February 2023 Lecture

Friday, February 10 at 7:30 pm

Live at Pace University or via Zoom

How Are Orbits Determined?

Dan Platt, PhD

IBM Watson Research Labs & Westchester Amateur Astronomers

When I was young, my family had a book on the history of astronomy. Its discussion of how Gauss determined the orbit of Ceres from the sparse measurements Piazzi had obtained fascinated me. Later, my interests in math and physics led me to celestial mechanics and methods for computing orbits, so I added to my bucket list the goal of doing an orbit calculation from scratch. Now, after many years, I decided to take the question seriously and complete these calculations. The first thing I realized is that there is a lot to it. I needed to understand coordinate systems. I will present a short history of those systems and of the precision required for these orbit methods to work. The second goal was to find how much measurement precision we need today to determine orbital elements. I wanted to see whether commercial telescopes have the precision required to permit us compute orbits. My approach was first to check my code output for known orbits from Stellarium, then to add noise to the “observed” angular measurements, and then see whether I could still compute a reasonable orbit. That will give a standard check if our commercially available scopes can deliver the required precision. As an aside, I’ll tell you just what Tycho Brahe’s fight was about that made his nose famous (and other history).