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Xi Tauri — Double Star in Taurus

Magnitude 3.7m DoubleStar Taurus (Tau) Visible
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1Physical Properties

Magnitude 3.74
Spectral Type B7.5V
Star Color Blue-white (B-V -0.09)
Distance 221 ly

2Position & Identifiers

RA 03h 27m 10.2s
Dec +09° 43' 58.0"
Constellation Taurus (Tau)
HR 1038
HIP 16083
HD 21364
SAO 111195
Bayer Xi
Flamsteed 2 Tau
SIMBAD

3How easy to split?

Primary 3.7 mag Companion 7.6 mag Separation 0.6″
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Telescope Bortle 3 Bortle 4 Bortle 5
80mm refr. V. hard V. hard V. hard
150mm Newt. V. hard V. hard V. hard
C8 203mm V. hard V. hard V. hard
Easy Medium Hard Very hard Impossible

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

To reach "Medium" at Bortle 3, you'd need at least a 720 mm reflector.

4Visibility

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Best season Oct – Dec (peak: Nov)

5Multiple Star System

Separation 0.6″
Companion Mag 7.5
Position Angle 273°
Star Colors A: Blue-white B: Blue-white
Discoverer HDS 433

Separation over time

Period: 50.8 y Eccentricity: 0.571 Now: 0.64", PA 280° + 0.04" in 5 years
0.00" 0.20" 0.40" 0.59" 0.79" 2025 2030 2035 2040 2045 0.64"

Apparent separation over time, computed from ORB6 orbital elements. Steep curves indicate fast-changing pairs — catch them while they're splittable.

Eyepiece View

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80x Dawes: 1.9″ TFOV: 0.6°
Realistic = true angular size
N E 273°

A: 3.7 · B: 7.5 · Sep: 0.6″ · PA: 273° · N up, E right

Unresolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″

Explore

7

Size Comparison

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8

Compare Stars

9

Spectral Classification

10

Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map
11

Stellar Lifecycle

12

Blackbody Spectrum

13

Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

14

Stellar Fusion

Discover

15Stellar Notes

Triple Sp. system of 2 sharp-line stars revolving in 7.1466d; this pair revolves in 145.10d around broad-line B7 star.
B8Vn+B8Vn+B7Vn.
16

Light Travel Time Machine

17

Relativistic Travel

Nearby in the Sky

Other targets within a few degrees — pan your scope a little and keep exploring.

Visibility scores assume a 150 mm Newton at Bortle 4.

NGC 1218
Hard+
Bright spiral galaxy
Galaxy mag 12.8 7.3° Cetus
Lambda Tau
Medium
Eclipsing binary, period 4.0d
Variable Star mag 3.47 8.7° Taurus
V711 Tau
Easy
Easy double, sep 6.7″
Double Star mag 5.71 9.5° Taurus
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