Many years ago I was lucky enough to conduct student research at the Keck Observatories, atop the 14,000 foot peak of Mauna Kea, Hawaii. This is the site of the largest optical telescope in the world.
On one of my return flights, coincidentally I found myself sitting next to Professor Jerry Nelson, whose work was largely responsible for existence of this spectacular observatory! I asked many questions which he was willing to entertain without hesitation.
If the accomplishments of this person stopped with the design of a big telescope then that would already be commendable. In this case, though, he also managed to overcome an obstacle blocking progress to building big telescopes. The story goes something like this.
One can build larger and larger solid telescope structures only up to a certain size. Beyond a diameter of around 5 meters (or about 16 feet), the mirror approaches such a weight that it starts to sag until eventually the the ability to collect photons of light is reduced to the point that the telescope becomes unusable.
This record of a maximum diameter of 5-meters stood unchallenged for over 40 years. Then Professor Nelson had the novel approach to make instead many small mirrors and to “glue” them together electronically. His model had 36 separate 1.8 meter mirrors fitting together like puzzle pieces to act as one single mirror with a total diameter of over 10 meters.
Small mirrors are easier to manufacture, although need to be polished with high precision to have the right curvature to fit into the puzzle. Also, the electronics requirements were new and complicated. At the end of the day, the final product was a success.
It is important to note that since then others have learned how to make monolithic mirrors with apertures greater than 5 meters by reducing the weight of the support structure into a kind of 3D honeycomb structure. Both approaches work remarkably well.
Prof. Nelson’s accomplishments helped us to break the 5-m aperture barrier.
This is analogous to the story of the runner who broke the 4-minute mile that was thought for a long time to pose a barrier in terms of physical human performance. Now that the 5-m aperture barrier is broken, we are finding viable routes to build still larger telescopes to extend our reach into the universe. This is a tribute to this luminary of astronomy and also a memorial to him.
