An Equinox Power Blade was one of a set of twin Power Swords used by the Space Marines of the Great Crusade and Horus Heresy eras. The set was divided into a "Sunrise Blade" and a "Sunset Blade", each of which had slightly different combat characteristics.
The pair were wielded together by a single Astartes in melee combat. The Sunrise Blade was effective at shredding flesh, while the Sunset Blade was capable of sundering even the hardest of substances.
- The Horus Heresy - Book Eight: Malevolence (Forge World Series) by Neil Wylie and Anuj Malhotra, pg. 206