#planetary motion

(It's a trap! It's not really about pizza!) Johannes Kepler, German mathematician, astronomer and astrologer. Born into the 16th century where the geocentric model of the universe was still widely believed. Nicolaus Copernicus proposed, earlier in the century in 1543, a heliocentric universe, where earth and the other planets orbited the sun, which was believed to be near the centre of the universe. Society struggled to accept this new idea of a 'Copernican heliocentric' system as there was no more proof that this was more 'real' than the previous geocentric model. Then came Kepler.

                            On shoulders whirled in some eccentric orbit                             Just by old Paestum's temples and the perch                                    Where Time doth plume his wings.

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On shoulders whirled in some eccentric orbit

Henry David Thoreau  1817-1862

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Astronomy nerds of tumblr, I have a question. Well, a couple of questions.

1) I know some of the (dwarf) planets in our solar system (Venus, Pluto, Uranus) have retrograde rotation, but that this wasn’t the way they rotated originally and collisions/axial tilt caused the retrograde rotation. Is it theoretically possible for a planet to have retrograde rotation from the beginning of the solar system/spontaneous retrograde rotation?

2). I know Triton has retrograde orbit. Does this mean that if one was standing on the surface of Neptune, the sun would “rise” in the east and set in the west, and Triton would “rise” in the west and “set” in the east? If not, is it theoretically possible for a planet and its satellite to have a combination of orbit/rotation that would fulfill these conditions? What is it?

A Very Short Fact: German astronomer and mathematician Johannes Kepler was born on this day in 1571. He is best known for his three laws of planetary motion and for written works that would go on to inspire Isaac Newton.

“It would be more than two decades before Kepler would establish the actual pattern of the planetary speeds, but his early speculations, published in Cosmographic Mystery (1596), served notice on the astronomical community that a new talent had appeared on the scene. Kepler sent a copy to Galileo, urging him to come out in support of Copernicus, but he received only a polite response. Tycho, however, invited Kepler to join him on Hven, notwithstanding the fact that Kepler's book was the first that was irredeemably heliocentric. Kepler decided against moving to this remote island; but early in 1600, when Tycho had relocated to Prague, Kepler decided to pay him an exploratory visit, and there for three months he worked on the orbit of Mars. Except for Mercury, which is hard to track because it spends so much time lost in the glare of the Sun, Mars has the orbit that departs most from the circular and therefore is the most difficult to ‘save’ with a geometry of circles. After the three months were up, Kepler returned to Graz, but he was soon back with Tycho, who had only a short time to live. Within a year Kepler found himself Tycho's successor.”

[P.53-54: The History of Astronomy: A Very Short Introduction by Michael Hoskin]

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