The sky being clear of clouds, the astronomer continued further observation.
Why would JMurray delete a post? I was here while I was writing mine. Now it's gone. It needed a tweak.
Here's a scenario in which the indefinite article is feasible, not highly likely but feasible. The writer is observing a number of people going about their activities in a park. I don't think "further" adds anything so I hope you don't mind if I delete it for my version.
"It had been overcast for several minutes but eventually the wind picked up and the early evening light improved for a few moments. A young boy flew his kite one last time, a tired jogger headed for home and, the sky being clear of clouds, an astronomer continued his observation of the darkening sky".
OR
".. the sky having cleared of clouds, an astronomer continued his observation..".
If you were to choose, would you choose "being......" or "having cleared....."?
To reinforce the point that the astronomer had stopped observing for a while and then started again I might go for "the sky having cleared of clouds" or just "the sky having cleared", it's the flow of events.
not a teacher