使用dec/ra来计算子月球位置时的困惑 [英] Confusion with using dec/ra to compute sub-lunar location
问题描述
对于给定的日期/时间，我需要计算视在方位角和仰角以及副月球纬度/经度.我得到的az/el角度通常与其他来源(MoonCalc.org，Horizons等)一致，但是对于月下纬度/经度，没有很好的比较来源.更重要的是，我怀疑使用dec/ra值得到的经/纬度，因为ra在长时间范围内几乎没有变化.
I have a need to compute the apparent azimuth and elevation angles as well as the sub-lunar lat/lon for a given date/time. The az/el angles I get generally agree with other sources (MoonCalc.org, Horizons, etc.) but there are not good comparison sources for the sub-lunar lat/lon. More importantly, I doubt the lat/lon I get using the dec/ra values because the ra barely changes over long time frames.
这是我打的基本电话:
roc.date='2018/1/1 01:00:00'
moon=ephem.Moon(roc)
print('rocMoonTest: %s UTC-4, lat/lon = %0.4f [+N], %0.4f [+E]' %
(roc.date, math.degrees(roc.lat), math.degrees(roc.lon)))
print('Moon dec/ra = %s [+N], %s [+W]' % (moon.dec, moon.ra ))
print('Moon a_dec/a_ra = %s [+N], %s [+W]' % (moon.a_dec, moon.a_ra ))
print('Moon g_dec/g_ra = %s [+N], %s [+W]' % (moon.g_dec, moon.g_ra ))
print('Moon az/el = %0.4f, %0.4f' %
(math.degrees(moon.az), math.degrees(moon.alt)))
然后我每3个小时进行一次迭代.下面是输出:
And then I iterate on that every 3 hours. Below is the output:
rocMoonTest: 2018/1/1 01:00:00 UTC-4, lat/lon = 43.0000 [+N], -78.0000 [+E]
Moon dec/ra = 18:53:07.1 [+N], 5:43:03.33 [+W]
Moon a_dec/a_ra = 19:22:21.3 [+N], 5:39:38.43 [+W]
Moon g_dec/g_ra = 19:22:44.7 [+N], 5:40:41.41 [+W]
Moon az/el = 105.3953, 43.0670
rocMoonTest: 2018/1/1 04:00:00 UTC-4, lat/lon = 43.0000 [+N], -78.0000 [+E]
Moon dec/ra = 19:07:55.4 [+N], 5:49:00.24 [+W]
Moon a_dec/a_ra = 19:32:24.2 [+N], 5:47:42.22 [+W]
Moon g_dec/g_ra = 19:32:35.1 [+N], 5:48:45.29 [+W]
Moon az/el = 169.5907, 65.8406
rocMoonTest: 2018/1/1 07:00:00 UTC-4, lat/lon = 43.0000 [+N], -78.0000 [+E]
Moon dec/ra = 19:13:15.7 [+N], 5:54:49.89 [+W]
Moon a_dec/a_ra = 19:41:07.2 [+N], 5:55:47.50 [+W]
Moon g_dec/g_ra = 19:41:05.5 [+N], 5:56:50.65 [+W]
Moon az/el = 246.5737, 49.4664
正如预期的那样，并通过az/el角进行了验证，在此期间，随着地球旋转，月亮从东向西摆动，并达到某个高峰高度.但是，各种dec/ra值均无明显变化.在这6个小时的跨度中，我希望看到RA大约有6个小时的变化.显然，当我使用这些ra值中的任何一个来计算经度时，都会得到错误的答案.似乎dev/ra的参考框架未随地球旋转.但是，文档表明我应该期望它.
As expected and as verified by the az/el angles, the moon swings from East to West as the earth rotates and reaches a peak altitude somewhere during the period. However, none of the various dec/ra values change significantly. Over this 6 hour span, I would expect to see approximately a 6 hour change in the ra. Obviously, when I use any of these ra values to compute the longitude, I get the wrong answer. It appears the reference frame for dev/ra is not rotating with the earth. However, the docs indicate that I should expect it to.
任何人都想解释我在理解各种正确的提升变量时出了哪些问题，以及最直接的方法是计算月下纬度/经度?请注意，我宁愿避免使用将表观az/el位置旋转为大地纬度/经度的方法.
Anyone care to explain where I went wrong in my understanding of the various right ascension variables and what the most direct way is to compute the sub-lunar lat/lon? Note, I would rather avoid using an approach that rotates the apparent az/el position into geodetic lat/lon.
推荐答案
您可以通过查看以下其他链接来加强这种方法的思路:
You might reinforce your thinking in the direction of this approach by taking a look at this other link:
这给出了基本相同的解决方案，但是对于sub_solar_point来说，也来自利亚姆·肯尼迪(Liam Kennedy)(他为格林威治给出了非零纬度)，还给出了布兰登·罗德斯的回答，他将xephem库包裹在python中，给了我们pyephem ，直到最近一直在积极维护它.布兰登现在将更多精力放在他的下一个迭代上，这是一个名为skyfield的纯python库，该库使用了最新的星历表和更直观的API.
Which gives basically the same solution, but for the sub_solar_point, also from Liam Kennedy (where he gave a non zero Lat for Greenwich), and also with an answer from Brandon Rhodes who wrapped the xephem library in python to give us pyephem, and until recently was actively maintaining it. Brandon is now focusing more on his next iteration, a pure python library called skyfield, which uses the latest available ephemeris with a more intuitive API.
https://pypi.org/project/skyfield/
https://rhodesmill.org/skyfield/installation.html
尽管我现在无法提供帮助，但我是否可以建议比较一下pyephem和skyfield的结果，也许是在一两个matplotlib图中，IOW，与skyfield的结果有何不同/改进?
Although I can not contribute it now, might I suggest a comparison of the results of pyephem and skyfield, perhaps in a matplotlib figure or two, IOW, just how different/improved might be the results from skyfield?
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