An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 25 Search : axis
principal axis
  آسه‌یِ فرین   
âse-ye farin (#)

Fr.: axe principal   

1) Optics: Any imaginary line passing through the center of curvature of a → spherical mirror or → lens and the corresponding geometrical center. Principal axis is perpendicular to the mirror or lens at the pole. Rays of light parallel to the principal axis of a → concave mirror will appear to converge on a point in front of the mirror somewhere between the mirror's pole and its center of curvature. Same as → optical axis.
2) Mechanics: One of three mutually perpendicular axes of an object about which the → moment of inertia is maximum or minimum. More specifically, an object has an infinite number of moments of inertia. If an object is not symmetrical about all planes through its → center of mass, then there will be one → axis of rotation about which the moment of inertia is largest, and there will be one axis of rotation about which the moment of inertia is smallest. These two axes will always be perpendicular to each other and are the principal axes of the object. The third principal axis of an object is the axis perpendicular to these two axes. In general the → angular momentum (L) of a body spinning about a point O is not in the same direction as the axis of rotation, or that of the → angular velocity angular velocity (ω); that is L is not parallel to ω. For certain bodies, however, there can be certain axes for which L and ω are parallel. In that case L = , where I is the moment of inertia about the axis in question. In a symmetric rigid body, the axes of symmetry coincide with the principal axes of the moment of inertia

principal; → axis.

radical axis
  آسه‌ی ِ پایه   
âse-ye pâyé

Fr.: axe radical   

Of two circles, the straight line containing all points P such that the lengths of the tangents from P to the two circles are equal.

radical; → axis.

rotation axis
  آسه‌ی ِ چرخش   
âse-ye carxeš

Fr.: axe de rotation   

The imaginary line around which an object rotates. Same as → rotational axis and → axis of rotation.

rotation; → axis.

rotational axis
  آسه‌ی ِ چرخش   
âse-ye carxeš

Fr.: axe de rotation   

An imaginary line about which a solid object rotates. Same as → rotation axis and → axis of rotation.

rotational; → axis.

semi-major axis
  آسه‌ی ِ نیمه‌مهین   
âse-ye nime-mehin

Fr.: demi grand axe   

Half the length of the major axis of an ellipse; a standard element used to describe an elliptical orbit. see orbital elements

semi-; → major; → axis.

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