The amount of sky that you can view through a telescope is called the real (true) field of view and is measured in degrees of arc (angular field).
通过望远镜你所能看到的天空的范围称作真实视场,以弧度值(角视场)来度量。
Yellowstone is at the northeastern end of the Snake River Plain, a great U-shaped arc through the mountains that extends from Boise, Idaho some 400 miles (640 km) to the west.
黄石公园是在蛇河平原的东北端。蛇河平原是一个巨大的U弧形,由爱达荷州的博伊西山脉向外延伸出来的群山向西大约400英里(640公里)。
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