rings increase in width (though having a depth) in the sense that they must account for a larger surfacial area of the dome than the smaller inner rings.Although nat to scale, an indication of the increase in the width (Ar) of the illuminated area on the sphere by each of the rings is indicated in Figure 4 B. In substance, this criteria is related to an aspect of the present invention which involves recognizing that the plane image must be distorted somewhat to compensate for the inherent distortion resulting from projecting a plane image onto a spherical surface or viewing screen. Such distortion is accomplished by the deflection displacement circuits 30 (Figure 1). The circuits 30 are shown in greater detail in Figure 5.

The compensation of distortion in the deflection for both the X and Y dimensions is similar. In that regard, of course no deflection compensation is appropriate for the dimension Z.

As the circuits for attaining the compensation are similar for both the X and Y dimensions, a single compensation circuit is illustrated in Figure 5 for the X dimension compensation. A similar circuit would function to accomplish the Y dimension compensation.

The uncompensated deflection signal for both the X and Y dimensions are supplied from the picture controller and processor 10 through lines 32 and 33 to a radial distance computation circuit 34. The input signal in line 32 is also applied directly to an analog multiplier 36 while the output of the circuit 34 also is applied to the multiplier 36 after passing through a function-of-rmultiplier 38.

In the operation of the circuit of Figure 5, the X component deflection signal, e.g. ramp signal, is processed by the computation circuit 34 and operated on by the multiplier 36 to incorporate a non-linear increase in amplitude as the ramp progresses. Essentially, the purpose of the function generator circuit 38 is to introduce a decreasing rate of displacement by the ramp as the displacement increases. The resulting signal from the function generator 38 is stabilized in an multiplicative combination with the signal from the line 32 by multiplication in the multiplier 36.

Accordingly, a ramp or deflection signal is provided which is non-linear and accomplishes a decreasing rate of deflection with the extent of deflection so as to compensate for the projection from a plane to a sphere.

The translation of a plane image to a sphere also has an effect on the luminosity or brightness of stars in the display. Preliminarily, referring to Figure 2, it may be seen that the luminosity (brightness) of the stars, as represented, will depend upon different considerations. First, the data on each star includes information on the intrinsic luminosity, i.e. the data signal I provides such information. However, the apparent luminosity of a star will depend not only upon its intrinsic luminosity but additionally upon the distance between the star and the viewpoint of the observer. Accordingly, the distance from the viewpoint 14 (Figure 2) to the selected star 16, in accordance with the present invention, is scaled and the brilliance of the star in the display is accordingly adjusted.

To consider the operation of the system described herein in greater detail, reference will now be made to Figure 6 indicating a point 40 for a viewpoint and a point 42 as the location of a star which is to be in a display. The star 42 is displaced from the viewpoint by a distance X (in the X dimension), a distance Y (in the Y dimension), and a distance Z (in the Z dimension).

However, the direct path or line of sight from the point 40 to the point 42 is a distance d as indicated in the figure. It is the distance d which inversely affects the brightness of a star.

Accordingly, the intrinsic luminosity of the star is diminished in a proportion as the distance d increases.

Another correction (spherical depth cueing) stems from the fact that as a star moves radially in the display, it is manifest by light which impacts on the dome D (Figure 1) at progressively closer locations to the viewer. Consequently, there may be a tendency for the star to appear to increase in brightness. Therefore, in accordance with an aspect of the present invention, the intensity of a light beam projected to form a star is diminished somewhat with deflection from the central axis of the dome D so as to compensate for this phenomena.

The system of the present invention incorporates intensity-correction structure for developing signals indicative of the distance d (Figure 6) and the radial displacement r of a star on the dome D (Figure 1). Such signals then are used in modulating the light beam indicative of a star so as to obtain the correct brightness. The structure for performing such functions is illustrated in Figure 7 and will now be considered in detail.

The deflection signals X, Y and Z for a star are applied to a distance resolver 46 to generate absolute distance signals in a line 43.

