Translation:The sky is clear.
2018-02-09: Perhaps I'm naive, but this seems grammatically correct.
そらがはれています implies a present-continuous tense. "The sky is clearing up."
そらがはれります implies a present tense. "The sky is [being] clear."
Perhaps a question I could ask is, if indeed this sentence is not present-continuous ("clearing"), what indeed is the Japanese sentence for "The sky is clearing up."?
Perhaps something like そらがはれていきます would be "the sky is clearing up." With this case（それがはれています）the います form is signifying the present state of the sky being clear - so it shouldn't be translated as "the sky is clearing" but instead "the sky is clear." Another example, if you say: かれはもう行っています, it means "He is already there" or another way of saying it is "He already went and is there." It's confusing sometimes to know when its progressive usage or to just signify present tense.
～ています can also mean that the verb has changed to and is now in that state.
He has gone to Japan (and is there now).
I (came to) understand it (and am in the state of understanding it).
It took me a while to grasp this.. especially since the form is the same for both action and state verbs in Japanese but different in English. I needed to rework my thinking a bit to try to make things consistent, and the solution I came up with is to treat all usages of the 〜ています form as stative. I.e.
空を晴れています。 The sky is in the state of [being] clear.
私は走っています。 I am in the state of run[ing].
Obviously, I try not to translate it so strangely but understand it intuitively as such.
As far as I know, the plural of sky is used when talking about the sky above different areas, for example countries. I can't say if it is wrong, but it would be unusual to hear in the context of a person perceiving the sky directly above him to be clear. On the other hand when used during a weather report, you could use "The skies are clear" to express, that the skies over several "cities/countries/other area divisions" are clear.
Didn't someone say on another comment (about a plane flying) that ~tearu would be finished but ~teiru would be ongoing. I personally have no clue about this but i would have assumed from that comment that "sora ga hareteimasu" would be something like "the sky is clearing" whereas "sora ga haretearimasu" would be "the sky is being clear" (the action of clearing is over and now it's clear...). But i really don't know...
The issue with removing it "on this lesson" is that the definition probably comes from a general database so they don't have to set up each lesson's definition individually. Depending on the context, each definition is correct. In context of discussing the weather, はれ means sunny. In context of this lesson, clear is more proper.