- What equipment do I need?我需要什么设备？
- Almost any type of telescope will do (reflector or refractor). You will need to know the focal length of your telescope and the physical size of your CCD's pixels to calculate the pixel scale. Your setup should be such that the pixel scale is no greater than 2"/pixel (preferably) or 3"/pixel (at worst). In practice, your optimal pixel scale is something that you will have to determine for yourself, taking into consideration the capabilities of your telescope and CCD and the seeing at your site. If your pixel scale is much larger than the values quoted above, then the quality of the astrometry will suffer. If your pixel scale is too low for your local setup, then the signal-to-noise of the images may be low as each image is spread over a large number of pixels.
几乎所有类型的望远镜都可以（反射或折射等）。你必须了解望远镜的焦距以及CCD的物理像素大小以便计算像素分辨率。 按要求，你的CCD像素比例不要比2"/像素大很多，最多不超过3"/像素。事实上，考虑到望远镜、CCD及视宁度等因素，正确的像素分辨率需要实测。如果你的像素分辨率比上面要求大很多的话，那么可能导致天文测量的测量品质下降，但如果你的像素分辨率比上面要求的小很多，则会导致图片的信噪比下降，因为每个目标占据了过多的像素。
（计算像素分辨率的公式是3600*arctan(像素大小/望远镜焦距) 译者） - You will also need a computer to capture the images and software to perform the reductions. Most astrometry software packages use the Guide Star Catalogue, so a CD-ROM drive is also required. Various software packages are advertised in popular astronomy magazines:
你还需要一台计算机去捕获图片，以及相应的软件进行天文数据分类。很多天文软件包都使用引导星目录库，所以配置一个光驱也视必要的。在很多天文科普杂志上都刊登有相应软件的广告，如下一些： - Herbert Raab's Astrometrica
- An accurate clock/watch set to Coordinated Universal Time (UTC) is a must and this must be checked regularly (as a minimum, at the start of each observing session) against a [url=http://cfa-www.harvard.edu/iau/info/Astrometry.html#time]reliable standard[/url].
你的记时工具必须使用标准的世界时，而且必须经常和可靠的标准校对（至少每次观测前必须这么做）。 - Access to e-mail is also important, both for reporting observations to and receiving designations from the [url=http://cfa-www.harvard.edu/iau/mpc.html]Minor Planet Center (MPC)[/url].
E-mail也很重要，向MPC上报和收到确认都需要它。 - What sort of CCD should I use?我应该使用什么类型的CCD？It is not our place to recommend specific brands of CCDs. A look through any popular astronomy magazine shows that there are a variety of CCDs available. The CCD that is right for you depends on your computer system and on how much you want to spend.
在这里不便做任何CCD的广告，在很多天文科普杂志上都有相关广告供选择，主要依赖于你的经济实力以及你的计算机所使用的系统。 - How do I make measurements?我该如何测量？The exact details of how you will make measurements on your images and perform the reductions will depend on the software package you are using. In broad terms, you will determine pixel x,y for the centers of a number of comparison stars of known position (at least three comparison stars, preferably as many as are on the image) and the minor bodies in each image. Using these x,y measurements (determined to a fraction of a pixel) and the comparison star coordinates (taken from a suitable reference catalogue [[url=http://cfa-www.harvard.edu/iau/info/Astrometry.html#cats]see below[/url]]), the program should then do a least-squares plate-constants (LSPC) solution to derive the unknown coordinates of the minor bodies. Be suspicious of any package that does not do a proper LSPC solution!
如何准确的测量以及进行天文数据分类依赖于你所使用的软件。大体来说，你需要在每张图片中测定一些位置已知的比较星的亮度中心的像素坐标（至少三颗比较星，当然越多越好）以及小行星的像素坐标。利用这些像素坐标以及比较星的坐标（从一些合适的比较星星表[见下]获得），软件将进行一个LSPC（底片常数最小二乘法）操作来计算小行星的坐标， 很多软件做不到这一点。 You should not attempt to derive positions by overlaying charts on your images or by estimating positions by eye. The accuracy of these positions will not be sufficient.
你不该企图用目测或覆盖制图的方式估计坐标。这样不准确。
- Where should I obtain my comparison star coordinates?我该从哪里获得匹配的比较星坐标？
- Most CCD fields tend to be rather small (a few tens of arcminutes wide) and this has in the past precluded the use of traditional standard astrometric catalogues. Fortunately, the situation is now much improved.
很多CCD的拍摄视场很小（只有几十角分），在过去，这就迫使我们无法使用传统的标准天体测量星表，幸运的是，这种状况有所改观。 - A newer catalogue is the USNO-SA2.0, containing over 54 million objects (intended to be stars only, although there are some non-stellar objects), extracted from the full USNO-A2.0 catalogue, with (approximately) solar colors between 16th and 19th magnitude. USNO-SA2.0 is distributed on a single CDROM.
有一个新的星表是USNO-SA2.0，包含了5.4亿个目标恒星的数据（只包含恒星数据，虽然有很多非恒星目标），是从USNO-A2.0提取而来，包含了几乎16等到19等的恒星目标，只需要一张光碟。
- The full USNO-A2.0 catalogue, occupying ten CDROMs and containing entries for more than 526 million stars, has had a very limited distribution. Version A2.0 is also available for downloading by ftp.
完整的USNO-A2.0星表，占用10张光碟，包含超过52.6亿颗恒星，但发行量很少，该版本可以从FTP上下载。
- None of the above catalogues contain proper-motion data. It is hoped that future versions of the USNO catalogue will include this information.
以上的所有星表都不包括恒星自行的数据，我们期望以后的NSNO星表能包含这些信息。 - The following catalogues do contain proper-motion information, but generally contain far fewer entries than the catalogues listed above. The absolute accuracy of these catalogues is better than that of the USNO-(S)A catalogues.
