About the project

Welcome to the page of the first Bohemian Forest (Šumava) mountains Astronomical Clock. It is located in the middle of the recreational area Hojsova Straz, part of the Zelezna Ruda district. The opening took place 17th November 2017.



It all began in May of 2014 by finding a gear from a sewing machine and then by attempting to modifying it into an escape wheel for powering a clock tower. The attempt succeeded. Soon afterwards, followed by the processes of making an anchor escapement, calculation and production of the gear wheels, shafts, turret clock’s frame, shouldering into the ball-bearings, etc. Finally, a fully operational clockwork was created , which shows the time of day on the Astronomical Clock’s face. The idea has been continued, with production of the other clockworks, in order to make the complete Astronomical Clock, which would belong to the one of the most wonderful villages of Sumava (Bohemian Forest). The clockwork was completed, composed of a 24 hour dial, rotating rings and pointers that were able to show (in addition to mean solar time) also sidereal time, date and calendar month, representation of the Sun’s motion along the signs of the zodiac, current phases of the Moon, the days left until the next full moon and, last but not least, mutual aspects of the Sun and the Moon. The next component to be made was the striking mechanism, which chimes the first eight tones of The Czech Republic’s national anthem everyday at noon, and after these tones fade away, a skeleton continues by ringing the bell twelve times. Eventually a driver was made for powering the rotating star map as well as a so-called dragon pointer, which predicts solar and lunar eclipses (not just for a given location, but for any other place worldwide). Using the same driver, there are actuated hands of two smaller dials, which show sunrise and sunset times on any given day.


Hereby, I would like to express my thanks to the district of Plzen, citizens of Hojsova Straz, my friends and all the others for help and support during this project.


Please feel free to contact me if you need any further information, either via aforementioned email or on my cell phone +420 732 445 700.


Zdenek Landa

Functions of the Astronomical Clock

Upper dial is showing common citizen time, normal, or summer one.
Combined big dial in the middle part of the clock has in the center symbol of the Earth on rotating blue circle, in it is circular cutout of the Moon, in which are depicted his phases. For Astrology geeks are displayed main aspects, in which the Moon is in relation with Sun – opposition (“dumbbell”), trigon, quadrant, sextillion and conjunction (Small circle on the border of the moon). Behind the circle of the Moon is rotating larger circle, which is holding style with the symbol of the Sun.
On his border are marked days (1 till 29 + 1/2), divided to quarters. How many days passed from the new moon is showing the symbol of conjunction on the circle of the Moon, and aspects are showing arrow on the circle of the Sun.
Behind the circle of the Sun is rotating Zodiac with twelve signs and their badges. Symbol of the Sun is getting along the year through all the zodiac signs and is showing in which sign is Sun situated now. Style of the Sun is showing also on calendar month and date. Individual days are marked by small lines on the perimeter of the circle, underneath them are data round 5 days.
Outer solid twenty-four-hours-a-day dial is on the perimeter divided by minutes (in turns yellow and blue lines) and style of the Sun on it is showing middle sun time, and so during the whole year, because Sun (for now) is successfully ignoring the garbage, the humans on Earth created in time. And so, in the period of the summer time is needed to add 1 hour.
Intermediate sun day has exactly the 24 hours, which equals to 24 hours, 3 minutes and 56.55 seconds of starring time, which is shown by the symbol of the star in between signs of Virgin and the Libra. Starring day has 23 hours, 56 minutes and 4.09 seconds. Difference in that times happens because the Earth during it’s one turn in relation to stars travels on it’s journey around the Sun approximately 2,5 million kilometers. So after one year the Earth is performing one more additional turn in comparison with stars, over the Sun. Starring and Sun time has the same value at one time of the Year – about the autumn equinox.
In the lower part of the astronomical clock is turning celestial map and Dragon’s style. Celestial map is actually turning full circle once per day, but on the astronomical clock once per year. Thanks to that it is showing in elliptical cutout (border of the skyline) actual position of the stars for the midnight of the given day. On the map are marked ecliptic, equator, galactic equator and the stars till approximately 5th star’s size. Actually it is apparent size of the star (magnitude, shortcut m) , practical brightness of the star during the observation from the earth. For example Vega in constellation of Lyra (shortcut Lyr) has m=0, for brighter stars is used the negative sign, brightest star on the sky – Sirius in constellation of the Big Dog (CMa) has m = -1.45, Spica in constellation of Virgin (Vir) has m = 1, Pole Star in constellation of Lesser Bear (UMi) has m = 2.
This implies, that smaller the star seems, the higher is the number of the magnitude. Diameter of the stars on the map equals their brightness during the observation. On the “border of the skyline” are shortcuts for the pints of the compass, in the middle of it’s lower part is the south, so on the map we are orientating as to stay face to the South and hold the map over the head.
Dragon’s style is rotating in same direction as celestial map (to the left) and is used for the prediction of eclipse. Head of the dragon is showing ascending node of the Moon, the tail descending node, and the head of the dragon is position for time 0:00 of a given day. Nodes of the Moon are two intersections of the ecliptic (orbit of the Sun) and orbit of the Moon. Circulation time of the output node is approximately 18.61 year, for which time the dragon’s style makes one more turn than Starry Sky. Eclipse of the Sun or Moon ca happen on Earth, only if the Sun, Moon and moon node are lined up.
If on the middle dial plate, the arrow close to Sun’s Style, is showing to the Full Moon, or New Moon, so to the time, which is showing the head of the dragon on the lower dial we are adding the time which is showing the Dial of the Sun, and if the times on the middle and lower 24hour’s dial plate are the same, it’s happening on the Earth (not only on exact place) to Eclipse of the Sun, if it is New Moon, or to Eclipse of the Moon, if it is Full Moon. Difference in that times can be approximately 20 minutes for complete and 45 minutes for partial eclipse of the Moon and 35 minutes for complete and 75 minutes for partial eclipse of the Sun.
In-between middle and lower dials, are on the sides small dials, which are showing times of Sunrise and Sunset on that day, again in the middle Sun’s time, so in the period of the summer time, one hour has to be added. Metal points are showing equinoxes and solstices.

