The Art Scroll & Birnbaum siddurim Nusach Ashkenaz for both Rosh Hashannah & Yom Kippur state this ark / opening procedure during the cantor's recital of the Aleinu prayer during Musaph on these 2 holidays:
- Ark is opened at start of the prayer
- Ark is closed during recital of the phrase שלא שם חלקינו כהם - That he did not place our portion among theirs... (and for those that say it, שהם משתחוים *That they bow down...")
- Ark is reopened at ואנחנו כורעים And we bow down
What is the reason for the multiple opening / closing, or why is the ark closed during the 1 or 2 sentences mentioned above?