During his 1869 expedition down the Green River and through the Grand Canyon, Major John Powell made astronomical observations using a sextant and artificial horizon to fix the locations of key points along the rivers that were only poorly known at the time. Latitude was obtained from the altitude of Polaris or meridian transits of stars or Saturn. Local mean time was determined from equal altitude observations of the Sun. The swamping of one of the expedition's small boats ruined the chronometers, meaning that they could not be used to keep Greenwich mean time and hence find longitude. As a substitute a series of lunar distance observations were undertaken. In this paper observations recorded in Powell's journal are reduced and analysed.

中文翻译：

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1869 年鲍威尔探险队穿越大峡谷的天文观测

在 1869 年沿着格林河和大峡谷探险期间，约翰鲍威尔少校使用六分仪和人造地平线进行天文观测，以确定当时鲜为人知的河流沿线关键点的位置。纬度是从北极星的高度或恒星或土星的子午凌日获得的。当地平均时间是根据对太阳的等高度观测确定的。探险队的一艘小船被淹没毁坏了天文钟，这意味着它们不能用来保持格林威治标准时间并因此找到经度。作为替代，进行了一系列月球距离观测。本文对鲍威尔日记中记录的观察结果进行了简化和分析。