When is the best time to observe Alcyone?

Alcyone is best observed from October through December, with peak visibility during November when it transits around midnight in the Northern Hemisphere.

Where is Alcyone located in the sky?

Alcyone lies in the constellation Taurus at right ascension 03h 47m and declination +24° 06′.

What telescope do I need to split Alcyone?

Splitting Alcyone requires an aperture of roughly 60 mm or larger — the components are separated by about 117.6″ at magnitudes near 2.9. The companion is about 3.4 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Alcyone — Double Star in Taurus

HIP 17702; Eta Tauri; 25 Tauri

Observable Double Star Good (52/100)

Sep: 117.6", Companion: mag 6.3

Magnitude 2.9^m DoubleStar Taurus (Tau) Visible

Star Map + List + Plan

About Alcyone

Description

Alcyone is a blue-white giant of spectral type B7IIIe at magnitude 2.87, the brightest star in the Pleiades star cluster (M45) in Taurus. Located about 440 light-years from Earth, it has a luminosity of roughly 2,400 times solar. Alcyone is a Be star, surrounded by a gaseous disk from rapid rotation.

Observing Tips

Alcyone is the most prominent member of the Pleiades, the bright star at the center of the cluster's distinctive pattern. In binoculars, the Pleiades cluster is a stunning sight with Alcyone as its jewel. Best observed October through March.

History

Named after one of the seven daughters of Atlas and Pleione in Greek mythology. The Pleiades cluster and Alcyone in particular have been culturally significant worldwide — referenced in the Bible, Homer, and the astronomical traditions of dozens of cultures. The Japanese name 'Subaru' for the cluster is used by the car manufacturer.

Fun Facts

Alcyone is surrounded by a gas disk and a reflection nebula — the blue haze visible in long-exposure photographs of the Pleiades is starlight scattered by interstellar dust that the cluster happens to be moving through.

Observe

1Physical Properties

Magnitude 2.87

Spectral Type B7III giant

Star Color Blue-white (B-V -0.09)

Distance 408 ly

2Position & Identifiers

RA 03h 47m 29.1s

Dec +24° 06' 18.0"

Constellation Taurus (Tau)

HR 1165

HIP 17702

HD 23630

SAO 76199

Bayer Eta

Flamsteed 25 Tau

SIMBAD Wikipedia

3How easy to split?

Primary 2.9 mag Companion 6.3 mag Separation 117.6″

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
150 mm Newton 150mm Newt.	Easy	Easy	Easy
Celestron C8 (203 mm SCT) C8 203mm	Easy	Easy	Easy

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

Set a location in User Settings to see visibility data.

Best season Oct – Dec (peak: Nov)

5Multiple Star System Quintuple D,E,F,G,H: optical

Components 5 (quintuple)

Component IDs O

Separation 117.6″

Companion Mag 6.3

Companion Sp A4V

Position Angle 291°

Star Colors A: Blue-white B: White

Discoverer STFA 8

Notes

Component A is occultation double, sep. 0.031". B, C, D, 8.1 A0V, 8.1 Am(A5/F0/F2) and 8.7v F2V at 117" to 190". | Possibly second occultation companion at 0.001", unresolved by speckle interferometry. vsini of B 155k/s. Numerous | photometric determinations yield 6.3 for B component. The HD gives 8.1 for 23629 and the IDS indicates 8.1. Burnham, | Double Stars, gave 7.0 vis.

Separation over time

Measured 1836 → 2016 (180 y)

Separation drift 117.1" → 117.6" (+0.50")

Rate +0.0028" / y

PA drift 289° → 291° (+2°, +0.011°/y)

Essentially fixed on human timescales — the same view your grandchildren will see.

Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.