In today’s example of synchronicity, I’ve been working my way (very slowly) through The Grand Design, by Stephen Hawking and Leonard Mlodinow and today I learned why the Kepler mission is named after Johannes Kepler. I guess if I was a deep reader of astronomy, I would already know about Kepler. But I’m not, so I didn’t. Until now. It’s time to rectify this gap in my (limited) knowledge of the history of astronomy. Today, the subject of my study (prior to the Feb 11th Tweetup) is Johannes Kepler. So who was this Kepler guy and why did NASA choose his name as the Mission name?
Johannes Kepler (1571AD – 1630AD) was a German mathematican, astronomer, and astrologer, back when the latter two were much more closely related than they are now. He was a key figure in the 17th-century scientific revolution that repudiated much of what people had believed since the time of Ancient Greece and provided the foundation for much of modern science. Kepler contributed two very notable ideas to this revolution of knowledge (1) the Kepler laws of planetary motion and (2) the Keplerian refracting telescope, which led to the modern refractive telescopes in use today.
There are three of Kepler laws of planetary motion. The first two were published in 1609 after he had analyzed astronomical observations of his mentor, Tycho Brahe (a Danish noble who was a noted astronomer as well). I understand Kepler’s first two laws:
1. The orbit of every planet is an ellipse with the Sun at one of the two foci.
2. A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
It took him a while to formulate the third law, and he didn’t publish it until 1619. This one I don’t really understand, being the non-math-brained person that I am:
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
(For you science lovers that want to learn more, Wikipedia has a basic explanation of Kepler’s three laws.)
Isaac Newton later used Kepler’s laws in his own theory of gravity, about a century later. Kepler’s work was that important.
The design of the Keplerian Telescope, published as Dioptrice, was an improvement on Galileo’s original design, published in 1609. Instead of using a concave lens (as Galileo had done), Kepler’s design proposed using a convex lens. This widened the field of view significantly although it did invert the image. Why was this telescope design such a breakthrough? Kepler originally felt that this design improved on Galileo’s design because it collected more light, which increased the magnification, allowing the viewer to see more detail in the small area of sky where he was pointing the telescope. It also allowed a way to insert a measuring device into the area being viewed, the first time anyone could then measure the distance between two objects over time.
The big downside of both Galileo’s and Kepler’s designs were that they required really long telescopes to overcome the abberations of the simple objective lens, along the lines of 130 to 150 feet for a lens was six inches across. Kepler never actually built a telescope using his design; he considered his design as purely theoretical. People did later build a Keplerian telescope, but it was hard to use, given the very long tube length required (the drawing above shows a 45-meter version built in 1673). Given the materials of the day used to construct the tube, it was almost impossible to keep it from bending and therefore affecting the images. (In 1668, Robert Hooke demonstrated the use of mirrors inside the tube to reflect the images and shorten the tube, a major breakthrough. A telescope formerly 60 feet long could now be shortened to 12 feet long, and that was much easier to support and stabilize.)
As part of his study of optics, Kepler wrote Astronomiae Pars Optica (The Optical Part of Astronomy) in 1604, which is generally regarded as the first description of how humans see images as inverted and reversed by the lens of our eye onto the retina.
Kepler was into a lot of things. He also explained that tides are caused by the Moon, discovered that Sun rotates about its axis, investigated the formation of pictures with a pin hole camera, and designed eyeglasses for near- and far-sightedness. (I especially appreciate that last bit, being someone who has needed vision correction since third grade!)
In one more example of synchronicity, an European unmanned resupply spacecraft is scheduled to deliver cargo to the International Space Station in February 2011. The name of that vehicle? The Johannes Kepler ATV-002 (Automated Transfer Vehicle).
It’s an amazing thing to dive into the life and work of someone I never heard about, not being the scientific type in school or in life. I’m playing catchup now, and the two hours I’ve just spent reading an introduction to Kepler’s life and work makes me realize how much I have to learn. It’s a journey, though, and today is just the second step on what I think will be a deepening of my fascination with the starry, starry night sky and the worlds we have yet to find and explore.