When is the best time to observe Tau Eridani?

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

Where is Tau Eridani located in the sky?

Tau Eridani lies in the constellation エリダヌス at right ascension 03h 20m and declination -21° 45′.

What telescope do I need to split Tau Eridani?

Splitting Tau Eridani requires an aperture of roughly 80 mm or larger — the components are separated by about 5.8″ at magnitudes near 3.7. The companion is about 5.8 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Tau Eridani — エリダヌスの二重星

HIP 15474; Tau4 Eridani; 16 Eridani

等級 3.6–3.7^m DoubleStar エリダヌス (Eri) 可視

星図 + リスト + 計画

Tau Eriについて

説明

Tau Eridani is a red giant of spectral class M3 III-IIIa Ca-1 about 304 light-years away. It shines at magnitude 3.69 and is a semiregular variable, with brightness variations of about 0.1 magnitudes on a 30-day period. Tau Eri is a mature asymptotic-giant-branch star approaching the end of its life.

観測のコツ

Tau Eri sits in the northern part of Eridanus. Its deep orange-red color is striking in binoculars. Long-term amateur monitoring can track the variability, though the amplitude is modest. Best observed October through February.

歴史

Tau Eri retains its Bayer designation in current IAU catalogs.

豆知識

Tau Eri's M3 spectrum shows strong molecular absorption bands from titanium oxide, calcium hydride, and other molecules — signatures of the cool outer envelope of a red giant. Its mass-loss rate is high enough that the star is shedding material into a growing circumstellar shell.

観測

1物理的性質

等級 3.69

範囲 3.57 - 3.78

周期 23.8 日

変光星タイプ Semi-Regular Variable (Short Period)

スペクトル型 M3III-IIIa Ca-1 巨星

星の色赤 (B-V 1.62)

距離 304 ly

2位置と識別子

RA 03h 19m 31.0s

Dec -21° 45' 28.0"

星座エリダヌス (Eri)

HR 1003

HIP 15474

HD 20720

SAO 168460

Bayer Tau4

Flamsteed 16 Eri

Variable ID Tau4 Eri

Double Cat 2472

SIMBAD Wikipedia

3分離しやすさ

主星 3.7 mag 伴星 9.5 mag 離角 5.8″

サインインし、機材と既定の場所を設定するとパーソナライズ行が表示されます。

望遠鏡	ボートル3	ボートル4	ボートル5
80 mm 屈折 80mm 屈折	極難+	極難+	極難+
150 mm ニュートン 150mm ニュートン	困難+	困難+	困難+
Celestron C8 (203 mm SCT) C8 203mm	普通	普通	普通