Tellurion

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A tellurion is a device that depicts how day, night, and the seasons are caused by the rotation and orientation of earth on its axis and its orbit around the sun. The device normally also displays the lunar phase. It is related to the orrery, which illustrates the relative positions and motions of the planets and moons in the solar system in a heliocentric model. This Lego Technic tellurion simulates seasons, solstices and equinoxes as well as solar and lunar eclipses. The modeled lunar configuration will be present in 2025:



It has the following features:
I.                   LED lamp for simulating the sunlight
II.                 Large motor in combination with a four-speed gearbox for covering daily,monthly, seasonal and annual effects
III.               A crank for manual visualization of daily effects and increased attraction on kids with the gearbox in neutral.
 
The following parameters are covered:
1.     360 days per year (reality 365.25)
2.      Orbit of the moon around earth in 27.8 days (reality 27.3 days)
3.      Time between full moons about 30 days (reality 29.5 days)
4.      one moon rotation per month (reality 1 rotation)
5.      Tilted earth axis of 22.5° (reality 23.4°) 
6.      Ratio of earth to moon diameter of 2.3 (reality 3.7)
7.      Distance moon to earth is 3 earth diameters (reality 30!)
8.      Angle of 11°between moons and earths orbital planes (reality 5.1°)
9.      Two time windows for solar and lunar eclipses per year (reality 2)
10. Eccentricity of earth’s orbit around the sun of 0.7 (reality 0.017).
 


The following effects are modeled:
a)     Night and day change
b)      Seasonal changes
c)      Varying distance to the sun
d)      Occurrence and absence of solar and lunar eclipses
e)      Annual absence of sunrise and sunset in the polar regions
f)      Monthly absence of moon-rise and moon-set in the polar regions
 
Let me give you some further background on this MOC. The whole thing started with the
inspirational Orrery by JKBrickworks that we built over Christmas. It is a very beautiful model with perfect instructions. Most fascinating for me was the huge attraction it had on kids. They were constantly turning the crank and discussing the various aspects of the model. I decided to expand it to a tellurion combined with LED lamps that took the tilt of the earth axis as well as the varying distance between earth and the sun during the year into account. This should expand the educational value by illustrating day and night, explaining seasons as well as lunar phases based on actual light and shadow rather than a theoretical discussion of the function of the sun. I learned that Sidebook  must have reached the same conclusions when he expanded the orrery of JKBrickworks to an impressive tellurion. Kareo understood the relevance of a light source that he added to the MOC of Sidebook. 
All these models have, however, one major shortcoming: They monthly produce lunar and solar eclipses on several consecutive days. This is well noticed by kids and you will not get away with a simple excuse. Consequently, I wanted to improve this aspect and ended up learning more about moon and earth than I really intended to:
 
I first assumed that the effect of monthly eclipses is due to the small distance between sun, earth and moon. Indeed, getting closer to the real aspect ratios decreased the problem of eclipses on several consecutive days (note that this MOC is still off by a factor of 10). But they still occurred every month. This could in principle be resolved by shifting the plane described by the orbit of the moon around earth parallel to the plane described by the orbit of earth around the sun. This eliminates any eclipse very effectively. Forever!
It turns out that these planes are not shifted parallel but tilted by 5.1°. Consequently, solar and lunar eclipse is only possible when these planes intercept, which happens twice a year. If this coincides with full or new moon these three objects (sun-moon-earth or sun-earth-moon respectively) are aligned in space and an eclipse is observed. Hence, I tilted the plane described by moons orbit in my model. This indeed eliminates most of the monthly eclipses. They are still too frequent as a result of the too small distance between moon and earth. Nevertheless, the physical effect can be illustrated. The issues, however, did not stop here. Tilting the planes in the model rose the question with respect to the relative orientation of these axes in space. I quickly learned from Wikipedia that the precession of the moons orbital axes rotates with a period of 18.6 years. I decided to build the easiest configuration that corresponds to the special case
of the so called "major lunar standstill". This configuration will be given in 2025. In this case eclipses are most probable at equinox in March or September.
Now a few words on a last issue: this model mimics the variation in distance between earth and sun. But the configuration shown here will only be true in about 12000 years. If you want to illustrate the present configuration you will have to flip earth upside down, have the south pole facing upward and run the motor backwards. In this configuration earth will be closest to the sun in the northern winter. Indeed, this case is presently given on 3rd of January. The southern summer hence receives 7.6% more solar energy than the one on the northern hemisphere.
 
 
Some construction hints:
- YES! earth is made of Lego pieces that are decorated with a sticker to make them look like
earth. Connecting the two half spheres requires this rubber tyre.
- You will need the special mould version of these two gears that can be interlocked.
- The connecting piece bringing the rotation from the base to the arm is in the lxf file not in the correct position. Make your you connect the two axles with this element
- The LED lamps are not drawn in the lxf file since they are not available. Refer to the photos for correct installation.
- There is quite some play in the model that is eliminated be the load applied by the
rubber band.
- If you do not have this older mould version, you can add this driving ring to connect the gears.There is enough room but locking the play will be difficult. The MOC will still
work, but not as smoothly.
 
Acknowledgement:
- Thanks to JKBrickworks for the inspirational orrery.
- Thanks to Sariel for the compact and rigid gearbox.
- Thanks to Princy for preparing and applying the earth sticker onto the Lego sphere.
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MOC-21357

Name Tellurion
Designer kueden
Designed 2019
Inventory 663
Theme Technic > Model
Star Wars™ Imperial Star Destroyer™
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