Bi-Daily Venus (BDV) is an uncommon event, occurring when an observer can view that planet twice in a single day – in the twilight of dawn and dusk. That William of Conches knew of this phenomenon in twelfth-century France is surprising given the dearth of BDV accounts. Yet following unnamed sources, he discussed BDV in three of his works: Philosophia Mundi, Glosae Super Boetium, and Dragmaticon. From the appearance of the first of these volumes (ca. 1125) to the last (ca. 1145), William’s reasoning for BDV’s occurrence changed from mild scepticism of given explanations to acceptance of Venus’s sometimes circumsolar height above the sun as the correct interpretation. This paper examines William’s evolving BDV discussions, considers what planetary height meant to William, presents an explanatory diagram, and concludes that William understood Venus to be within the ecliptic plane when BDV occurs – in contrast to our modern explanation for BDV.

中文翻译：

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海螺的威廉中世纪思想中的双日金星：用圆周太阳解释一个不寻常的天体事件

双日金星 (BDV) 是一种不常见的事件，当观察者可以在一天内两次看到那颗行星时就会发生——在黎明和黄昏的黄昏。鉴于 BDV 帐户的缺乏，Conches 的威廉在 12 世纪的法国知道这种现象令人惊讶。然而，根据未透露姓名的消息来源，他在他的三部作品中讨论了 BDV：Philosophia Mundi、Glosae Super Boetium 和 Dragmaticon。从第一卷（约 1125 年）到最后一卷（约 1145 年）的出现，威廉对 BDV 发生的推理从对给定解释的温和怀疑转变为接受金星有时在太阳上方的环绕太阳高度作为正确解释。本文考察了威廉不断发展的 BDV 讨论，考虑了行星高度对威廉的意义，并提供了一个解释图，