Assertion: reflecting telescope's mirror | /r/HasProperty | cleaned
Facets:
value: occasionally
type: DEGREE
value: periodically
type: TEMPORAL
value: because of their size
type: CAUSE
value: always
type: DEGREE
Source sentences:
text: Because they are normally open, the mirrors have to be cleaned.
text: Each working day, two segments will be re-coated and replaced to ensure the mirror is always clean and highly reflective.
text: Because of their size and the design of an open tube assembly, the mirror must be cleaned periodically.
text: Easy and economical to build Can be made larger Disadvantages Not enclosed, so mirrors need to be cleaned occasionally
text: Not enclosed, so mirrors need to be cleaned occasionally