Theres some interesting math underlying the upcoming Triple Transit across Jupiter late Friday night, when the shadows of three of Jupiters Galilean moons will be visible as they cross in front of Jupiter. Callisto’s shadow comes on stage first at 10:11 p.m. EST, followed by Io’s at 11:35 p.m, and then Europa joins them at 1:27 a.m. and the three transit together for the next 25 minutes. Unfortunately, the forecast is for rain in the DC area, so its unlikely we can see it live. . We call these transits and not an eclipses, because the shadow of each moon just makes a black spot across the planet instead of covering it up completely. Though on the surface of Jupiter, there will be solar eclipses where the moons shadows sweep across the surface. Jupiter is close to being in opposition right now, which is much like when we have a full moon -- it is opposite the sun from us, so we see it glow the most fully and intensely. So its a great time for a transit. The video below, however is from the perspective of Jupiters most outer of its four Galilean moons. . Galileo discovered these four large primary moons. Historically, this Galileo into big, big trouble when he pointed his telescope into the sky and noted there are things that orbit things other than the Earth, undermining the view that all heavenly bodies orbited the Earth at the fixed center of the universe. He first thought they were rings, but then figured out they were four distinct moons orbiting Jupiter. . The largest of the four is Ganymede, larger than Mercury or Titan, but just slightly smaller than Mars. Then next in size are Callisto and Io, both smaller than Mercury but larger than our own Moon, and then Europa, smaller than our Moon but still much larger than little dwarf planet Pluto. Yet they are just tiny black specks when crossing in front of the humongous gas giant Jupiter. Their order from innermost to outermost is: Io, Europa, Ganymede, and Callisto. . So the nifty thing going on here is that the three most inner moons are all in sync with each other, as if they are all playing the same note, but one an octave higher and another two octaves higher. Indeed, this even has a musical name: orbital resonance. That is, Io does 2 orbits for every one orbit of Europa, and 4 orbits for every one orbit of Ganymede. Yet they are synced so that you never, ever can have all three on the same side at once, though often you will get two of them together crossing the face of Jupiter. . Enter the odd man out, Callisto. When Callisto, which isnt in orbital resonance with the other three, happens to be crossing in front of the sunny side of Jupiter while two of the three inner synced moons are transiting, you get a triple-transit, which well get on Saturday. If you miss it, the next triple-transit wont take place until March 20th, 2032. In any case, the mathematical concept of orbital resonance is a thing of wonder to math and science geeks. . In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of the bodies (i.e., their ability to alter or constrain each others orbits). In most cases, this results in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of Jupiters moons Ganymede, Europa, and Io, and the 2:3 resonance between Pluto and Neptune. . Quote from: https://princeton.edu/~achaney/tmve/wiki100k/docs/Orbital_resonance.html More info: universetoday/118147/rare-triple-transit-therell-be-3-moon-shadows-on-jupiter-on-january-24th-2015/
Posted on: Fri, 23 Jan 2015 11:26:10 +0000
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