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The present invention relates to a lunar clock capable
of mimicking the illumination of the moon as it passes
through the phases of the lunar cycle.
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The Moon has a significant physical influence on life
on our planet due to its large size and its close proximity.
At full moon it can reflect sufficient sunlight to light up
the night. Its mass is great enough to distort the Earths
shape and to produce tides in oceans and lakes. It also
provides the main force that moves the poles of the Earth in
the precession of the equinoxes. Its shadow on the earth at
occasional times and places may obscure light from the Sun
to produce solar eclipses. Though these influences on Earth
may be subject to simple laws of physics and dynamics, we
are only just beginning to understand how the Moon may
influence the biology of life on our planet.
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The calendar month is equivalent approximately to the
period of revolution of the Moon around the Earth. This
period (29 days 12 hours 44 minutes 2.8 seconds) is the
synodic month and represents the time it takes for the Moon
to pass through the sequence of phases from new to first
quarter to full to third quarter to new again and make a
complete revolution about the Earth with respect to the Sun.
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The relative positions of the Sun, Earth and Moon
affect the illuminated lunar image that is seen by an
observer. The "New" phase occurs when the moon surface is
in full shade and all three bodies are linearly aligned with
the Moon positioned centrally. The phase "First Quarter"
occurs when the half moon surface is in sunlight forming a
semi-circular shape. This occurs as the moon revolves
around the Earth with the Sun Earth Moon angle describing an
approximate right angle. The phase "Full" occurs when the
observed surface of the moon is fully illuminated by the Sun
and again all bodies are linearly aligned but with the Earth
centrally positioned. The phase "Third or last quarter"
relates to a "half moon" but this time the moon position is
between the new moon and full moon (i.e. approximately one
hundred and eighty degrees removed from the first quarter).
The left hand side of the Moon is illuminated as observed
from Earth whereas it is the right hand side which is
illuminated at the first quarter. In between these points,
the shape of the moon appears as illuminated crescents or is
gibbous and various angles of tilt can be observed.
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Conventional moon dials (as used on various moon-phase
clocks and watches) may comprise a single disc printed with
two circular moon shapes positioned at 180 degrees to one
another rotating behind a shaped window whose shape masks
the visible or partly visible moon as it rotates to give an
impression of the lunar phase. The window shape is similar
to an axehead positioned with the crescent "cutting edge"
uppermost and semicircular convex and concave sides which
represent shadow as the moon disc rotates clockwise west to
east. A disadvantage of this mechanism is that, as the moon
goes from the third quarter to full phase, the shape of the
shadow does not accurately represent the shadow which is
observed on a near spherical object such as the Moon. As
the Moon is gibbous and approaches fullness the pattern of
the illuminated Moon produced by this mechanism is still
crescent-like whereas it is the shadow which should be
crescent shaped. Similarly, as the full Moon phase ages
further, the initial shadow effect produced by the Eastern
semicircular edge of the window is incorrect in that the
appearance of the Moon should only become crescent shaped
after the shadow covers more than half of the visible
surface of the moon.
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A moon phase dial mechanism is described in EP-A-869411.
This device mimics the lunar cycle using
overlapping, rotatable discs with appropriate shading.
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A further mechanism utilises a rotating globe, half of
which is painted white and the other half black. As this
rotates, an accurate impression of the lunar cycle is
displayed but the size of the sphere is a significant
disadvantage.
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In a further device, the various phases of the moon are
separately displayed around the circumference of a clock and
a pointer indicates the particular phase at a given time.
Since many separate moons have to be represented on the same
dial, the size of this clock is disadvantageous.
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The present invention seeks to overcome certain
disadvantages of the prior art by providing an improved
lunar clock which mimics the phases of the moon in the lunar
cycle.
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Thus viewed from one aspect the present invention
provides a lunar clock capable of mimicking the phases of
the moon in at least a part of the lunar cycle, said clock
comprising:
- a lunar image means capable of exhibiting in an
unmasked portion an image of the illuminated part of the
moon in a phase in the lunar cycle and in a masked portion
an image of the non-illuminated part of the moon at that
phase in the lunar cycle;
- masking means for partially and variably masking the
lunar image means to define the masked and unmasked portions
thereof;
- drive means for imparting relative cyclical movement to
the lunar image means and masking means through positions
which mimic each phase in the lunar cycle or a part thereof.
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The clock may mimic a part or the whole of the lunar
cycle. Preferably the clock mimics the whole lunar cycle.
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In a preferred embodiment, the lunar image means
comprises a substantially flat, disc-shaped member.
Preferably the disc-shaped member is substantially circular.
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Preferably, the lunar image means is made from
transparent material such as glass or perspex which may be
patterned. For example, patterns representing lunar craters
may be etched, sandblasted or printed on the surface of the
lunar image means.
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The masking means may take the form of a substantially
flat screen with an elongate aperture. The shape of the
aperture will be compatible with the chosen size and shape
of the lunar image means. The lunar image means may be
conveniently mounted to the rear or front of the flat
screen.
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Where the lunar image means is mounted to the rear of
the screen, the unmasked portion of the lunar image means is
visible through the aperture and the masked portion of the
lunar image means is hidden behind the surface of the screen
in order to simulate a phase in the lunar cycle.
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Alternatively, where a transparent lunar image means is
mounted to the front of the screen, light passing through
the aperture in the screen and through the lunar image means
defines the unmasked portion thereof and light prevented
from passing through the lunar image means by the screen
defines the masked portion thereof in order to simulate a
phase in the lunar cycle.
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Preferably the elongate aperture is a wave-like
aperture. In a particularly preferred embodiment, the wave-like
aperture comprises a substantially S-shaped aperture.
