Passes and Intervals form a fundamental 250-Turn cycle in Pernese history. They are a result of the Red Star's 250-Turn orbit. A Pass is a 50-Turn period during which Thread falls, while the Interval is the period, usually 200 Turns, but in the case of the Long Intervals, 450 Turns, during which Thread does not fall. There have been nine passes and eight intervals so far, and, thanks to the AIVAS' Red Star Diversion Project, the present Pass will be the last one.

This alternation provides a key pattern in Pernese cultural development. At the start of a Pass, the Weyrs grow drastically in prestige and power, due to their sudden renewed importance. Tithes from the Holds and Crafts are increased, and the dragonriders become the most important people on Pern. Some dragonriders do abuse their newfound positions of power, and the early Pass generally is a time of adjustment. During the mid and late Pass, the three fundamental elements of Pernese culture are generally in a balance, in mutual dependence. Once the Pass ends, and the Interval begins, the dragonriders are no longer needed. They continue to receive tithes, out of custom and gratitude, but they are often lower quality, and more grudging. As the Pass fades from living memory into history, the dragonriders' position declines, and they may have difficulty obtaining tithes. Once the Interval ends, the cycle repeats itself.

During the Second Long Interval, the dragonriders' position reached a low point, and, as a result, the Holds and Crafts retained greater rights during the Ninth Pass than during other Passes.

Pass/Interval Equivalent Turns AL
First Pass 8-58
First Interval 58-258
Second Pass 258-308
Second Interval 308-508
Third Pass 508-558
Third Interval 558-758
Fourth Pass 758-808
Fourth Interval
(First Long Interval)
Fifth Pass 1258-1308
Fifth Interval 1308-1508
Sixth Pass 1508-1558
Sixth Interval 1558-1758
Seventh Pass 1758-1808
Seventh Interval 1808-2008
Eighth Pass 2008-2058
Eighth Interval
(Second Long Interval)
Ninth Pass 2508-