Glossary term: 相位

Description: 在天文學中，相位是指衛星或行星相對於特定觀測者而言被部分照亮的狀態。遠處的光源通常只能照亮球體表面的一半，其餘部分仍然是黑暗的。同樣，在遙遠觀測者的視線範圍內，也只有球體表面的一半左右。相位決定了觀測者視線範圍內哪一部分表面被照亮。它隨著物體、觀察者和光源相對位置的變化而變化。

最廣為人知的例子就是月相。月球、作為觀測者的地球和作為光源的太陽的相對位置會隨著月球繞地球轉動而發生變化。因此，在這段時間裡，地球上的觀測者會看到不同的月相。在觀測者的視線中，月球表面全部被照亮的階段被稱為 "滿月"；當看不到被照亮的表面區域時，是 "新月"。兩個被照亮一半的階段分別稱為 "上弦月"或 "下弦月"。照亮區域不足一半時為 "蛾眉月"。

太陽系中的行星也會出現相位（水星和金星尤其明顯），系外行星系統也會出現。對於月球來說，即使是沒有光照的區域也並非完全黑暗：它們會反射來自地球的光線，這種現象被稱為 "地球反照光"（Earthshine），最早由達芬奇記錄下來。

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

This is an automated transliteration of the simplified Chinese translation of this term

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金星在遠距離時呈現為小而幾乎盈滿的狀態，而接近太陽時視直徑增大，逐漸變為僅有一條亮細弦狀的形態。

角度問題

Caption: 這組精美的圖像是在2019年12月17日至2020年5月25日期間，在多米尼加共和國的聖多明各拍攝的，展示了在地球上看到的金星相位。當金星和地球圍繞太陽運行時，我們觀察到金星被陽光照亮的不同半球部分，與月相類似。序列圖的下方清晰地展示了金星在較遠位置時，呈現為小而明亮的凸狀，並最終在接近太陽時達到所有行星中最大的視直徑（圖像上方），呈現為一細長的弦狀。在最後一幀中，僅有2.8%的金星表面被照亮。
Credit: 克里斯托弗·巴埃斯/國際天文學聯合會教育辦公室 (CC BY 4.0)

License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons

At the top Venus is full and appears small. As the images progress it moves to half, crescent and new, appearing larger.

Phases of Venus

Caption: This is a mesmerising series of images of Venus captured from Surgères, Charente-Maritime, France, over a period of six months in 2015. The phases appear similar to the phases we see of our own Moon and occur for similar reasons. Only half of Venus is illuminated by the Sun and, from Earth, we can sometimes only see part of that illuminated half, depending on the relative positions of the Sun, Earth and Venus. Both Mercury and Venus exhibit phases because their orbit is between the Sun and the orbit of Earth. Depending on the position of Venus relative to the Sun and Earth, Venus goes through its phases over a period of time. This sequence of images beautifully showcases the transition from the ‘gibbous’ to the slender crescents. The use of infrared filters helped to capture Venus's dense perpetual cloud cover during daylight in sharp detail, providing a glimpse into the mysterious nature of the planet’s atmosphere.
Credit: Stephane Gonzales/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons

金星和水星的軌跡

Caption: 在這張合成圖中，可以看到水星（左）和金星（右）都在向日落進發。水星和金星降落時的相位都被捕捉到了，非常漂亮。從地球上看，太陽系中並非所有行星或衛星都會出現相位。出現這種現象是因為金星和水星的軌道位於地球軌道和太陽之間，有時我們只能看到每顆行星某一部分受到光照。它們的相位與我們看到的月球相位相似。
Credit: 瑪塞拉-朱利亞-佩斯 (CC BY 4.0)

License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons

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