This would normally be used with a lunar image means in the
form of a disc-shaped member. Preferably the substantially
S-shaped aperture has rotational symmetry. Particularly
preferably, the tips of the S lie in a common, substantially
vertical plane with the middle of the S having a lateral
width which is the maximum lateral width of the aperture and
which is approximately equivalent to the diameter of the
lunar image means.
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In an alternative embodiment, the aperture of the flat
screen may take the form of approximately half of a
substantially S-shaped aperture in a horn-like
configuration. In this case, once the full moon is
simulated, the clock may be rotated through 180° by the drive
means and the direction of movement of the lunar image means
is effectively reversed. The action is repeated every half a
lunar cycle.
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In another embodiment, the masking means may take the
form of a ring so that the ends of a wavelike aperture may
be joined. This enables the lunar image means to be rotated
continuously and uni-directionally by the drive means.
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The elongate aperture may be fronted by a white, silver
or transparent material which may be back lit by a fixed
illuminating means (eg a light source). The illuminating
means may be fixed to the rear of the screen. Preferably, it
is fixed to part of the lunar image means. This
advantageously ensures that the lunar image means is
selectively illuminated as it moves relative to the masking
means. To heighten the contrast between the masked and
unmasked portions of the lunar image means, the surface of
the masking means is generally of a contrasting colour to
the lunar image means (eg black or dark blue) to simulate
the night sky.
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In order to effect relative cyclical movement of the
lunar image means and the masking means, the lunar image
means may be movably attached to the rear of the screen
whereby the drive means causes the lunar image means to
traverse the path of the aperture (eg the wave-like
aperture). Various drive means familiar to those skilled in
the art may be adopted for this purpose (eg a suitable
motor, gears and tooth belt). In general, the lunar image
means is driven by the drive means so that its movement
complements the shape of the aperture. For example, for a
wave-like aperture the movement is complementarily,
substantially wave-like. To ensure that the lunar image
means is driven by the drive means so that its movement
complements the shape of the aperture, the lunar clock may
be provided with a guiding means such as an elongate passage
or flange.
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In one embodiment, the rear of the flat screen is
fitted with two substantially parallel and substantially
vertically mounted guide rods. These may be conveniently
located outside the maximum lateral extent of the aperture,
preferably at the outer edges of the rear of the screen. A
substantially horizontal bar may be loosely coupled to the
pair of guide rods at each end by coupling means so as to
move vertically thereon and permit vertical movement of the
horizontal bar across the rear of the face of the screen.
Preferably the horizontal bar is provided with a free
sliding sleeve. The sleeve is adapted so as to be attached
to the rear of the lunar image means (eg disc). For
example, the sleeve may be provided with an integral
perpendicular rod attached to the rear of the lunar image
means. The perpendicular rod may be dependent from about
the central point of the sleeve (ie to form a substantially
T-shaped arrangement).
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The horizontal rod may be driven up and down the guide
rods by means of an appropriate drive means eg motor, gears
or tooth belt. The speed of movement is such to allow the
lunar image means to traverse positions which mimic the
phases of the moon in at least a part of the lunar cycle.
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Where the lunar image means is located at the front of
the screen, the perpendicular rod may pass through a
suitably shaped elongate passage in the screen which fulfils
the function of a guiding means. The movement imparted to
the lunar image means will therefore follow the shape of the
elongate passage. For example, for a wave-like aperture the
elongate passage may be complementarily, substantially wave-like
in shape.
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Where the masking means has an axis of symmetry, the
clock may be rotated by 180° to restart the lunar cycle.
Alternatively, the drive means may be arranged so as to
return the lunar image means to its starting position or to
drive the lunar image means in the reverse direction.
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The present invention will now be described in a non-limitative
sense with reference to the accompanying Figure
in which:
- Figure 1 illustrates a front elevation view of a
preferred embodiment of the lunar clock of the invention;
- Figure 2 illustrates a front perspective view of a
preferred embodiment of the lunar clock of the invention;
- Figure 3 illustrates a rear perspective view of a
preferred embodiment of the lunar clock of the invention.
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With reference to Figure 1, a preferred embodiment of
the lunar clock of the invention is designated generally by
reference numeral 1 in which the masking means takes the
form of a screen 2 having an elongate, wavelike aperture 3.
The lunar image means in the form of a transparent disc
shaped member 4 is driven by driving means (not shown) along
the wavelike path 5 in front of the flat screen 2.
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With reference to Figure 2, it will be seen that flat
screen 2 is dark in colour to simulate the night sky. It is
provided with an elongate passage 6 which serves to guide
the movement of the lunar image means 4 complementarily to
the wavelike, S-shaped aperture 3.
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Figure 3 illustrates in perspective view the rear of
the screen and the mode of attachment of lunar image means 4
(shown in dotted lines). The rear of the flat screen 2 is
fitted with two substantially parallel and substantially
vertically mounted guide rods 7a and 7b. A substantially
horizontal bar 8 is coupled to the guide rods 7a, 7b by
coupling means 9a, 9b in a loose manner. Appropriate
driving means (not shown) may be used to permit vertical
movement of the coupling means 9a, 9b along guide rods 7a,
7b so as to permit vertical movement of the horizontal bar 8
across the rear of the face of the screen 2. The
horizontal bar 8 is provided with a free sliding sleeve 10
which takes the form of a T-shaped arrangement which is
attached to the rear of the lunar image means 4 through the
elongate passage 6. It will be apparent that the vertical
movement of the horizontal bar 8 across the rear of the
screen permits the free sliding sleeve 10 to follow the path
of the elongate passage 6 which thereby causes the lunar
image means 4 to follow the wavelike S-shaped path of
aperture 3.
