FWP:
SETS == MUSHAIRAH;
WORDPLAY
CLOTHING/NAKEDNESS: {3,5}
SKY {15,7}
VEIL: {6,1}
As Bekhud Mohani observes, this is a verse built almost entirely on wordplay. It's also what I would call a classic 'mushairah verse'. From the first line, the listener can't tell what's coming next, and must wait during the mushairah's suitably suspenseful oral-performance interval between lines. Even when the second line is vouchsafed, the punch-word doesn't appear until the last possible moment.
In the first line, we hear of the 'Daughters of the Bier', who all day remain, with apparent chastity and rectitude, in the seclusion of pardah. Thinking of them as 'daughters' makes us feel that they're living discreetly and quietly in their father's house. But of course, the 'Daughters of the Bier' is the Arabic name for the constellation Ursa Major, the 'Great Bear'.
Even in the second line, we're starved of information until the last possible moment: 'at night, what came into their heads, that they --became NAKED?! (For a discussion of Ghalib's uses-- and positioning-- of the word 'naked' [((uryaa;N], see {6,1}.) And then, when you suddenly 'get' it, you've got it entirely, and surely with a laugh. A real 'mushairah' verse neither demands nor rewards much further reflection.
The second line is in Ghalib's favorite interrogative form of his favorite inshaa))iyah mode of speech. We immediately recognize it as a rhetorical question, however. What came into their mind? Well, we all know, don't we! The verse, with a clever show of naive innocence, enlists our own erotic memory and imagination into its service. This is one of Ghalib's elegantly indirect erotic verses; for others, see {99,4}. What other poet could make something so witty and sexy from such seemingly mild material as the idea of the stars coming out?
Compare the mileage that Mir gets from similar innuendo about the 'Daughter of the Vine': M{584,7}.
Note for grammar fans: In the second line, the feminine singular aa))ii is agreeing with a colloquially-omitted baat . For more on this, see {59,4}.
Nazm:
He expresses the mood of the stars' coming out; he has constructed it as 'becoming naked'. The Daughters of the Bier are seven stars visible in the north. Four stars among them are the bier, and three are the bearers of it. (116)
== Nazm page 116; Nazm page 117