2024年IOAA理论第1题-日晷

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英文题目

T1. Sundial (10 points)

图一：日晷示意图

The following diagram represents a sundial, for which the triangle, called a gnomon, casts a shadow onto the surrounding surface, which has markings and numbers representing important information. It is known that this sundial is located either between the Tropic of Cancer and the Arctic Circle or between the Tropic of Capricorn and the Antarctic Circle.

Throughout the year, the shadow of the tip of the gnomon is always between curves A and C.

Read the following statements and indicate whether they are true or false. For each item, write a T on the answer sheet if you think the statement is true and an F if you think the statement is false. There is no need to explain your answers.

(a) This sundial will only function properly if it is located in the southern hemisphere. (b) Curve A represents the trajectory of the shadow of the tip of the gnomon throughout the winter solstice (in the hemisphere the sundial is located in). (c) Line B represents the trajectory of the tip of the gnomon's shadow throughout the equinoxes. (d) The solid radial lines provide the mean local solar time. (e) The analemma shape around the dashed line corresponding to 12h shows the position of the tip of the gnomon's shadow during the true solar noon at the central meridian of the time zone throughout the year.

中文翻译

T1. 日晷（10分）

图一：日晷示意图

下图表示一个日晷，其三角形部分（称为晷针）将阴影投射到带有标记和数字的周围表面。已知该日晷位于北回归线与北极圈之间或南回归线与南极圈之间。

全年中，晷针尖端的阴影始终位于曲线A和C之间。

判断以下陈述的真伪。若为真，在答题纸上写T；若为假，写F。无需解释答案。

(a) 该日晷只有在南半球才能正常工作。 (b) 曲线A代表日晷所在半球冬至日晷针尖端阴影的轨迹。 (c) 直线B代表春分或秋分日晷针尖端阴影的轨迹。 (d) 实线放射线提供平均地方太阳时。 (e) 围绕12时虚线形成的"8"字形（日行迹）显示了全年中时区中央经线真太阳正午时晷针尖端阴影的位置。

官方解答

(a) **正确**。日晷的晷针指向包含南天极的半球，因此该日晷专为南半球设计。 (b) **错误**。该曲线代表日晷所在半球夏至时晷针尖端阴影的轨迹。 (c) **正确**。这条垂直于子午线的直线代表南半球春秋分时晷针尖端阴影的轨迹。 (d) **错误**。该组放射线对应真太阳时，12时线应与南北线重合以表示真太阳正午。 (e) **正确**。虚线对应时区中央经线的真太阳时，"8"字形围绕该线显示全年平均太阳正午时阴影位置。