|
Top Document: [sci.astro] General (Astronomy Frequently Asked Questions) (2/9) Previous Document: B.15 Is the Earth's sky blue because its atmosphere is nitrogen and oxygen? Or could other planets also have blue Next Document: B.17 Are humans affected psychologically and/or physically by lunar cycles? See reader questions & answers on this topic! - Help others by sharing your knowledge John Stockton <jrs@merlyn.demon.co.uk> The Lagrange points occur in a three-body system. Take a system consisting of a large mass M, orbited by a smaller mass m, and a third mass u, where M >> m >> u. There are five points where u can be and have the same orbital period as m. Three lie on the line connecting M and m. One (L1) lies between M and m, one (L2) lies outside the orbit of m, and one (L3) lies on the other side of M from m. Two are in the orbit of m, 60 degrees ahead (L4) and 60 degrees behind it (L5). Pictorially, we have something like this (not too scale!), with the direction of revolution indicated for m: L4 \ \ orbit of m ^ \ | L3 M L1 m L2 | / | / / L5 The Lagrangian points are often considered as places where objects, such as satellites can be "parked" for long periods. For instance, the SOHO satellite sits at the Sun-Earth L1 point in order to have a continuous, unobstructed view of the Sun, and the Wilkinson Microwave Anisotropy Probe observed from the L2 point. There is a group of asteroids, known as Trojans, which occupy the Sun-Jupiter L4 and L5 points. There are also various groups advocating human colonization of space which support putting a colony at the Earth-Moon L5 point. In fact, the L1, L2, and L3 points are "unstable equilibria." That is, an object placed there will slowly drift away if there are any other gravitational tugs on it (which there always will be due to other objects in the solar system). Thus, placing a spacecraft at the Sun-Earth L1 or L2 point requires regular "course corrections" so that it doesn't move too far from the L1 or L2 point. The L4 and L5 points are generally stable so that one should be able to remain at them indefinitely. Additional diagrams for the L points is at the WMAP site, <URL:http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html>. User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] General (Astronomy Frequently Asked Questions) (2/9) Previous Document: B.15 Is the Earth's sky blue because its atmosphere is nitrogen and oxygen? Or could other planets also have blue Next Document: B.17 Are humans affected psychologically and/or physically by lunar cycles? 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
|
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