2009年7月22日日全蚀--3.5 在全蚀带边界的计时工作
终于把3.5翻完了，做事太拖沓:sleepy:因为没有看前面的PDF，所以一些专业词句可能是翻不准的，所以请看过的朋友多多指正。3.6的翻译随后奉上。
有空我争取把PDF前面部分看一遍~
3.5 路径极限的计时
对在本影路径的北极限和南极限附近（例如，放牧区）产生的珠状现象的精确计时，可能对在日食时利用月亮测量并计算太阳的直径是有用的。上述测量方法对于一个正在进行的侦测太阳直径变化的项目具有重要意义。
从科学角度来说，因为日食现象的显著属性和其对地理位置的强烈依赖性，我们可以使用相对简单的设备来进行有效的观察。一台口径为3到5英寸（75-125mm）的小型望远镜，一台便携式短波收音机，以及一台便携摄像机，便可以构成进行上述测量的标准装备。时间信号是通过短波电台(如北美的WWV、CHU)广播的，在世界各地可以试着搜寻5.0、10.0、15.0和20.0MHz这些样例频率以获得这些信号。然后，在摄录下日食的同时，这些时间信号必须被记录下来。这里建议那些用摄像机的人使用一种全球定位系统（GPS）的视频时间插件，比如PFD系统(http://www.pfdsystems.com)公司的KiwiOSD，这样做的目的是将详细的贝利珠事件与月亮的特征联系起来。
最安全的计时技术是观察太阳的投影，而不是对太阳圆盘的直接成像。如果没有视频摄像机，那么可以用一个录音机录下时间信号，同时录下每次事件的口头时间播报。没有经验的观察者在做上诉观察时必须非常认真、谨慎。
下面将详细介绍一下接触式计时的方法以及相应的误差估计。这些观察的时间精确度要求是±0.5秒，经纬度的精确度要求是1弧度秒（30m），海拔精确度要求为±20m（60尺）。商品级别的GPS接收器是目前最容易也是最好的、能够达到必要精度的确定某人方位的设备。同时，GPS接收器也是一个能获取精确世界时的有效设备，因为它使用每秒一个脉冲的信号来计时；许多（其他的）接收器并不用这种方法，所以使用前应该检查接收器的具体参数。通常人们使用的国家航海电子协会的（时间？）序列在时间显示上可能会有十分之几秒的误差。
观察者的大地坐标最好也要用GPS接收器记录下来。即使是最简单的手持（GPS）型号也可以使用，只要它们测得的经度、纬度、海拔的数据输出能够稳定下来，被获取并能取平均。只要满足前面所述的精度要求，方位坐标也可以通过美国地质调查所的地图或其他大型地图来测量。某些大型地图在互联网上就可以获得，比如<http://www.topozone.co>。利用网站直接确定的坐标可以作为有效的检查方式，但它们的精确度往往不能满足给日食做计时的要求。如果无法获取到一个地图或GPS接收器，那么就必须记录下观察地点的详细信息，比如要提供观察地点与最近的城镇、或居住点、或附近的地标物、或是易辨出的建筑物和十字路口的距离、方向；同时用数码相机拍下关键的用作标记的地标景物的照片也非常重要。
由国际掩星计时协会（IOTA）负责协调远征活动。若想获得可能的关于观测日食路径极限的远征活动的信息，请登录<http://www.eclipsetours.com>。若想获得关于观测设备和观测日食路径极限的方法的具体信息，请登录<http://www.eclipsetours.com/edge>。若想获得更多关于国际掩星计时协会（IOTA）和日食计时的信息，请联系：
Dr. David W. Dunham, IOTA
Johns Hopkins University/Applied Physics Lab.
MS MP3-135
11100 Johns Hopkins Rd.
Laurel, MD 20723–6099, USA
电 话: (240) 228-5609
电子邮箱: david.dunham@jhuapl.edu
网 址: http://www.lunar-occultations.com/iota
关于放牧区的观测、日食的观测和贝利珠的时间计时的报告（包括那些在全食或环食路径上、路径周围所观测的），都可以按上述地址发送给Dunham博士。 呵呵，以前陈遵妫前辈的观测队就做过这样的观测，得到很多珍贵数据。 Grazing occultation
From Wikipedia, the free encyclopedia
An occultation is an astronomical event that occurs when one celestial object is hidden by another celestial object that passes between it and the observer. A grazing occultation is a special type of lunar occultation that occurs within a mile or two of the edge of an occultation's predicted path, referred to as its northern or southern limit. Within that narrow zone, an observer may see the star intermittently disappearing and reappearing as the irregular limb of the moon moves past the star, creating what is known as a grazing occultation. From an observational and scientific standpoint, these "grazes" are the most dynamic and interesting of lunar occultations.
The accurate timing of lunar occultations is performed regularly by (mostly amateur) astronomers. If several observers with telescopes and timing equipment are positioned at intervals within this zone, they can each time the sequence of disappearances and reappearances as seen from their observing location. If the positions of the observing locations are measured, the timings can be analyzed afterwards to obtain a very accurate fix of the position of the Moon relative to the star and to determine the details of the lunar mountains and valleys seen in profile along the moon's edge.
Such observations are useful for refining knowledge of the positions and motions of stars. Also, the star's disappearances or reappearances may occur in steps, indicating a previously undiscovered close double star that cannot be resolved by direct observations.
Grazing lunar occultation
From Wikipedia, the free encyclopedia
A lunar occultation occurs when the Moon, moving along its orbital path, passes in front of a star or other celestial object, as seen by an observer (normally on the Earth). A grazing lunar occultation (also lunar grazing occultation, lunar graze, or just graze) occurs when one of the two edges of the moon parallel to its orbital path appears to just touch or graze the object as the moon goes by. When this happens, a properly positioned observer will see the grazed object disappear and reappear, possibly several times, as mountains and valleys on the edge of the moon pass in front of it.
Grazes unfold over the course of a few minutes, and depending on the lunar terrain and the observer’s position, the object may disappear and reappear just once or more than 10 times. Observers deployed just a few hundred metres apart on a line perpendicular to the graze path may make radically different observations. For example, at one location a lunar mountain may pass in front of the object, causing it to disappear and reappear, while at a different position the mountain may simply pass below the star without obscuring it.
By carefully measuring the positions of many observers and timing the disappearance and reappearance events, it is possible to construct an extremely accurate profile of the lunar terrain. Since graze paths rarely pass over established observatories, amateur astronomers have become the primary recorders of graze data. They typically use portable GPS units to determine their positions and telescope mounted video cameras to record the disappearance and reappearance events. Accurate timing is provided by recording time signals (such as WWV) on the audio channel. 关于放牧区的观测、日食的观测和贝利珠的时间计时的报告（包括那些在全食或环食路径上、路径周围所观测的），都可以按上述地址发送给Dunham博士。
flydoc 发表于 2009-5-25 02:19 PM http://www.astronomy.com.cn/bbs/images/common/back.gif国内的朋友可以发在本论坛掩星观测版，这个版的版主就是IOTA的人。
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