Constellations: Apus 'the Bird of Paradise'

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Name:	Apus (Latin: 'bird of paradise')
Genitive:	Apodis
Short form:	Aps
Area:	206 sq deg
Co-ordinates¹:	Right Ascension 16^h, Declination −75°
Origin:	Modern

Apus, the Bird of Paradise, is a southern, circumpolar constellation lying between the southern celestial pole constellation of Octans and the prominent triangle of stars that make up Triangulum Australe, the 'Southern Triangle' constellation. Apus is faint and does not present any readily identifiable shape, although three of its brighter stars can be seen as a small triangle.

History

In the late 16th Century, the Dutch East India Company were exploring the far southern hemisphere latitudes for trading opportunities. During the 1595 expedition, Pieter Dirkszoon Keyser and Friedrich de Houtmann recorded the positions of 196 stars near the south celestial pole that had previously been unseen by northern-based astronomers. These stars were later formed into twelve new constellations and were adopted by astronomer Johann Bayer in his star atlas of 1603, Uranometria, to fill in unnamed areas of the southern sky. Bayer attributed the name Apus Indica - or Bird of India - to tales by early Dutch seafarers, who had recorded that gifts of live birds were made to European travellers.

It is the Bird of Paradise that is depicted in Uranometria, but another interpretation originates from the Greek word 'apous', meaning without feet. This refers to the European Swift, which was reputed not to have any legs as it was always seen to be in flight and never alighting.

Principal Stars

Because of its far south position in the sky, near to the southern celestial pole, the stars of Apus were not seen by the ancient astronomers. Consequently none of its stars were given proper names, and are therefore known only by their attributed Greek letter classification.

None of the stars in Apus are brighter than alpha Aps - an orange giant at +3.81 magnitude. Delta Aps is a widely spaced double star, both components of which are orange giants that can be readily seen with binoculars; the primary of the pair is an irregular variable between +4.7 and +4.9 magnitude² with an orange colour biased towards red, while the secondary is +5.3 magnitude and orange in colour.

Kappa Aps is another double, although slightly fainter with magnitudes of +5.37 and +5.62. Theta Aps is a variable star of +6.4 magnitude, dimming to +8.6 every 119 days.

Star Chart

Star	Name	Magnitude	Distance (light years)	Remarks
α Aps	alpha Aps	+3.81	413	Orange
γ Aps	gamma Aps	+3.84	160	Yellow G-type giant
β Aps	beta Aps	+4.21	159	Double. Orange primary
δ Aps	delta Aps	+4.65 and +5.3	767	Double star. Orange/Red giants
κ Aps	kappa Aps	+5.37 and +5.62	1019 and 741	Double star
θ Aps	theta Aps	+6.4 to +8.6	329	Variable star

Globular Star Cluster

NGC 6101 is a faint globular star cluster of about 9th magnitude that lies north of gamma Aps.

Catalogue	Type	Magnitude	Remarks
NGC 6101	Globular cluster	+9.1	+50,000 stars

Extrasolar Planets

In 2011 an extrasolar planet was discovered in Apus. HD 137388 b orbits its parent star, orange dwarf HD 137388, in 330 days.

Another Bird of Paradise

In addition to the constellation Apus, there is also a remarkable flower that has been named from the avian Bird of Paradise. The Strelitzia shares the name due to its beautiful crimson, orange and yellow flower that resembles the plumage of the bird. It is very difficult to grow the flower outside of South Africa, its home environment.

¹Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.²A measure of the apparent (rather than the actual) brightness of the star. Magnitude 1 is brighter than magnitude 10.

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