Crux

Crux
Abbreviation	Cru
Genitive	Crucis
Meaning in English	Southern cross
Right ascension	12 h
Declination	-60°
Visible to latitude	Between 20° and -90°
Evening visibility	May
Area  - Total	Ranked 88th 68 sq. deg.
Number of stars with apparent magnitude < 3	4
Brightest star  - Apparent magnitude	Mimosa (β Cru) 1.23
Meteor showers	Crucids
Bordering constellations	Centaurus Musca

Crux, the cross, commonly known as the Southern Cross (in contrast to the Northern Cross), is the smallest of the 88 modern constellations, but also one of the most famous.

Table of contents

1 Notable features 2 Notable deep sky objects 3 History

Notable features

Its five brightest stars (α, β, γ, δ and ε Crucis) appear on the flags of Australia, Brazil, New Zealand, Papua New Guinea and Samoa, except that the New Zealand flag omits Epsilon.

With the the lack of a significant pole star in the southern sky (σ Octantis is closest to the pole, but is so faint as to be useless for the purpose), two of the stars of Crux (Alpha and Gamma, Acrux and Gacrux respectively) are commonly used to mark south. Following the line defined by the two stars for approximately four times the distance between them leads to a point close to the Southern Celestial Pole.

Alternatively, if a line is constructed perpendicularly between α Centauri (Toliman) and β Centauri, where the above line and this line intersect marks the Southern Celestial Pole.

Notable deep sky objects

The Coalsack Nebula is the most prominent dark nebula in the skies, well visible to the naked eye as big dark patch in the southern Milky Way.

Another deep sky object within Crux is the open cluster NGC 4755. This Jewel Box was discovered by Nicolas Louis de Lacaille in 1751-1752.

History

Crux was formerly part of Centaurus, and was first introduced as a separate constellation by A. Royer in 1679. Due to precession of the equinox, Crux and Centaurus were visible from the Mediterranean area in antiquity, so their stars had to be known by Greek astronomers.