While Adam is galavanting in Europe, “Physics Commando” Barry Panas joins the crew to school us on the physics of superheroes. Pat discovers who showed up in class with a game of Name That: High School Quiz Edition. Finally, Darren investigates whether there’s any truth to a claim making the rounds on the internet about a rare green moon.
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The Physics of Superheroes
Feynman on the Beauty of a Flower
Iron Man hit by Thor’s Hammer in The Avengers
Green Moon
Hey guys,
Last week, my girlfriend and I were listening to this podcast, and we agreed that the tie-breaker question was easy and that everyone should have gotten it right… except that we chose different answers. I said Mercury, and she said Venus. I just assumed I had remembered something incorrectly until I saw, today, a piece of a documentary on Mercury that mentioned that it’s tidally locked to the sun and has the longest days in the solar system.
I did some research, and it comes down to how you define a day (synodic vs sidereal). A day-night cycle on Mercury lasts much longer than the time it takes to rotate 360 degrees, because its orbit is so fast by comparison. By the time Mercury has rotated 360 degrees, it has moved more than halfway around on its orbit, so the rotation has to catch up. Sunrise-to-sunrise time on Mercury is 176 days, about twice the length of its year.
By contrast, Venus is rotating retrograde, so it has the opposite effect. Venus’s sunrise-to-sunrise time (117 days) is actually much *shorter* than its sidereal day (243 days). Since Venus has a 224-day year, its days are shorter by this metric.
Basically, if you were standing on Venus and Mercury and timed the length of the day (sunrise to sunrise) on each, you’d find that only Mercury’s day is longer than its year.
Maybe a podcast isn’t the best format for this sort of discussion, but it might make an interesting follow-up. Thanks for being awesome!
To clarify: “one rotation,” as used by Pat to define a day, could either refer to 360 degrees or a return to the same configuration.