Technical informations


Stepping Amant’s stepping wheel is created from the wheel of the sewing machine modified on turning machine, radii has been lightened and the wheel recessed by 20 brass pins. This are on wheel screwed, from the other side flushed into the recesses and rasped by hand to the half of it’s diameter, with tolerance of the pitch 0.02 mm. Amant’s step with small numbers of the pin was chosen because the should became stronger and withstand the higher tension with higher weight of the weights (2 has the weight of 37 kg), which is important for running machine to have higher torque to drive and control other machines. Anchor pallets are cut from tool steel and further quenched. Probably due to the pins stiffness and pallets, the step wheel has been jumping at each swing. This issue has been removed by gently fitting the flywheel onto the stepper wheel. That is turning with steeper wheel, and after his stop on the pallet is continuing in motion and is “pressing” the pin to the pallet. Pendulum is metric – second, it’s rod is from invar, cylindrical “lens” with the weight of 6kg is the middle of it’s height, supported by bellow with brass pipe, which is compensating very low thermal expansion of invar rod (inaccuracy of operation is 30 seconds per week at maximum). Gear from the lithium of Rope drum is originally from the straw cutter, teeth doubled, vessels of the lantern pinion made of tool steel. All other gears are burned out by laser from carbon steel, the teeth are doped and gathered together. Friction clutch on a minute wheel is made from clutch slats of the car and of the bicycle brake disc. On drum shaft, which is turned once per 12 hours, a sprocket is fitted with 48 teeth to the drive of the pointing machine. Drum has grooved grooves as a right-hand thread, so he wind-up (unfolds) at the same time, 2 stainless steel wires, which are drawn up and down to the roof of the tower on swinging pulleys and from there lead to weights. By this extension of the path length of weights and by inserting intermediate wheel to the machine it is possible to wind it every fortnight. The pins of all shafts are mounted in rolling ball bearings, so the friction in pins is minimal. To the outer circles of the bearings are on the on the periphery cutout three semi-circular grooves and are fixed in the frame by three screws. Lubricated are in the interval of 2-3 months by the oil with Teflon additive, by means of masts attached to the frame of the machine, which overall dimensions are 50 x 65 x 50 cm.


