高中地理 · 地球与宇宙

月相变化实验室

从空间关系理解现象变化

日、地、月的位置

日地、地月连线成直角，呈上弦月。

天空仍有曙暮光，月面不太显眼。

新月满月下次新月

来源说明

本教具以月相形成、日地月空间关系及地面观测为教学内容。科学概念与影像素材分别依据以下资料；图中读数由统一的理想模型计算，不接入实时星历。

一、资料依据与引用用途

月相与观测原理。 NASA Science 的 Moon Phases 用于核对月相成因、盈亏顺序、朔望周期及地球反照；Top Moon Questions 用于核对南北半球观察月面时的朝向差异。美国海军天文台的 Phases of the Moon and Percent of the Moon Illuminated 与 Rise, Set, and Twilight Definitions 分别作为月相、月面照明比例及天体升落定义的依据。

农历日期。 依据香港天文台《农历历法》，农历初一为朔所在的历日。界面中的“初几”按理想月龄标示，用于辅助理解月相顺序，不构成实际农历日期换算。

教学活动。 整体模型与地面观察相互对照的组织方式，参考太平洋天文学会（ASP）编写的 Moon Mission（2005）。该资料由 NASA Night Sky Network 收录。

二、影像来源与显示处理

地球表面。 采用 NASA Blue Marble（2002） 合成影像，包含海陆、冰雪与云层。云层为静态影像，不代表演示时刻的天气。

月球表面。 采用 NASA 科学可视化工作室 CGI Moon Kit 中的 2019 年版颜色贴图及 LOLA 起伏贴图，数据来自月球勘测轨道飞行器（LRO）。来源署名：NASA / GSFC / Arizona State University。贴图经显示亮度与凹凸强度调整，用于辨识月海、环形山和明暗边界，不用于定量测量地形或月面亮度。

星空背景。 复用“地球运动”教具中的 The Tycho Catalog Skymap（2007） 淡银河星图。制作：Tom Bridgman；来源：NASA / Goddard Space Flight Center Scientific Visualization Studio。该图依据 Tycho、Hipparcos 星表绘制，非相机照片。本页仅作固定背景，按画框裁切并调整显示亮度，不参与天体方位计算。

太阳表面的颗粒与光晕为程序绘制的外观示意。太阳光箭头表示照射方向，橙色点、圆面和虚线分别表示地面观察者、当地地平面及指向月球的视线。

三、模型假设与教学简化

几何尺度。 天体大小与相互距离未采用统一比例；地面天空中的太阳和月亮亦经放大，以保证课堂投影的辨识度。图中位置用于说明空间关系，图上长度与视直径不具有测量意义。

轨道与赤纬。 模型将地球赤道平面向外延伸作为日月运行的共同平面，即日月赤纬均固定为 0°；同时忽略轨道倾角、偏心率与季节变化。月球相对于固定日地连线匀速运动，一轮对应 29.53 天的朔望周期，不是相对于恒星公转一周。该设定用于比较月相、地方时和观察纬度的作用，不适用于演示太阳直射点移动、极昼极夜或真实月球的季节性升落变化。

变量控制。 “一日升落”固定月相，突出地球自转引起的日周运动；“一月盈亏”固定地方时，比较连续多日在同一地方时的月相与方位。现实中，地球自转与月球公转同时发生，月球在一日内的相位与相对位置也会改变。

纬度选取。 赤道、南北回归线、南北纬 45°和南北极圈分别提供赤道、低中高纬及半球对照。回归线与极圈采用教材常用值 23.5°和 66.5°；这些选项是比较用的代表纬度，不表示本模型具备相应纬线上的全部天文现象。

光照与遮影。 模型显示太阳直射形成的月面明暗，不计算日食、月食的遮影过程。“微光示意”统一增强月面暗区，服务于轮廓辨认，不模拟真实地球反照的亮度。

四、读数定义与适用范围

时间与升落。 “地方时”采用模型中的太阳时，太阳上中天为 12 时，不等同于北京时间。月出、月落以月球中心通过理想地平面为准，未计入月面半径、大气折射与地心视差。日月的实际升落星历通常以视圆面上边缘的升落为依据，并计入折射等修正，两者定义不同。

纬度与高度。 在本模型赤纬为 0°的条件下，改变纬度会改变运行高度与观察朝向，但不改变月出、上中天和月落的地方时。月亮地平高度为月球方向与当地地平面的夹角，不是距地面的垂直距离。