下面罗列的星表虽然包括了恒星的自行数据，但是包含的恒星数没有USNO多，不过从精度来说，比USNO-(S)A要精确。 - The Tycho 2 catalogue contains 2.5 million entries over the whole sky.
Tycho 2星表包括了全天250万颗恒星数据。
- The ACT Reference Catalog contains entries for 988758 stars over the entire sky.
ACT Reference星表包括了全天988758颗恒星的数据。 - The UCAC 2 (second U.S.N.O. CCD Astrograph Catalog) contains positions and proper motions for 48 million stars down to R = 16, covering the sky from the south celestial pole to mid-northern declinations. UCAC 3 (the all-sky version) is expected to be released in 2005.
UCAC 2（第二USNO CCD照相星表）包括了下至16等的4.8亿颗恒星的位置和自行数据，覆盖了从南天极到北半球中赤纬地区的天空，UCAC 3（全天版本）可能会在2005年出版。 - The full USNO-B1.0 contains positional and proper motion data for more than a billion stars, occupies some 80 GB and has had a very limited distribution. The catalogue can be queried on-line.
USNO-B1.0完全版星表包括了超过十亿颗恒星的位置和自行数据，占用80GB的空间，而且发行量很少，你可以在线查询它的数据。
- Recently, versions of the some of the proper-motion-inclusive catalogues have become available from third parties in the USNO-Ax format, to allow programs that understand the USNO-Ax format to use these new catalogues without the programs requiring modification. Unfortunately, these converted versions lack the proper-motion information present in the original-format catalogues and have epochs close to the current date. It is the recommendation of the Minor Planet Center that the original-format versions be used in preference to the modified versions. If an observer insists on using the modified versions, they must be distinguished from the original version by adding ``-Ax'' to the catalogue name specified with the NET keywords. E.g., ``NET Tycho-2'' refers to the original catalogue, ``NET Tycho-2-Ax'' refers to the modified catalogue.
近来，有一些第三方的包括恒星自行数据的星表得以出版，这些星表采用USNO-Ax格式，目的是为了不更改应用USNO-Ax格式星表的软件。但不幸的是，这些更改的星表在原始格式中没有当前的自行信息，而且天文历元又很接近现在的数据。小行星中心建议最好使用原始格式。如果一些观测者坚持要求使用更改后的版本，那么你必须在NET关键字后标明“-Ax”。例如：“NET Tycho-2”表示使用Tycho-2原始版本，而“NET Tycho-2-Ax”表示使用Tycho-2的更改后的版本。 - Until quite recently, the only useable catalogue for CCD observers was the Hubble Space Telescope's Guide Star Catalogue (GSC), that contains about 18 million objects (stars and galaxies). This has a sufficient density of comparison stars for most purposes, but the positions are known to be somewhat iffy in regions that were near the edges of the plates scanned to produce the catalogue. The GSC is distributed on two CD-ROMs.
直到目前，对于CCD观测者唯一合适可用的星表是GSC（哈勃空间望远镜的引导星参考星表），它包含1.8亿个目标（恒星和星系）。参考星的密度足以满足多种观测目的，但是似乎在光碟边缘的数据读取有点问题。GSC占用两张光碟的容量。 - It is the recommendation of the Minor Planet Center that observers who are still using the GSC as their reference catalogue should migrate to the USNO-B1.0, unless their field-of-view is large enough to contain sufficient UCAC 2 stars, in which case they should use the original form of this latter catalogue.
小行星中心建议仍然使用GSC星表的观测者转为使用USNO-B1.0星表，除非你的拍摄区域足够大，才可以考虑使用UCAC 2星表用于获得足够的参考星数据。 - A new version of the GSC (version 2.2) has recently become available ( [url]http://www-gsss.stsci.edu/gsc/Copy%20of%20gsc2/GSC2home.htm[/url]). It is an all-sky catalogue containing 1 billion objects derived from digitized sky-survey plates and the catalogue is claimed to be complete to at least V = 18. Proper motions are given in this version. For the brightest objects, information has simply been copied from the Tycho-2 Catalogue. At present, only Web downloads of small areas of sky appears to be possible: there is no distribution on physical media. The final version of this GSC (version 2.3) was expected in 2003 and should contain multi-epoch proper motions for all objects.
近来，GSC的一个新版本（2.2版）已经可用（ [url]http://www-gsss.stsci.edu/gsc/Copy%20of%20gsc2/GSC2home.htm[/url]）。这是一个包含10亿颗恒星数据的全天星表，该星表基于数字巡天DSS底片，最暗星等至少到18等，而且恒星的自行数据也包含在内。对于明亮的天体，该星表拷贝了Tycho-2星表的数据。目前只能通过互联网下载到小片区域的数据：该星表还没有通过光碟等媒介出版。该星表的最终版本——2.3将可能在2003年出版并包括多个历元的所有恒星的自行数据。 - The following sources should not be used for comparison-star coordinates:
以下资源不能用于测定参考星坐标： - Certain planetarium-type software programs (generally on CD-ROM) that do not give the full-precision positions for GSC stars.
类似于天象演示的软件（往往是在光碟中），这些软件不能给出很精确的位置坐标。
- The World Coordinate System information in the FITS headers for images in the Digital Sky Survey (whether accessed via the Web or via the highly-compressed CD-ROM version).
在DSS拍摄的FITS图片文件头部分记录的世界坐标系统信息（无论是从网络中获得的或从压缩的光盘中获得的） - Any B1950.0 star catalogue (e.g., SAO Catalogue).
任何使用历元1950.0的星表（比如SAO星表）
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