بسم الله الرحمن الرحيم
والصلاة والسلام على رسول الله
"محمد بن عبدالله"
وعلى آله وصحبه أجمعين
السلام عليكم ورحمة الله وبركاته
إخواني زوار وأعضاء ومشرفي المنتدى الكرام
حياكم الله وبياكم وجعل الفردوس مثواي ومثواكم
The Origin of the Solar System
The Nebular Hypothesis in its original form was proposed by Kant and Laplace in the 18th century. The initial steps are indicated in the following figures
Collapsing Clouds of Gas and Dust
A great cloud of gas and dust (called a nebula) begins to collapse because the gravitational forces that would like to collapse it overcome the forces associated with gas pressure that would like to expand it - the initial collapse might be triggered by a variety of perturbations-a supernova blast wave, density waves in spiral galaxies, etc
In the Nebular Hypothesis, a cloud of gas and dust collapsed by gravity begins to spin faster because of angular momentum conservation
It is unlikely that such a nebula would be created with no angular momentum, so it is probably initially spinning slowly. Because of conservation of angular momentum, the cloud spins faster as it contracts
The Spinning Nebula Flattens
Because of the competing forces associated with gravity, gas pressure, and rotation, the contracting nebula begins to flatten into a spinning pancake shape with a bulge at the center, as illustrated in the following figure
The collapsing, spinning nebula begins to flatten into a rotating pancake
Condensation of Protosun and Protoplanets
As the nebula collapses further, instabilities in the collapsing, rotating cloud cause local regions to begin to contract gravitationally. These local regions of condensation will become the Sun and the planets, as well as their moons and other debris in the Solar System
As the nebula collapses further, local regions begin to contract gravitationally on their own because of instabilities in the collapsing, rotating cloud
While they are still condensing, the incipient Sun and planets are called the protosun and protoplanets, respectively
Evidence for the Nebular Hypothesis
Because of the original angular momentum and subsequent evolution of the collapsing nebula, this hypothesis provides a natural explanation for some basic facts about the Solar System: the orbits of the planets lie nearly in a plane with the sun at the center (let’s neglect the slight eccentricity of the planetary orbits to simplify the discussion), the planets all revolve in the same direction, and the planets mostly rotate in the same direction with rotation axes nearly perpendicular to the orbital plane
The nebular hypothesis explains many of the basic features of the Solar System, but we still do not understand fully how all the details are accounted for by this hypothesis
وآخر دعوانا أن الحمد لله رب العالمين
وصلِّ اللهم وبارك على نبي الرحمة سيد ولد أدم أبى القاسم "محمد بن عبد الله" وعلى آله الطيبين الطاهرين وعلى أصحابه الغر الميامين وسلم تسليماً كثيراً
لا تنسونا من صالح دعائكم
رد مع اقتباس
مواقع النشر (المفضلة)