月面与天空投影。 月面大图在北半球采用天球北向上，南半球采用天球南向上，赤道保留北向上作对照。地面天空以当地竖直方向为参照，天顶处采用北向上示意。天空经过投影与缩放，不是相机透视图。

可见性。 页面依据月球地平高度、日月角距与天空明暗作定性判断；“位于地平线上方”不等同于“肉眼必然可见”。按天文定义，太阳中心位于地平线下 0°—18°时仍属曙暮光时段；其中 6°是民用曙暮光的界限，不能作为全部曙暮光结束的界限。页面颜色仅表示天空明暗变化，不是实际亮度测量。

日月角距小于 12°时，本页提示“通常不可见”；这一阈值仅用于区分接近新月的教学状态，不是月牙可见性的严格界限。实际观测还需考虑具体日期、地点、地物遮挡、云量及大气透明度，并查阅当地星历。

五、使用授权与第三方许可

本文件为无品牌授课版本，原有著作权和使用范围不变。第三方素材按各自许可使用。

原创内容保留原有使用范围。影像来源见第二节；字体与程序库遵循各自许可，全文列于下方。两套字体均保留完整字库，仅转换为网页压缩格式。

霞鹜文楷 · SIL Open Font License 1.1
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This Font Software is licensed under the SIL Open Font License,
Version 1.1.

This license is copied below, and is also available with a FAQ at:
http://scripts.sil.org/OFL

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SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
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PREAMBLE
The goals of the Open Font License (OFL) are to stimulate worldwide
development of collaborative font projects, to support the font
creation efforts of academic and linguistic communities, and to
provide a free and open framework in which fonts may be shared and
improved in partnership with others.

The OFL allows the licensed fonts to be used, studied, modified and
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fonts, including any derivative works, can be bundled, embedded,
redistributed and/or sold with any software provided that any reserved
names are not used by derivative works. The fonts and derivatives,
however, cannot be released under any other type of license. The
requirement for fonts to remain under this license does not apply to
any document created using the fonts or their derivatives.

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"Font Software" refers to the set of files released by the Copyright
Holder(s) under this license and clearly marked as such. This may
include source files, build scripts and documentation.

"Reserved Font Name" refers to any names specified as such after the
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月相原理与观测

月相是从地球观察到的月面受光部分的形状。判断月相，先看日地月的相对位置，再看朝向地球的月面有多少直接受光；判断能否观测，还要结合当地时刻、月球高度与天空亮度。

一、形成机制：光照与观察方向

月球自身不发可见光，明亮的月光主要来自反射的太阳光。不考虑月食、并将太阳光视为平行光时，月球有半个球面直接受光。月球绕地球公转，日地月的相对位置不断变化，从地球所见的受光部分随之改变，形成月相盈亏。

月球公转 → 日地月相对位置变化 → 所见受光部分变化 → 月相盈亏

亮面比例指所见月球圆面中，太阳直接照亮的区域所占的面积比例。它不表示月球整个表面的受光比例，也不等同于月光的明亮程度。月龄指距上一次朔经过的时间，界面以“距朔 × 天”表示。

二、相位关系：日月角距与盈亏周期

日月角距是从地球观察太阳与月球时，两者方向之间的夹角，可在整体图中用日地、地月两条连线判断。本模型中，角距从 0°增至 180°时，所见亮面由无到满；角距减小时，亮面逐渐缩小。

四个典型月相的几何关系（本模型）
月相日月相对方位角距亮面比例
新月（朔）月球与太阳同向0°0%
上弦月月球位于太阳以东90°50%
满月（望）月球与太阳反向180°100%
下弦月月球位于太阳以西90°50%

由朔至望，所见亮面逐渐扩大，称为“盈”；由望至下次朔，所见亮面逐渐缩小，称为“亏”。上弦月与下弦月的亮面比例相同，但日月相对方位不同，不能仅凭亮面比例区分月相阶段。

表中“以东”“以西”表示月球相对于太阳在天球上的方向，不是屏幕左、右，也不是月出、月落的地平方位。

相邻两次朔之间为一个朔望月，平均 29.53 天。月球相对于恒星公转一周为一个恒星月，平均 27.32 天。由于地球同时绕太阳公转，月球绕行一周后还需继续运行，才能恢复同样的日地月相对位置，因此朔望月长于恒星月。