Functionally, the resolver 46 computes values representative of the length of the line d indicated in Figure 6, utilizing a standard computation of the coordinate values X, Y and Z. In addition, the horizontal and vertical deflection signals 32 and 33 in Figure 5 are combined in the circuits 34 and 38 to produce a function-of-radial-distance signal 37. These two circuits 34 and 38 are shown for clarity in Figure 7 as the Radial Distance Resolver 47.

The signals in lines 37 and 43 are applied to an analog circuit 50 which also receives a signal B representative of the brightness of the star (derived from signal I). Of course, various arithmetic operations can be performed on the brightness signal B; however, in accordance with the embodiment disclosed herein, that value is diminished proportionately to the signals f(r) in the line 37 and d in the line 43. The signal d accounts for the increase in observed intensity with the decreased distance between the observer and the star. The signal f(r) accounts for the spherical depth distortion in intensity.The system as disclosed herein involves an arithmetic manipulation by the circuit 50 to provide the corrected intensity signal B lc= f(r)xKd The resulting signal lc constitutes the beam modulating signal which in turn determines the brilliance or light intensity of a displayed star.

From the above, it may be seen that the picture controller 10 (Figure 1) provides the elemental signals for a planetarium display with the basic display being generated to accommodate intensity correction by the circuit 39 and deflection compensation by the circuits 30 both connected to receive an input from the displacement circuits 54. Additionally, a signal indicative of star color is supplied from the processor to a color signal generator 52 which drives the color control unit C. Essentially, a color signal C is registered for each star to develop a voltage that is scaled to produce a voltage related to the desired color for the star. Such a voltage is then applied from the generator 52 (amplifier) to the color control unit C which takes the form of a PLZT electro-optic ceramic device as well known in the prior art for providing selective color filtering of light.Such devices are available from Motorola, Inc., Albuquerque, New Mexico, and have been described in a variety of publications inciuding an article "Electro-optical Ceramics" in Applied Solid State Science, Academic Press, New York 1974, pages 137-233, by Land, Thacher, and Haertling.

Fundamentally, the ceramic device passes the light from the image display and projection unit P with little attenuation; however, as the applied voltage to the device exceeds a predetermined voltage, further increases accomplish selective color filtering so as to impart the desired coloring to displayed stars.

As indicated above, the display is of a calligraphic nature with the consequence that during the very brief instant when a star is displayed, the color control unit receives an appropriate voltage to accomplish the desired color filtering and thereby attain the desired color for the star in the display. Normally, colors range from pale blue to light orange.

As another aspect of the system of the present invention, the representations of stars can be altered (either in a dynamic display or statically) to indicate changes with respect to time. For example, it may be desirable to provide a dynamic display indicating the changes in a celestial view as occurred during a period of many thousands of years. Such a display might, for example, involve a pattern of change wherein the celestial display exhibits a real time change of 5,000 years per second. In accordance herewith, the changes observed during such an interval are based upon the registered signals AX, AY, AZ, Al, and AC.

Essentially, these changes recognize incremental displacements of individual stars with respect to a reference viewpoint as well as incremental changes in the luminosity or color of the stars.

Each of the incremental signals, e.g. AX, is related to time with the consequence that a select constant may be applied to accomplish a desired incremental change. The structure for performing such operation is embodied in a specialized circuit in the picturnprn-eessor 10 which is shown in detail in Figure 8. Specifically, an exemplary circuit for the increments in displacement X is represented and similar forms of circuits are provided for the Y and Z displacement, along with circuits which may be provided to indicate changes in intensity and color and which take a similar structural form.

The signal representative of the displacement X is applied through a line 60 to an X register 62.

Somewhat similarly, the AX signal is applied through a line 64 to a AX register 66. The output from the AX register is to a multiplier 68 which also receives a signal KT indicative of a desired time constant.

In the multiplier 68, the constant KT multiplies the value of AX to accomplish a predetermined change in X which is then added to the value of X in the adder 70. The output from the adder 70 is the time-adjusted value of the displacement X for manifesting a star.

As indicated above, similar changes are accomplished for the other position coordinates and may also be applied to intensity and color.