This machine is turning by big weight on roller chain, which is similar to the cord on the machine being pulled from the machine up to the pulley below the tower hull and from there down to the weight (6 kg) on the free pulley. Running machine, which is with Display machine connected with chain link in the ratio of 3:1, even if he has big enough gyroscopic moment, for driving the Display machine alone, however when placed in exterior, especially on winter you can not rely on it. Number of teeth of the running machine is 48, on Display one 16.On the common shaft with this wheel are two coupled gears with the same number of teeth (61), which occupy the zodiac wheel (365 teeth) and Sun (366 teeth). Thanks to the Zodiac is taking one more turn over year, than the circle with the Sun’s Style. Chain wheel on running machine’s drum with 48 teeth is turned once per 12 hours, chain wheel with 16 and chain wheels with 61 teeth are so turned once per 4 hours, wheel of the sun then once per 24 hours. Turning of the circle of the moon is solved by differential transmission. From the gear (59 teeth) on shaft of the Sun is through two coupled pinions (both 24 teeth) driven gear (57 teeth) on the shaft of Moon. Sun is so “meeting” with Moon always at approximately 29,5 days (the synodic moon), so for the time which lasts from New moon to the next New moon. On the spindle shaft mounted in ball bearings, the chain wheels are mounted on the outside, if needed it’s possible to choose stronger gearing, same as on bicycle. All gears are mounted on shafts in hubs with three hexagon socket screws, after loosening them it’s possible to perform a correction of functions. Circles of the Zodiac, Sun and Moon are from outside mounted on the own shafts, which has common axis. Hollow shaft of Zodiac is shortest, has largest diameter, in from the front mounted in a rolling ball bearing, back in sliding bearing, and both the bearings are fixated in frame of machine. In it is also inserted the hollow shaft of Sun, it’s front and middle bearing is in shaft of the Zodiac, back one in the frame, and all are sliding ones. In the shaft of the Sun is longest, full shaft of Moon, placed in 3 sliding bearings similar to the shaft of the Sun. All the bearings are lubricated same way as on running machine.


Machine is driven by weight (24 kg) hinged on the roller chain over the sprocket. On its shaft is situated other sprocket, used for driving the mechanism, which is moving with figure of the Hermit. The machine is ringing at midday, starting with 1st 8 tones of our national hymn with eight hammers on eight beating rods, then with next hammer (connected with the motion of the skeleton man) 12 beats on the bell. Main part is steel cylinder, powered by gears, on which are in 8 rows next to each other welded their thumbs, which are rising and lowering the hammers on beating rods. On the back side of the cylinder are 12 thumbs in 1 row next to each other, which are driving the hammer of the bell.Stabilization of rotation is solved by classic wind turbine. Cylinder is in position before chime secured by twin lever, on which upper end is massive brass pin, fitting into the opening in cylinder. On it’s lower end, always at 12:00 o’clock the hammer is beating, so pin is jumping out from opening in cylinder and mechanism starts moving. The hammer is lifted 2 times due to the weight required, to the half of its path before midnight, to the upper position before midday. Hammer stroke is happening through the star, the lever-controlled pin on the toothed wheel of the rope drum of the running machine, which is turning once per 12 hours. Before midday is hammer in upper position supported by second lever, which is exactly at midday lifting the pin on minutes wheel of the running machine, so the machine has been started.
After Chimes (one turn of the cylinder) brass pin is fit into the hole in cylinder again. All the bearing on this machine are sliding ones, from self lubricating brass, with possibility of additional lubrication.


Celestial map on astronomical clock has slow motion – 1 turn per year. Actually it’s turning once per fewer than 24 hours, but the purpose was, to show during the day actual position of the stars for the midnight of that day. Dragon’s style is even slower, it is performing one turn for approximately 18.61 year. Relative speed ratio is secured by differential transmission. Hollow shaft of the dragon’s style is placed in the front and back part in rolling ball bearings. It is fitted with the first wheel of the differential gear (93 teeth), connected with chain wheel, into which the roller chain with the weights (8 kg) occupies. In this shaft is rotating full shaft of Starry Sky, placed in front and middle in sliding bearings, in the back in rolling ball bearing, and a second wheel of the differential gear is mounted on it (98 teeth) together with big wheel (365 teeth) with saw teeth. Both coupled pinions (both 24 teeth)engage both wheels of the differential gear. Thanks to this gearing is dragon’s style performing during the 18,61 year one more turn than starry sky. Sky is once per 24 hours turned one tooth of a large wheel by moving the anchor, which over the lever controls the pin on the Sun’s wheel of the display machine. Position of the dragon’s style behind the circle of the Starry Sky is not usual one, but it was chosen, due to the style not covering Polar and other stars. One small 24-hour dial are visible only head and tail of the dragon. On the back end of the shaft of the starry sky is fitted sprocket. The roller chain is driven from it style of the Sunrise and from it, again by chain transmission with tension pulleys, style of the Sunset.

For images from the machines assembly visit Photo Gallery


Videa online




I thank all sponsors very much…


Contact us

  • Zdeněk Landa
    Hojsova Stráž E193 Železná Ruda
    340 22 Nýrsko
    Kontaktujte nás

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