拓展：亮面比例的计算

在本教具的平行光模型中，以 ε 表示日月角距、f 表示所见月球圆面的亮区面积比例：

f = (1 − cos ε) / 2

角距为 0°、90°、180°时，亮面比例分别为 0%、50%、100%。日常判断可先使用上表的空间关系，再用公式作定量验证。

农历初一为朔所在的历日。界面的“初八”“十五”等为教学对应，具体月相发生的农历日期与时刻随月份而变化。

三、升落规律：地球自转与日月方位

地球自西向东自转，使日月产生自东向西的日周视运动。月球相对于太阳的方向决定两者上中天的先后。上弦月位于太阳以东，比太阳晚 6 小时上中天；下弦月位于太阳以西，比太阳早 6 小时上中天。以上时差对应本模型的理想条件。

日月赤纬均为 0°时的理想地方时
月相月出上中天月落主要夜间观测时段
新月06:0012:0018:00通常不可见
上弦月12:0018:0000:00上半夜
满月18:0000:0006:00整夜
下弦月00:0006:0012:00后半夜

上述时刻对应本教具的理想条件。真实月球的赤纬不断变化，升落时刻还受日期和观察纬度等因素影响；上弦月、下弦月也可能在白昼被观察到。

四、地平坐标：观察点与纬度

地球表面的橙色点代表地面观察者，橙色圆面代表当地地平面，虚线表示指向月球的视线。地面天空图以同一观察点确定方位与高度，将整体图中的空间关系转换为当地天空中的位置。

地平高度是天体方向与当地地平面的夹角，是角度量，不是月球距地面的距离：0°位于地平线上，90°位于头顶正上方的天顶，负值表示位于地平线下。上中天指天体通过当地子午圈靠近天顶的一半；本模型中，此时月球达到当天最高位置。

本模型把日月的运行方向都放在地球赤道平面内，即赤纬为 0°。在这一条件下：

上中天高度 = 90° − |观察纬度|

在本模型中，纬度绝对值越大，月球上中天高度越低；北半球上中天方向为南方，南半球为北方，赤道上经过天顶。改变纬度会改变月球的高度与月面的朝向，不改变同一时刻的月相阶段。这些高度与方向规律不能直接套用于赤纬不断变化的真实月球。

拓展：赤纬与上中天高度

赤纬表示天体方向偏离地球赤道平面的角度，向北为正、向南为负。若观察纬度为 φ、赤纬为 δ，则上中天高度为：

上中天高度 = 90° − |φ − δ|

本模型取 δ = 0°。真实月球的赤纬随时间变化，因此相同纬度的上中天高度也会随日期变化。

五、观测条件：可见性与月面朝向

月球位于地平线上方，是直接观测的必要条件之一。能否辨认月面，还取决于日月角距、天空亮度和大气状况。新月附近，月球与太阳方向接近，朝向地球的受光部分很少，通常难以肉眼观测；月球与太阳角距较大时，白昼也可能可见。

同一时刻，南北半球所见月相阶段基本相同，但当地竖直方向不同，月面呈现的朝向可以不同。“左侧亮”或“右侧亮”需要结合观察方向判断，不能脱离视角单独定义月相。

地球反照是地球反射的太阳光照亮月面暗区的现象，在细弯月时较易辨认。本页“微光示意”用于增强暗区轮廓，不代表实际反照强度。

六、概念辨析：月相与日月食

月相变化源于观察方向变化，不是地球阴影遮住了月球。日食是月球运行到日地之间、遮住部分或全部太阳；月食是月球进入地球阴影。

日食发生于朔，月食发生于望，但并非每逢朔、望均有日月食。月球轨道平面与地球公转轨道平面（黄道面）之间有 5°左右的夹角；朔、望时月球还须位于两平面交线附近，才可能发生食现象。本页不模拟食现象的遮影过程。

本页模型的适用条件
  • 圆轨道、匀速运动，日月赤纬固定为 0°；未加入季节、轨道倾角与偏心率。
  • 月出、月落以月球中心通过地平面为准，忽略大气折射、地心视差与月面半径。
  • “一日升落”固定月相；“一月盈亏”固定地方时。天体大小与距离未按统一比例。
  • 月面明暗用于说明光照几何，不模拟食现象；暗区微光为显示增强。

原始资料、影像署名及各项简化的用途，见页面左下角“来源说明”。