为了在白天追踪时间，发明家发明了日晷，它通过太阳阴影的长度或方向来指示时间。
In order to track temporal hours during the day, inventors created sundials, which indicate time by the length or direction of the sun's shadow.
如果我只取一足够小的时间，这阴影部分就像一个三角形。
If I take a sufficiently small amount of time, this shaded part looks like a triangle.
十九世纪时，天文学家花了大量时间寻找穿过太阳的阴影。
In the 19th century astronomers spent a lot of time seeking shadows crossing the sun.
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