Each of the time-adjustment elements involves a separate circuit as depicted in Figure 8. Thus, repeated incremental changes in the display elements during each frame function to accomplish a dynamic presentation compacting the change of thousands of years into a display of a few minutes' duration. Resulting displacement values are provided to the displacement circuits 54 to in turn effect the proper operation of the circuits 30 and 39.

Recapitulating to some extent, it now may be seen that the system of the present invention stores positional information along with intensity and color information on each of a variety of stars which may be individually selected or selected by picking a specific celestial sector or corridor for viewing. In one operating embodiment, the memory M incorporates a data base in excess of 6,000 stars which essentially coincides to the maximum visible to the unaided eye under excellent viewing conditions at all points on the celestial sphere.

Also as indicated above, in addition to providing static planetarium views of select portions of the celestial sphere, the system of the present invention also enables movement of the viewpoint so as to provide a display coinciding to that which would occur with a departure from earth and flight to neighboring stars. In that manner, celestial bodies can be viewed in their true three-dimensional positions. In addition to these operating aspects, the system of the present invention is also capable of providing certain special-effect displays in viewing planets during various states of position and illumination.

In that regard, views of planets are accomplished in accordance with the present invention simply by registering figure forms in the memory M which figure forms are then manipulated with respect to clipping planes (an operation well known in the prior art of computer graphics) to accomplish the desired planetary displays.

Referring to Figure 9, a plane elliptical figure 72 defined by a raster pattern is stored in the memory M (Figure 1) for manipulation by the processor 10 to be variously revolved about an axis 74. Essentially, the figure 72 consists of a series of parallel scanning lines 76 which collectively define the elliptical shape. The shape is oriented in a display so that the scanning lines 76 lie parallel to the dominant source of light for a planet being simulated. Then, the figure 72 is revolved about the axis 74 utilizing conventional computer graphics techniques and structure of the processor 10, to cause it to simulate or display figures which may approach a sphere. In that manner, planets are effectively displayed by the registration of the figure 72 in the memory M (Figure 1).

In addition to the desirability of displaying planets under various circumstances, it is also desirable to display moon phases. In accordance with the present invention, a figure is registered in the memory M which may be variously oriented in space and clipped by the picture controller and processor 10 (while in a data form) to provide a display of phases of the moon. The figure is somewhat complex and consists of a number of scanning lines 84, a definitive few of which are represented in Figure 10.

A comprehension of the figure may best be explained by reference to a pair of plane semicircles 78 and 80 which are not part of the display figure, however, the peripheral edges of these semicircles coincide to terminal ends of the scanning lines 84. Considering the pattern of the scanning lines, a line 84a extends from a point 86 at one side of the semicircle 78, to an aligned point 88 of the semicircle 80. Somewhat similarly, a line 84b extends parallel to the line 84a so that the two parallel lines 84a and 84b would coincide to diametrically-opposed lines on a cylinder terminated by the semicircles 78 and 80. However, the remaining lines 84 in the figure of Figure 10 are not parallel but depart from a cylindrical configuration as exemplified by the transverse line 84c. Specifically, the line 84c extends from a ninety degree point 90 on the semicircle 78 to an opposed ninety degree point 91 on the semicircle 80. Accordingly, when viewed from the plane of the semicircles 78 and 80 along the line of sight that is generally parallel to the diameters of the semicircles 78 and 80, the figure has somewhat of a "bow tie" configuration.

However, if the viewing angle is moved some ninety degrees (remaining in the plane of the semicircles 78 and 80), the lines 84 simply appear as a parallel array of straight lines of apparently equal length.

The depicted figure 79 is positioned and clipped to provide moon displays as indicated in Figures lOB and 10C. Such positioning and clipping will now be considered.

If the figure 79 is clipped along a plane 92, preserving the upper portion of the figure and viewing it along a line of sight coinciding somewhat to the lines 84a and 84b, it may be seen that the moon shape of Figure 1 Ob is manifest. To further orient and explain the figure, in relation to the "moon" of Figure lOB, the lines 84a and 84b appear in the "moon" as points at the tip of the moon figure 94. The line 84c develops the waist or width of the moon figure 94. Those lines (not shown) positioned between the lines described above will accomplish the complete moon figure.

