Kepler

German astronomer and mathematician Johannes Kepler was born prematurely in 1571. He lived with his mother, an herbalist, at his grandfather's inn where he often entertained and impressed visitors with his amazing skills in mathematics. Sundials were common in many places during Kepler's youth – and so were celestial phenomena.

When he was six, his mother took him to view the Great Comet of 1577; at the age of eight, he witnessed a lunar eclipse. This early exposure to astronomy helped cultivate an active interest in the stars and eventually led Kepler to the first accurate explanation of planetary motion. He worked with giants, like Tycho Brahe and studied the works of his scientific predecessors, such as Ptolemy and Copernicus.

Kepler's Work

Kepler published a number of significant works on astronomy, optics and mathematics – three related fields in which he truly excelled. In tomes such as Astronomia Pars Optica, Dioptrice and Stereometrica Doliorum, Kepler outlined everything from the inner workings of the eye, how a telescope works and the basis of integral calculus. He coined the term satellite, worked out that the moon causes tides and, most importantly, came up with three laws that serve as the foundation for celestial mechanics today.

Kepler's first law is that the planets move around the sun in ellipses. The second law is that objects in elliptical orbits don't move at uniform rates. And Kepler's third law, which lead to Newton's law of gravitation, is that the squares of periodic times are to each other as the cubes of the mean distances.

Sundial Developments

Though there's little evidence that Kepler himself spent time developing sundials, his laws and other findings certainly had an impact on how sundials were used and developed during his lifetime and beyond. Kepler's key contribution to sundial theory was his discovery that the earth has an elliptical orbit.

This fact is particularly handy when constructing an analemmatic sundial, where the shadow-casting object – or gnomon – moves depending on the time of year. Similarly, Kepler’s laws and formulas were a key in making smaller, more functional devices for timekeeping on-the-go, such as the diptych sundial. It’s largely thanks to Kepler that one can look at a sundial in any given setting, read a handy Equation of Time plate and know exactly what the real time is.

A related object Kepler did develop with his own two hands is the platonic solid model of the Solar System. The three-dimensional model serves as a geometric idealisation of the universe, provided a physical illustration of the six known planets circling the sun, and given the data available at the time, it was staggeringly accurate. Kepler discarded the idea as it wasn’t as accurate as he thought it could be.