The very heavens echoed the druid's rage and opened up at his command.[1]
[Starfire] is a direct damage offensive spell that deals a large amount of arcane damage. It is a major part of a BalanceDruid's DPS rotation and accounts for a large amount of overall damage if used properly. It is one of the three abilities ([Starfire], [Starsurge], and [Wrath]) that affect the [Eclipse] mechanic that Balance druids rely on as of patch 4.0.1.
[Glyph of Starfire] causes your Starfire ability to increase the duration of your Moonfire effect on the target by 3 seconds, up to a maximum of 9 additional seconds.
Since [Starfire] is affected by Lunar Eclipse, which in turn is affected by Mastery; Stacking mastery rating will increase the damage of [Starfire] while lunar eclipse is active.
It has the third highest damage per mana of a druid's damage spells, after [Moonfire] (DOT included) and [Insect Swarm]. Thus it is an optimal offensive ability to use when running low on mana.
Past changes
Patch 4.0.1 (2010-10-12): Starfire is available at level 8 for 3 70.