Category Archives: Astronomy

Black Hole Radii

John F. Lindner April 10, 2019 9:42 PM

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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The Longest Day

John F. Lindner March 31, 2019 9:52 PM

December 22 is the longest day of the year, despite being near the northern hemisphere’s shortest daylight. Earth’s sidereal day is the time to rotate 360° with respect to distant stars, about 23 hours and 56 minutes, and its solar day … Continue reading →

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Luna’s Convex Orbit

John F. Lindner January 1, 2019 7:39 PM

Luna orbits Earth and Earth orbits Sol (where Luna is Earth’s moon and Sol is Earth’s star, the sun). As a kid, I thought Luna’s solar orbit formed a loopy spirograph pattern. Instead, Luna’s orbit is convex! Neglecting the eccentricity … Continue reading →

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Saturnday

John F. Lindner September 2, 2018 10:34 PM

Ancient cultures everywhere observed seven “wanderers” move against the apparently fixed stars of the night sky: our star the sun, our natural satellite the moon, and the brightest planets Mars, Mercury, Jupiter, Venus, and Saturn. In many languages, these wanderers … Continue reading →

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