## 3-sphere

In mathematics , a 3 **sphere** is a higher-dimensional analogue of a **sphere** . It consists of the set of points equidistant from a fixed central point in 4-dimensional Euclidean space . Just as an ordinary **sphere** (or 2 **sphere** ) is a two dimensional surface that forms the boundary of a ball

**wikipedia.org**| 2011/5/1 21:17:16

## n-sphere

In mathematics , an n **sphere** is a generalization of the surface of an ordinary **sphere** to arbitrary dimension . For any natural number n , an n **sphere** of radius r is defined as the set of points in ( n + 1)-dimensional Euclidean space which are at distance r from a central point

**wikipedia.org**| 2010/9/24 22:07:41

## H-Sphere

H **Sphere** From Wikipedia, the free encyclopedia Jump to: navigation , search H **Sphere** Stable release 3.0 Patch 8 / January 8, 2008 Written in Java Operating system Linux , FreeBSD , Windows Type Control Panel (Web Hosting) License proprietary Website http

**wikipedia.org**| 2010/9/25 6:42:30

## Strömgren sphere

In theoretical astrophysics , a Strömgren **sphere** is the **sphere** of ionized hydrogen (H II) around a young star of the spectral classes O or B . Its counterpart in the real world are the H II-regions , a type of emission nebula , the most prominent of which is the Rosette Nebula . It was

**wikipedia.org**| 2011/7/5 6:25:57

## Dyson sphere

A Dyson **sphere** is a hypothetical megastructure originally described by Freeman Dyson . Such a **sphere** " would be a system of orbiting solar power satellites meant to completely encompass a star and capture most or all of its energy output. Dyson speculated that such structures would be

**wikipedia.org**| 2011/10/5 7:19:23

## Ewald's sphere

The Ewald **sphere** is a geometric construct used in electron , neutron , and X-ray crystallography which demonstrates the relationship between: the wavevector of the incident and diffracted x-ray beams, the diffraction angle for a given reflection, the reciprocal lattice of the crystal

**wikipedia.org**| 2011/8/25 11:10:38