With the understanding of the development of the moon figure 94 (Figure 1 OB), it may be seen that an opposed moon shape 96 (Figure 1 OC) may be developed by clipping the figure 79 along a plane 98 and viewing the remaining lower portion of the figure 79 with a line of sight substantially parallel to the lines 84a and 84b.

Again, the lines 84a and 84b are reduced to points with the line 84c having the major length of a displayed line to accomplish the desired moon shape.

From the above explanations, it may be seen that the system of the present invention may be embodied to provide celestial displays with a substantial range of variation. Specifically, both static and dynamic displays may be provided which may be varied in either time or space. Color is imparted to the display providing further dimension and realism, and dynamic displays not only afford interesting and realistic special effects but useful study and education exhibitions.

To consider a specific exemplary operation, the interactive terminal T (Figure 1) may be actuated to select a particular sector of celestial display with the consequence that the related star data is provided from the memory M to the picture controller and processor 10. The data is processed to indicate preliminary color, intensity, and deflection signals for each of the stars that are to be developed in a calligraphic display.

Pursuing the sequence of operations, it is first necessary to develop deflection signals to position the electron beam (image display and projection P) for generating the light image representative of a star. Accordingly, the digital deflection data signals from the processor 10 are supplied to the picture system 12. Such signals are sequenced then provided to the correction circuits 30 wherein certain corrections are accomplished as explained above. Finally, the corrected and sequenced deflection signals are applied to the display and projection unit P so as to specify the location of each particular star in sequence of presentation.

Somewhat similarly, the intensity correction circuits 39 receive the luminosity signals which are refined from the raw data, depending upon the various considerations indicated above, to provide actual intensity signal data to the image display and projection unit P to unblank the cathode ray beam at the proper instants to provide the desired intensity for each individual star.

In sequence with the unblanking of the beam, the color control unit C provides selective filtering to impart the desired color to the light beam projecting the star from the unit P to the dome D.

Thus, the composite display is developed by calligraphic techniques affording a realistic and effective display on the dome D.

As indicated above, the display may be dynamically altered either by varying the viewpoint for observation or by varying the time in accordance with time commands to modify the data elements in accordance with increments as explained above.

Claims (12)

Claims

1. A system for providing a planetarium display, comprising: memory means for data definitive of specific stars; input means for providing viewpoint data signals in relation to said specific stars; computer means for computing display data of at least some of said specific stars as apparent from a viewpoint indicated by said viewpoint data signals; and means for visually manifesting said display data.

2. A system according to claim 1 wherein said means for visually manifesting said data comprises a projection means suitably corrected for spherical displays and a concave spherical surface for receiving images from said projection means.

3. A system according to claim 1 wherein said computer means includes an intensity control circuit for varying the apparent brightness of specific stars in relation to the viewpoint therefor.

4. A system according to claim 1 wherein said memory means stores data on said stars representative of position and intrinsic luminosity.

5. A system according to claim 1 wherein said memory means stores data on said stars representative of position, intrinsic luminosity and color.

6. A system according to claim 4 wherein said computer means includes an intensity control circuit for varying data from said memory means on said intrinsic luminosity in accordance with the viewpoint for a star.

7. A system according to claim 5 wherein said computer means further includes means for processing data from said memory means on star color, to provide a color control signal.

8. A system according to claim 7 wherein said means for visually manifesting comprises color filter means for varying light color in accordance with said color control signal.

9. A system according to claim 8 wherein said color filter means cbmprises a PLZT ceramic device.

10. A system according to claim 1 wherein said means for visually manifesting comprises a calligraphic display means.

11. A system according to claim 1 wherein said memory means further stores at least one celestial body form for manipulation and clipping to represent planets.

12. A system according to claim 11 wherein said form comprises a moon form defining a pair of opposed semi-cylindrical forms conically tapered in one dimension.

1 3. A system substantially as hereinbefore described and as shown in the accompanying drawings.