今日課程內容：冥王星何以被除名、Solar Nebula為什麼是扁平的（九大行星剛好位於同一平面；角動量守恆）、Bode's Law
It was noticed in the 19th century that the slow precession of Mercury’s orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets (notably by the French mathematician Le Verrier). It was hypothesized that another planet might exist in an orbit even closer to the Sun to account for this perturbation (other explanations considered included a slight oblateness of the Sun). The success of the search for Neptune based on its perturbations of the orbit of Uranus led astronomers to place great faith in this explanation, and the hypothetical planet was even named Vulcan. However, in the early 20th century, Albert Einstein’s General Theory of Relativity provided the explanation for the observed precession. The effect is very small: the Mercurian relativistic perihelion advance excess is just 42.98 arcseconds per century, therefore it requires a little over twelve million orbits for a full excess turn. Similar, but much smaller effects, operate for other planets, being 8.62 arcseconds per century for Venus, 3.84 for Earth, 1.35 for Mars, and 10.05 for 1566 Icarus
Vulcans are a humanoid species in the fictional "Star Trek" universe who hail from the planet Vulcan, and are noted for their attempt to live by reason and logic with no interference from emotion.