Complete the given passage.

The principle ……………………. (behind / over / for) an astronomical calendar is simple. The apparent rising and setting horizon point of the sun …………………….. (changes / is changing / has changed) with each passing day. The different points …………………….. (correspond / corresponds / are corresponding) to different days of the year.

 At minimum, an astronomical calendar only ……………………. (is requiring / requires / has required) a fixed reference point for viewing and another fixed reference point for marking the position of the rising and/or setting sun …………………… (on / in / at) the horizon.

 In the Northern Hemisphere, the winter solstice …………………….. (marks / is marking / mark) the southern limit of the sun’s journey and the summer solstice is the northern boundary.

Solution

The principle behind an astronomical calendar is simple. The apparent rising and setting horizon point of the sun changes with each passing day. The different points correspond to different days of the year.

 At minimum, an astronomical calendar only requires a fixed reference point for viewing and another fixed reference point marking the position of the rising and/or setting sun on the horizon.

In the Northern Hemisphere, the winter solstice marks the southern limit of the sun’s journey and the summer solstice is the northern boundary.