Crux

Crux is a compact constellation in the southern sky whose four brightest stars form the Southern Cross, a prominent pattern used for celestial navigation.

Acrux: Acrux is the brightest star in Crux, a blue multiple-star system about 320 light-years from Earth. It marks the foot of the Southern Cross and gives Crux its brightest point.
Southern Cross: The Southern Cross is the cross-shaped asterism formed mainly by Crux's four brightest stars. It is the recognizable pattern at the heart of the constellation.
Ptolemy: Ptolemy was a second-century Greek astronomer whose star catalogue recorded 48 constellations. Crux's stars appeared in his catalogue as part of the larger Centaurus.
Coalsack Nebula: The Coalsack Nebula is a dark cloud of interstellar dust visible against the Milky Way near Crux. It lies beside the Southern Cross and appears as a conspicuous dark patch.
Mimosa: Mimosa is a blue giant star and the second-brightest star in Crux. It forms the eastern arm of the Southern Cross.
Celestial navigation: Celestial navigation determines position or direction by observing celestial bodies. Crux helps observers estimate the direction of the south celestial pole.
Petrus Plancius: Petrus Plancius was a Dutch cartographer who helped introduce several southern constellations to European star maps. His late-sixteenth-century maps helped establish Crux as a separate constellation.
Jewel Box Cluster: The Jewel Box is an open star cluster in Crux, catalogued as NGC 4755. It is a prominent deep-sky object within the constellation's boundaries.
Gacrux: Gacrux is a red giant star and the northernmost bright star in Crux. Its contrasting color makes the top of the Cross distinctive.
South celestial pole: The south celestial pole is the point in the sky directly above Earth's South Pole. Extending the Cross's long axis points approximately toward this pole.

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