Menu

Theta Eridani — Double Star in Eridanus

HIP 13847; Theta2 Eridani

Observable Double Star Excellent (71/100)

Sep: 8.3", Companion: mag 4.1

Magnitude 4.3m DoubleStar Eridanus (Eri) Visible
Star Map
+ List + Plan

Observe

1Physical Properties

Magnitude 4.35
Spectral Type A5 III giant
Star Color Yellow-white (B-V 0.08)
Distance 161 ly

2Position & Identifiers

RA 02h 58m 16.3s
Dec -40° 18' 16.0"
Constellation Eridanus (Eri)
HR 898
HIP 13847
HD 18623
SAO 216114
Bayer Theta2
SIMBAD Wikipedia

3How easy to split?

Primary 4.4 mag Companion 4.1 mag Separation 8.3″
Sign in and configure your equipment and default location to see a personalized row.
Telescope Bortle 3 Bortle 4 Bortle 5
80mm refr. Easy Easy Easy
150mm Newt. Easy Easy Easy
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 Sep – Nov (peak: Oct)

5Multiple Star System

Separation 8.3″
Companion Mag 4.1
Star Colors A: Yellow-white B: White
Binary with HR 897.

Eyepiece View

Log in to set your own equipment
80x Dawes: 1.9″ TFOV: 0.6°
Realistic = true angular size
N E

A: 4.3 · B: 4.1 · Sep: 8.3″ · PA: ? · N up, E right

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

Explore

7

Size Comparison

Querying VizieR for stellar data…
8

Compare Stars

9

Spectral Classification

10

Hertzsprung-Russell Diagram

Loading HR diagram…
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

0.016".
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.

Acamar
HIP 13847; Theta1 Eridani
Easy
Easy double, sep 8.2″
Double Star mag 3.24 0.0° Eridanus
IC 1875
Hard+
Elliptical galaxy
Galaxy mag 12.55 1.4° Fornax
Show on Map

Explore Nightbase

Related knowledge, tools, and stories — no observation planning required.

Eridanus
Mythology, bright stars, and deep-sky highlights.
Constellation
Double Stars — A Guide for Observers
Two suns where one appeared — how to find, split, and appreciate the night sky's finest pairs. From Albireo's gold-and-blue to the Sirius B challenge.
Article
Venus
Phases, transits, and the brightest planet in the sky.
Deep dive
}