Albireo is a showpiece double star and one of the great small telescope objects. To the naked eye, it's the fifth brightest star in Cygnus (combined mag. +2.9) and the lone star that marks the head of "the Swan" constellation. When viewed through small scopes - or even good 10x50 binoculars - it splits into two components. The primary shines at mag. +3.1 (Albireo A) and the secondary at mag. +5.1 (Albireo B). The stars are separated by a generous 34.3 arc seconds, but what makes this special is the vivid colour contrast between the two components. A brilliant yellow primary, accompanied by a soft blue secondary.

Albireo is a striking double star through amateur telescopes (credit:- freestarcharts)

Cygnus represents a Swan flying down the plane of the Milky Way. It contains many bright stars. Positioned at its heart is a prominent asterism in the shape of a large cross, hence the name "Northern Cross". Located at the northern end of the cross is the constellation's brightest star, blue-white supergiant Deneb (α Cyg - mag. +1.3). At the opposite end lies Albireo.

Finder Chart for Albireo (credit:- freestarcharts)

Finder Chart for Albireo - pdf format (credit:- freestarcharts)

Albireo is easily split with small telescopes at low powers. The surrounding field of view also contains numerous fainter stars, adding to the splendour. At high magnifications, the separation of the two stars is plentiful. Larger scopes improve the colour contrast with many more fainter background stars also visible.

Albireo is located about 430 light-years from the Earth. It's unclear if Albireo A and B are actually a physical binary system. If so, the orbital period would be at least 100,000 years. In 1976, using speckle interferometry it was discovered that Albireo A is a binary star itself. In the Washington Double Star Catalogue, this pair is designated as Aa and Ac with a separation of 0.4 arc seconds. The resolution capability of the average size amateur scope won't split them, but those with extremely large reflectors of the order of 500mm (20-inch) aperture or more may be able to do so under exceptional seeing conditions.

Albireo is a must see object and one of the finest double stars in the night sky. Its beauty comes from the striking colour contrast of the component stars, a brilliant yellow primary and a soft blue secondary. With a wide separation, the double is easily split with small telescopes and even good binoculars. As a result, it's a favourite target for amateur astronomers.

Albireo Data Table

NameAlbireo
Apparent Magnitude2.90
ComponentsA (Aa and Ac) and B
Angular separation (arc secs)35.3 (AB), 0.4 (AaAc)
Position angle (degrees)54 (AB)
Other DesignationsBeta Cygni, β Cyg

Albireo A Components Data Table

NameAlbireo AaAlbireo Ac
Washington Double Star Catalogue (WDS)19307+2758Aa19307+2758Ac
HD183912183913
HIP9594795947
SAO8730187301
Flamsteed6 Cygni A6 Cygni A
ConstellationCygnusCygnus
RA (J2000)19h 30m 43.286s19h 30m 43.295s
DEC (J2000)+27d 57m 34.84s+27d 57m 34.62s
Apparent Magnitude+3.18+5.82
Apparent Magnitude Aa and Ac Combined+3.08+3.08
Absolute Mag.-2.45-0.25
Distance (light-years)430430
Mass (Solar)5.03.2
Radius (Solar)703.5
Luminosity (Solar)1,200230
Temperature (K)4,08012,000
Spectral typeK2IIB8:p
Other DesignationsBeta Cygni A, β Cyg ABeta Cygni A, β Cyg A

Albireo B Component Data Table

NameAlbireo B
Washington Double Star Catalogue (WDS) 19307+2758B
HD183914
HIP95951
SAO87302
Flamsteed6 Cygni B
ConstellationCygnus
RA (J2000)19h 30m 45.395s
DEC (J2000)+27d 57m 55.00s
Apparent Magnitude+5.09
Absolute Mag.-0.35
Distance (light-years)400
Mass (Solar)3.7
Radius (Solar)2.7
Luminosity (Solar)230
Temperature (K)13,200
Spectral TypeB8Ve
Other DesignationsBeta Cygni B, β Cyg B

Sky Highlights - September 2017

Opposition
Neptune reaches opposition on September 5th

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for September

Northern Hemisphere
Evening
West:- Jupiter (mag. -1.7)
Southwest:- Saturn (mag. +0.5)
East:- Neptune (mag. +7.8)
Midnight
South:- Neptune
East:- Uranus (mag. +5.7)
Morning
West:- Neptune
South:- Uranus
East:- Venus (mag. -3.9), Mars (mag. +1.8) (from second week), Mercury (mag. +0.5 to -1.3) (from second week)

Southern Hemisphere
Evening
West:- Jupiter
Northwest:- Saturn
East:- Neptune
Midnight
West:- Saturn
North:- Neptune
Northeast:- Uranus
Morning
West:- Neptune
Northwest:- Uranus
Northeast:- Venus
East:- Mars (end of month)

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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