这是天平动吗？

如图，图中黄色线圈出的两个部分的右侧，略有不同，13日图比19日图多了一些象月海一样的深色区域，这是天平动的结果吗？如果是，那么属于什么天平动，或属于哪几种天平动的综合结果，或各种天平动的贡献各是怎样的？如果不是天平动的结果，哪么是什么原因造成的。注：拍摄器材，地点相同，仅时间不同。


[ 本帖最后由 zgr0123 于 2008-5-20 17:51 编辑 ]

应该是天平动吧，经天平动。
以前还真没仔细观察过这个现象，看来还是比较明显的哈。

所谓“经天平动”是指月面在经度上出现的可见面积的变化吗？本坛子啊有专业的书籍论述之？偶想仔细研究一下下。看看自己能弄到什么深度？望bearca指点。再次感谢!

谢谢4楼jetair 。
偶打算用高一些的倍率拍摄后，做详细对比，啊有这方面的资料可供参考？

其实我对天体力学也知之甚少，不太了解现在是否有研究天平动的方向。
维基词典(http://en.wikipedia.org/wiki/Libration)上关于这个词条写了几句，有相关参考文献，还有一个很形象的动画。
不过需要挂代理上，这里把文字部分粘贴过来：

Early registration for Wikimania 2008 is now open.
Libration
From Wikipedia, the free encyclopedia
• Ten things you may not know about Wikipedia •
Jump to: navigation, search
Not to be confused with Liberation.
Simulated views of the Moon over one month, demonstrating librations in latitude and longitude.
Simulated views of the Moon over one month, demonstrating librations in latitude and longitude.

In astronomy libration (from the Latin verb libro -are "to balance, to sway", cf. libra "scales") refers to the various orbital conditions which make it possible to see more than 50% of the moon's surface over time, even though the front of the Moon is tidally locked to always face towards the earth. By extension, libration can also be used to describe the same phenomenon for other orbital bodies that are nominally locked to present the same face. As the orbital processes are repetitive, libration is manifested as a slow rocking back and forth (or up and down) of the face of the orbital body as viewed from the parent body, much like the rocking of a pair of scales about the point of balance.

In the specific case of the Moon's librations, this motion permits a terrestrial observer to see slightly differing halves of the Moon's surface at different times. This means that a total of 59% of the Moon's surface can be observed from Earth.

There are three types of libration:

    * Libration in longitude is a consequence of the Moon's orbit around Earth being somewhat eccentric, so that the Moon's rotation sometimes leads and sometimes lags its orbital position.
    * Libration in latitude is a consequence of the Moon's axis of rotation being slightly inclined to the normal to the plane of its orbit around Earth. Its origin is analogous to the way in which the seasons arise from Earth's revolution about the Sun.
    * Diurnal libration is a small daily oscillation due to the Earth's rotation, which carries an observer first to one side and then to the other side of the straight line joining Earth's center to the Moon's center, allowing the observer to look first around one side of the Moon and then around the other.

[edit] References

    * J. D. Mulhollan, E. C. Silverberg (1972). "Measurement of Physical Librations Using Laser Retroreflectors". Earth, Moon, and Planets 4: 155-159.

[edit] External links

    * APOD 11/8/99 - real photo sequence like this one
    * PixHeaven.net 04/30/07 - 24 Full Moon pictures (2 years in real time) compiled in an animation (click on the links in the page) showing the Moon's libration and variations in diameter
    * National Maritime Museum - A discussion the components of libration of the Moon with diagrams (on page 2)
    * The Antikythera Calculator (Italian and English versions)

Retrieved from "http://en.wikipedia.org/wiki/Libration"
Categories: Celestial mechanics | Orbit of the Moon

本来想把wiki上的动画也一起贴过来的，省得你去找代理了，可是有点大（2.4M），压缩也没有油水，你只好自己挂代理看了，或者给你发邮箱去。
这个动画里包含了月亮的好多运动，包括月相、月亮距离地球的距离变化等。

这个动画是电脑模拟的，如果自己搞一系列真实的观测和记录，倒也是个有趣的事情。

从原理上看，月球的天平动都不是太难理解：
经天平动是因为地球不在月亮的轨道的中心（是在椭圆的焦点上），而且月亮公转的速度不象自转速度那么均匀等原因导致的。
纬天平动是因为月球的自转轴跟公转平面并不完全垂直导致的。
周日天平动是因为观测者随着地球自转而处于不同的观测位置而导致的。

在你的照片上是危海附近，距离极区比较远，所以主要是经度方向的变化，当然也包含了其他两种天平动的影响。