IC 1805 (also known as the Heart Nebula or by its acronym W4) is a diffuse nebula associated with an open cluster, visible in the constellation Cassiopeia, near the edge of Camelopardalis. Its estimated distance from Earth is about 7500 lightyears; its main characteristic is the presence of two large, apparently empty areas of different sizes, giving the nebula a heart shape. Within it lies a system of small, loosely concentrated open clusters, responsible for the nebula's ionization. The most notable of these is Melotte 15, which contains stars about 50 times more massive than the Sun.

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