Author Archives: John F. Lindner

Fifty years ago, Apollo 12 landed within sight of another spacecraft, a dramatic demonstration of pinpoint landing capability. While Dick Gordon orbited Luna in the command module Yankee Clipper, Pete Conrad and Al Bean left the lunar module Intrepid a… Continue reading →

In 1637, while reading a copy of Diophantus’s Arithmetica, Pierre de Fermat famously scribbled “Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos & generaliter nullam in infinitum ultra quadratum potestatem in d… Continue reading →

Welders in a Texas swamp have built a starship. But don’t bet against SpaceX. Starship is a prototype upper stage for a next-generation, fully reusable, two-stage-to-obit launch vehicle designed to explore and colonize Mars. Starship is made from… Continue reading →

Most people are familiar with Neil Armstrong’s iconic photograph of Buzz Aldrin during the first moon walk. Much less well-known are this pair of photographs taken just after the moon walk. To my eyes, Armstrong seems exhausted but happy; Aldrin … Continue reading →

Our TV is broken, so Aunt Nora invites us to her apartment. (Aunt Nora isn’t really our aunt, but she introduced our parents to each other, so that’s what we call her.) My brother Jim and I lie on the … Continue reading →
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Just as a vector is the sum of its components, a mechanical motion a combination of its normal mode motions, a quantum state a superposition of its eigenstates, any “nice” function is a Fourier sum of real or complex sinusoids [latex]e^{i … Continue reading →
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Today the SI (Système international d’unités) base units are redefined. The following are now exact. Memorize these numbers! Cs-133 transition frequency constant [latex]Δν_{\text{Cs}} = 9\,192\,631\,770~\text{s}^{−1}[/latex] defines the second. Then light speed constant [latex]c = 299\,792\,458~\text{m}\cdot\text{s}^{−1}[/latex] defines the meter. Then Planck’s constant [latex]h = 6.626\,070\,15\times … Continue reading →
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I set the alarm for 8:55 AM. Brutal, but I wanted to watch live the National Science Foundation Event Horizon Telescope news conference. I was expecting the first image of a black hole, and the EHT team did not disappoint. … Continue reading →
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I set the alarm for 8:55 AM. Brutal, but I wanted to watch live the National Science Foundation Event Horizon Telescope news conference. I was expecting the first image of a black hole, and the EHT team did not disappoint. … Continue reading →
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December 22 is the longest day of the year, despite being near the northern hemisphere’s shortest daylight. The sidereal day is the time to rotate 360° with respect to distant stars, about 23 hours and 56 minutes for Earth. The … Continue reading →
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