It is shown how erroneous results can occur using some period-finding methods, such as Fourier analysis, on data containing closely spaced frequencies. The frequency spacing accurately resolvable with data of length T is increased from the standard value of about lIT quoted in the literature to approximately 1.5/T.
If the limb of the Moon can be regarded as a straight edge, then the diffraction pattern of a point source which it produces at the distance of the Earth is the well known Fresnel diffraction pattern. Observations of stellar occultations reveal the variation of intensity with time as the diffraction pattern passes across the detector due to the orbital motion of the Moon and the rotation of the Earth. The linear scale of the diffraction pattern in monochromatic light depends on both the wavelength of observation, λ, and on the distance of the Moon, D, so that the scale is proportional to (λD)1/2.
A method for the high resolution spectroscopy of rotating planets is discussed which in principle (1) uses all the light from the planet, (2) is not limited in its resolution by the rotation of the planet, (3) can produce spectra in which the only sharp lines present must be of planetary origin, (4) retains spatial resolution in latitude, and (5) uses only conventional coudé spectrograph equipment. Although it is not possible to take full advantage of all these gains with presently available gratings, a significant improvement over present techniques is still possible.
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