General English

General Science

  • noun something which is not usual or typical


  • The difference between the observed and the calculated position of an astronomical body caused by the time taken for light, or other radiation, to get from it to the observer
  • The imperfect formation of an image by a telescope or other optical instrument. Varieties include chromatic aberration, the differential focussing of light of different wavelengths, spherical aberration, the imperfect focussing of light because of the use of spherical rather than parabolic lens or mirror surfaces, coma, the blurring of off-axis images, astigmatism, the distortion of images because of the irregular curvature of lenses, mirrors or the surface on which the images are formed.



  • In optics, the inability of an optical lens to produce a perfect correlation between an object and its resulting image. This can be due to various factors, including the physical properties of the lens. Types of optical aberration include curvature, astigmatism, spherical aberration, and chromatic aberration. Also called optical aberration.


  • noun an action or growth which is not usual or expected