When is the best time to observe Ain?

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

Where is Ain located in the sky?

Ain lies in the constellation Taurus at right ascension 04h 29m and declination +19° 11′.

What telescope do I need to split Ain?

Splitting Ain requires an aperture of roughly 60 mm or larger — the components are separated by about 190.4″ at magnitudes near 3.5. The companion is about 7.1 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Ain — Double Star in Taurus

HIP 20889; Epsilon Tauri; 74 Tauri

Magnitude 3.5^m DoubleStar Taurus (Tau) Visible 1 Exoplanet

Star Map + List + Plan

About Ain

Description

Ain, Epsilon Tauri, is a K-giant of spectral class G9.5 III about 147 light-years away. It is a member of the Hyades open cluster and became famous in 2007 as the first Hyades star confirmed to host an exoplanet — Ain b, a super-Jupiter of at least 7.6 Jupiter masses in a 1.6-year orbit. Ain's magnitude is 3.53 and its color is a warm pale orange.

Observing Tips

Ain marks the northern eye of the Taurus bull, above the V of the Hyades. In any small binoculars it appears as a warm yellow-orange point surrounded by dozens of fainter Hyades members. Ain is one of the "bull's eyes," with Aldebaran marking the southern eye. Best observed November through March.

History

The name Ain is Arabic for "eye," specifically designating the bull's northern eye. The pairing of Aldebaran ("the follower") and Ain ("the eye") in Taurus dates to pre-Islamic Arabic astronomy. The IAU adopted both names in 2016.

Fun Facts

Ain's planet was the first exoplanet discovered around a Hyades member — a milestone because the Hyades is the closest well-studied open cluster, allowing direct comparison of planetary-system outcomes in a co-evolving population of stars. The 625-million-year-old age of the Hyades means Ain b is a "young Jupiter," useful for studying how giant planets evolve over cosmic time.

Observe

1Physical Properties

Magnitude 3.53

Spectral Type G9.5III CN0.5 giant

Star Color Orange (B-V 1.01)

Distance 147 ly

2Position & Identifiers

RA 04h 28m 37.0s

Dec +19° 10' 49.0"

Constellation Taurus (Tau)

HR 1409

HIP 20889

HD 28305

SAO 93954

Bayer Epsilon

Flamsteed 74 Tau

SIMBAD Wikipedia

3How easy to split?

Primary 3.5 mag Companion 10.6 mag Separation 190.4″

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

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

Separation 190.4″

Companion Mag 10.6

Position Angle 269°

Star Colors A: Orange

Discoverer BUP 61

Separation over time

Measured 1894 → 2015 (121 y)

Separation drift 179.9" → 190.4" (+10.50")

Rate +0.0868" / y

PA drift 268° → 269° (+1°, +0.008°/y)

Apparent motion is significant on a human timescale — worth revisiting in a decade.

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.