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Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.12 Additional planets: Next Document: E.12.2 What about a planet inside Mercury's orbit? See reader questions & answers on this topic! - Help others by sharing your knowledge contributions by Bill Owen <wmo@wansor.jpl.nasa.gov>, edited by Steve Willner <swillner@cfa.harvard.edu> Pluto was discovered from discrepancies in the orbits of Uranus and Neptune. The search was for a large body to explain the discrepancies, but Pluto was discovered instead (by accident, if you will, though Clyde Tombaugh's search was systematic and thorough). Pluto's mass is too small to cause the apparent discrepancies, so the obvious hypothesis was that there is another planet waiting to be discovered. The orbit discrepancies go away when you use the extremely accurate measurements of the masses of Uranus and Neptune made by Voyager 2 when it flew by those planets in 1986 and 1989. Uranus is now known to be 0.15% less massive and Neptune 0.51% less massive, than was previously believed. [N.B. These numbers come from comparing the post-Voyager masses to those in the 1976 IAU standard.] When the new values for these masses is factored into the equations, the outer planets are shown to be moving as expected, going all the way back to the early 1800's. The positional measurements do not bode too well for the existence of Planet X. They do not entirely rule out the existence of a Planet X, but they do indicate that it will not be a large body. Reference: Standish, E. M., Jr. 1993, "Planet X: No Dynamical Evidence in the Optical Observations," Astronomical Journal, vol. 105, p. 2000--2006 User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.12 Additional planets: Next Document: E.12.2 What about a planet inside Mercury's orbit? Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
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with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP