時間：2011-04-18 00:52來源：藍天飛行翻譯 作者：航空 點擊：次
|
b. Astronomical Definitions and Background Information for Night Operations 1. Definitions (a) Horizon. Wherever one is located on or near the Earth’s surface, the Earth is perceived as essentially flat and, therefore, as a plane. If there are no visual obstructions, the apparent intersection of the sky with the Earth’s (plane) surface is the horizon, which appears as a circle centered at the observer. For rise/set computations, the observer’s eye is consid-ered to be on the surface of the Earth, so that the horizon is geometrically exactly 90 degrees from the local vertical direction. (b)Rise, Set. During the course of a day the Earth rotates once on its axis causing the phenomena of rising and setting. All celestial bodies, the Sun, Moon, stars and planets, seem to appear in the sky at the horizon to the East of any particular place, then to cross the sky and again disappear at the horizon to the West. Because the Sun and Moon appear as circular disks and not as points of light, a definition of rise or set must be very specific, because not all of either body is seen to rise or set at once. (c)Sunrise and sunset refer to the times when the upper edge of the disk of the Sun is on the horizon, considered unobstructed relative to the location of interest. Atmospheric conditions are assumed to be average, and the location is in a level region on the Earth’s surface. (d)Moonrise and moonset times are com-puted for exactly the same circumstances as for sunrise and sunset. However, moonrise and moonset may occur at any time during a 24 hour period and, consequently, it is often possible for the Moon to be seen during daylight, and to have moonless nights. It is also possible that a moonrise or moonset does not occur relative to a specific place on a given date. (e)Transit. The transit time of a celestial body refers to the instant that its center crosses an imaginary line in the sky . the observer’s meridian . running from north to south. (f)Twilight. Before sunrise and again after sunset there are intervals of time, known as “twilight,” during which there is natural light provided by the upper atmosphere, which does receive direct sunlight and reflects part of it toward the Earth’s surface. (g)Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished. 2. Title 14 of the Code of Federal Regulations applies these concepts and definitions in addressing the definition of night (Section 1.1), the requirement for aircraft lighting (Section 91.209) and pilot recency of night experience (Section 61.67). 10.2.8 Special Operations c. Information on Moon Phases and Changes in then back through partially illuminated to not the Percentage of the Moon Illuminated illuminated again. There are eight distinct, tradition-ally recognized stages, called phases. The phases From any location on the Earth, the Moon appears to designate both the degree to which the Moon is be a circular disk which, at any specific time, is illuminated and the geometric appearance of the illuminated to some degree by direct sunlight. During illuminated part. These phases of the Moon, in the each lunar orbit (a lunar month), we see the Moon’s sequence of their occurrence (starting from New appearance change from not visibly illuminated Moon), are listed in FIG 10.2.3. through partially illuminated to fully illuminated, FIG 10.2.3 Phases of the Moon New Moon . The Moon’s unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse). Waxing Crescent . The Moon appears to be partly but less than one.half illuminated by direct sunlight. The fraction of the Moon’s disk that is illuminated is increasing. First Quarter . One.half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon’s disk that is illuminated is increasing. Waxing Gibbous . The Moon appears to be more than one.half but not fully illuminated by direct sunlight. The fraction of the Moon’s disk that is illuminated is increasing. Full Moon . The Moon’s illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight. Waning Gibbous . The Moon appears to be more than one.half but not fully illuminated by direct sunlight. The fraction of the Moon’s disk that is illuminated is decreasing. Last Quarter . One.half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon’s disk that is illuminated is decreasing. Waning Crescent . The Moon appears to be partly but less than one.half illuminated by direct sunlight. The fraction of the Moon’s disk that is illuminated is decreasing. Special Operations 10.2.9 1.The percent of the Moon’s surface illumi-nated is a more refined, quantitative description of the Moon’s appearance than is the phase. Considering the Moon as a circular disk, at New Moon the percent illuminated is 0; at First and Last Quarters it is 50%; and at Full Moon it is 100%. During the crescent phases the percent illuminated is between 0 and 50% and during gibbous phases it is between 50% and 100%. 2.For practical purposes, phases of the Moon and the percent of the Moon illuminated are independent of the location on the Earth from where the Moon is observed. That is, all the phases occur at the same time regardless of the observer’s position. 3.For more detailed information, refer to the United States Naval Observatory site referenced below. d. Access to Astronomical Data for Determina-tion of Moon Rise, Moon Set, and Percentage of Lunar Disk Illuminated |
