galactic orbit
31Formation and evolution of the Solar System — Artist s conception of a protoplanetary disk The formation and evolution of the Solar System is estimated to have begun 4.568 billion years ago with the gravitational collapse of a small part of a giant molecular cloud …
32astronomy — /euh stron euh mee/, n. the science that deals with the material universe beyond the earth s atmosphere. [1175 1225; ME astronomie ( < AF) < L astronomia < Gk. See ASTRO , NOMY] * * * I Science dealing with the origin, evolution, composition,… …
33Sun — This article is about the star. For other uses, see Sun (disambiguation). The Sun …
34Oort cloud — An artist s rendering of the Oort cloud and the Kuiper belt (inset). Sizes of individual objects have been exaggerated for visibility …
35Milky Way Galaxy — Large spiral galaxy (roughly 150,000 light years in diameter) that contains Earth s solar system. It includes the multitude of stars whose light is seen as the Milky Way, the irregular luminous band that encircles the sky defining the plane of… …
36star — starless, adj. /stahr/, n., adj., v., starred, starring. n. 1. any of the heavenly bodies, except the moon, appearing as fixed luminous points in the sky at night. 2. Astron. any of the large, self luminous, heavenly bodies, as the sun, Polaris,… …
37Places in The Hitchhiker's Guide to the Galaxy — Hitchhiker s portal This is a list of places featured in Douglas Adams s science fiction series, The Hitchhiker s Guide to the Galaxy. The series is set in a fictionalised version of the Milky Way galaxy and thus, while most locations are pure… …
38Oort constants — The Oort constants (discovered by Jan Oort) A and B are empirically derived parameters that characterize the local rotational properties of our galaxy, the Milky Way, in the following manner: where V0 and R0 are the rotational velocity and… …
39List of astronomy acronyms — This is a compilation of acronyms commonly used in astronomy. Most of the acronyms are drawn from professional astronomy and are used quite frequently in scientific publications. However, a few of these acronyms are frequently used by the general …
40Private spaceflight — This article is about non governmental spaceflight. For paying space tourists, see Space tourism. For general commercial use of space, see Commercialization of space. Astronaut Dale A. Gardner holding a For Sale sign Private spaceflight is flight …
