Author: John F. Lindner

  • We Are Going

    John F. Lindner

    After half a century confined to low-Earth orbit, and as soon as late next year, humans will once again leave Earth and voyage to Moon. The reality of this exciting adventure crystallized earlier this month when NASA announced the diverse and inspiring Artemis II crew: Clockwise from left in the photo below are Christina Koch,…

  • Behold, an Ein Stein!

    John F. Lindner

    This academic year has been thrilling: first nuclear fusion breakeven, now an ein stein! Last week, a preprint at arxiv.org by David Smith et al. announced an “ein stein”, or one stone, a shape that forces a non periodic tiling of the plane, ending a half-century quest by many researchers, including me. A retiree and…

  • Generalizing Coulomb’s Law

    John F. Lindner

    The forces between two electric charges in arbitrary motion are complicated by velocity, acceleration, and time-delay effects. The forces need not even lie along the line joining the two charges! Suppose a source charge is at position with velocity and acceleration , and a test charge is at position with velocity and acceleration . Let…

  • Triple EVA

    John F. Lindner

    Since the mid 1960s, all space walks or extra-vehicular activities (EVAs) have involved just one or two astronauts — except once. In May 1992, on the STS-49 mission, the crew of the space shuttle Endeavour was attempting to rescue a stranded communications satellite, Intelsat 603. After repeated two-person EVAs failed to capture the satellite, NASA and the…

  • 5-Color Theorem

    John F. Lindner

    On 1852 October 23, Francis Guthrie noticed that he needed only 4 colors to color the counties of England so no two bordering counties shared the same color. This works for any map, but only in 1976, and with the aid of a computer, did Kenneth Appel and Wolfgang Haken finally prove the 4-color theorem. Here I outline…

  • Compton Generator

    John F. Lindner

    Long before he won the Nobel Prize in Physics, and while still a Wooster undergraduate, Arthur Compton realized a third way to demonstrate Earth’s spin (after pendulums and gyroscopes). Compton reported his results in a manuscript submitted to the journal Science on 1913 January 13 and published as “A Laboratory Method of Demonstrating the Earth’s Rotation”,…

  • Analemma

    John F. Lindner

    Photograph the sky at the same time each day for a year and Sun will appear to execute a figure-8 path called an analemma, which is often inscribed on Earth globes and can be used as an almanac, as by Tom Hanks‘ character Chuck Nolan in the movie Cast Away. The 2D animation below illustrates…

  • Perseverance, Ignition, Breakeven

    John F. Lindner

    Overcoming decades of enormous physics and engineering challenges, and despite persistent pessimism, skepticism, and criticism, the National Ignition Facility has achieved an historic milestone for controlled nuclear fusion, a target energy gain factor of . Last week, NIF focussed the world’s most powerful laser pulse on a small gold cylinder that converted the incident ultraviolet light into x-rays and caused an enclosed…

  • Distant Retrograde Orbit

    John F. Lindner

    The Artemis 1 mission’s Orion spacecraft has successfully entered and exited a distant retrograde orbit about Moon. DRO is a stable and easily accessible orbit requiring a low velocity change . In DRO, Earth‘s non-negligible gravity contributes to a 3-body problem that makes the inertial space orbit non-Keplerian: an ellipse centered — not focussed — on Earth.…

  • Artemis Is the Sister of Apollo

    John F. Lindner

    I stayed up late last night and early this morning to watch the successful uncrewed launch of Artemis 1. In Greek tradition, Artemis was the twin sister of Apollo, and the Artemis program hopes to return humans — including the first woman — to Moon as preparation for sending them onward to Mars. As a child…

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