The optimum single target DPS rotation is as follows, Starsurge on cooldown.
Start fight one cast pre-Lunar.
Nature's Vigil (if you have it)
Starfall (when first Starfall duration ends)
Starfire until 0 energy
Starfall (when second Starfall duration ends)
Moonfire (Sunfire will automatically be applied)
Starfire (utilize shooting stars procs)
Refresh Moonfire immediately before Celestial Alignment expires
Starfire to Solar Eclipse
Wrath until Lunar Eclipse.
Rinse and repeat (from the 'Starfall' below Celestial Alignment)