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# Astrophysics/Regarding wind and sun

Question
QUESTION: Hi,

How are air, wind formed? Also suppose if earth had been the at center and sun revolves around earth, can such a system  exist or totally impossible?

We have air simply because when earth was formed, some 5 billion years ago, gaseous elements and compounds, such as nitrogen, oxygen, carbon dioxide, and some others were trapped by gravity. Since those elements and compounds are lighter than the elements forming the earth's core and crust, such as iron, carbon, copper, zinc, etc., those materials were largly expelled from the interior. Some, of course, remain trapped. But the expelled material formed the "air" surrounding a solid earth.

As to why we have wind, that's a little more complicated. But an excellent explanation can be found here: http://www.metoffice.gov.uk/learning/wind/what-causes-wind

The earth doesn't REALLY revolve about the sun (although it appears to) and the sun doesn't revolve about the earth. They BOTH revolve about their "center of mass", which happens to be located deep inside the sun because the sun is so much more massive (weighs more) than the earth. If you could imagine that the earth and sun had the same mass, then they would both revolve around a point in space mid-way between them. All stable orbits MUST revolve around their mutual center of mass. It's impossible to hold one body stable (fixed in space) while the other body revolves around it. Unless the second body had no mass at all. Again, impossible with a real system.

Prof. James Gort

---------- FOLLOW-UP ----------

Can we make two spheres (similar to sun and earth in relative terms) in a lab to make the smaller sphere rotate larger one purely based on gravitational force.

regards.

Hi Ameen,

No, we can't make two spheres which revolve around each other due to their mutual gravity because the gravitational force is so weak. It's the weakest of the four fundamental forces, and requires huge masses (much larger than we can make in the lab) to exert enough force that we could have a stable orbit. Even though gravity is weak for ordinary-sized masses, it can extend large distances, which is why earth is held in a stable orbit around the sun.

We can, of course, measure the gravitational force in the lab between two small masses using very sensitive instruments. But at least today, orbits in the lab influenced only by gravity between the bodies are not possible.

Prof. James Gort

Astrophysics

Volunteer

#### James Gort

##### Expertise

Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.

##### Experience

I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

Publications
StarDate, University of Texas, numerous Journal Publications

Education/Credentials
B.A. Physics and Astronomy M.Sc. Physics Ph.D. Astrophysics