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Astrophysics/Shape of earth


Why is our earth spherical like most other planets and stars? Couldn't it be flat or cubic?
I may sound a lunatic but I'm quite serious.


First, planets and stars acquire spherical shapes by different processes. Stars form from the gravitational collapse of large gas clouds (interstellar nebulae like M42 in Orion) and in the process acquire angular momentum which acts to shape the gas into a layered plasma. The spherical plasma is structured so that It is most dense at the core and less dense toward the surface.

The spherical shape, bear in mind, is the minimal volume capable of holding the maximum mass. A technical treatment entails far more than I've given here and includes consideration of the "gravitational potential" (V - - GMm/r) in terms of the central mass and gravitational attraction between it and outer layers.

Second, planets acquire their spherical shapes as angular momentum is transferred from the central massive star outwards. Thus, each originally molten world - as it rotates-  emerges as a sphere.  

The speed of the ending rotation (magnitude of angular momentum, L = mvr)  will ultimately determine how much a planet's final shape deviates from perfect sphericity. Thus, Earth is not a perfect sphere but more an oblate spheroid, sligntly less in diameter between the poles than at the equator. The same applies to Jupiter and most of the outer planets.

Of course not all astronomical bodies are spherical, for example, many of the asteroids. Check out - using Google  - the shapes of the asteroids, Gaspra and Toutatis, as well as Ceres.


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Philip A. Stahl


I specialize in stellar and solar astrophysics. Can answer questions pertaining to these areas, including: stellar structure and evolution, HR diagrams, binary systems, collapsars (black holes, neutron stars) stellar atmospheres and the spectroscopic analysis of stars as well as the magnetohydrodynamics of sunspots and solar flares. Sorry No homework problems done or research projects! I will provide hints on solutions. No nonsense questions accepted, i.e. pertaining to astrology, or 'UFOs' or overly speculative questions: 'traveling through or near black holes, worm holes, time travel etc. Absolutely NO questions based on the twaddle at this Canadian site: purporting to show a "new physics". Do not waste my time or yours by wasting bandwidith with reference to such bunkum.


Have constructed computerized stellar models; MHD research. Gave workshops in astrophysics (stellar spectroscopy, analysis) at Harry Bayley Observatory, Barbados. More than twenty years spent in solar physics research, including discovery of SID flares. Developed first ever consistent magnetic arcade model for solar flares incorporating energy dissipation and accumulation. Developed first ever loop-based solar flare model using double layers and incorporating cavity resonators. (Paper presented at Joint AGU/AAS Meeting in Baltimore, MD, May 1994)

American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.

Papers appearing in Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France). Books: 'Fundamentals of Solar Physics', 'Selected Analyses in Solar Flare Plasma Dynamics', 'Physics Notes for Advanced Level', 'Astronomy & Astrophysics: Notes, Problems and Solutions', 'Modern Physics: Notes, Problems and Solutions'

B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.

Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society. Barbados Astronomical Society award for service (1977-91) as Journal editor.

Past/Present Clients
Caribbean Examinations Council (as advisor, examiner), Barbados Astronomical Society (as Journal Editor 1977-91), Trinidad & Tobago Astronomical Society (as consultant on courses, methods of instruction, and guest speaker).

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