UGears Mechanical Tellurion model kit

The Ugears Mechanical Tellurion can be manually adjusted or "tuned" to provide an accurate depiction of the relative positions of the sun, earth, and moon on any given day. When "tuning" the mechanism, set the pointer to the middle of winter or summer on the seasons dial. The earth, on its tilted axis, can be rotated (using a gear under the phases of the moon) to have either hemisphere be farthest from the sun in the bleak midwinter, or closest to the sun in summer. Turn the handle the correct number of days forward or back, from whichever solstice is closest in time, to set the present day. After consulting a lunar calendar, use the upper gear disk to adjust the position of the moon to its correct phase. Your Tellurion is now "set." With each passing day, give the model one turn of the crank to chart the earth's progress around the sun, and the moon's lunar cycle as it orbits the earth.

As you study the movements of your Ugears model Tellurion, you will learn that the full moon occurs when the moon is behind the earth, away from the sun. This is because the sun illuminates the entire surface of the moon that is visible to us (the "bright side" of the moon). In contrast, when the moon is between the earth and the sun, the sun's rays illuminate that part of the moon that is turned away from us (the "dark side" of the moon). We call this phase the "new moon," the period when the moon is not visible in the night sky. In the intervals between these phases, the moon waxes and wanes, changing its apparent shape, depending on how much of the illuminated part we can observe from the earth. The phases of the moon are just one of many somewhat counterintuitive astronomic understandings that are easy to visualize with the Ugears Tellurion 3D puzzle.

At Ugears, a rough approximation or "close enough," isn't really our style. In representing the orbital periods of our planet and the moon, our design engineers have given the Mechanical Tellurion a sophisticated gear system (first worked out by Dutch mathematician Christiaan Huygens in the 17th C) to have the most accurate approximations possible in a wooden mechanism at this scale. The earth gearing has a 365.256 day orbital period, while the moon-earth gear system has an orbital period of 27.323, giving accuracies within one thousandth of a day.

Age 14+

Number of components: 249

Estimated time of assembly: 5 hours

Level: Medium

Age 3+, 4+, 5+, 6+