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تسجيل

Lunar occultations

المؤلف:  James Binney and Michael Merrifield

المصدر:  GALACTIC ASTRONOMY

الجزء والصفحة:  p-84

2026-09-08

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As the Moon (or a planet) moves on the sky, it occasionally passes in front of a star and occults it. Typically, the light from a star is extinguished within a few milliseconds. To the extent that we can idealize a star as a point source and the Moon's disk as a semi-infinite plane, we expect a Fresnel diffraction pattern to sweep over the Earth as the moon passes in front of the star. This pattern can be measured by recording the brightness of the star as a function of time during the occultation. Because the star is not actually a point source but has a finite (if small) angular diameter, the diffraction pattern differs slightly from a Fresnel pattern, and, by a careful analysis of the data, one can infer the star's angular diameter (e.g., Brown 1968, Nather & McCants 1970). White & Feierman (1987) list diameters obtained in this way for 124 stars, including several fainter than V = 7 and with angular diameters ≲1 mas. The method is obviously restricted to stars near the plane of the ecliptic, and it is limited in part by imperfect knowledge of the irregularities of the Moon's limb.