Assertion: mercury's sky | /r/HasProperty | dark
Facets:
value: for viewing through telescopes
type: PURPOSE
value: fully
type: DEGREE
Source sentences:
text: Because its rising or setting is always within about two hours of the Sun’s, it is never observable when the sky is fully dark.
text: Whenever the sky is dark enough for viewing through telescopes, Mercury is always already near the horizon, where viewing conditions are poor anyway due to atmospheric factors.