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HIP 21756 — Double Star in Dorado

Magnitude 6.5m DoubleStar Dorado (Dor) Visible
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1Physical Properties

Magnitude 6.53
Spectral Type G5V
Star Color Orange (B-V 0.68)
Distance 51 ly

2Position & Identifiers

RA 04h 40m 18.3s
Dec -58° 56' 37.0"
Constellation Dorado (Dor)
HR 1504
HIP 21756
HD 30003
SAO 233622
SIMBAD

3How easy to split?

Primary 6.5 mag Companion 7.5 mag Separation 3.9″
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Telescope Bortle 3 Bortle 4 Bortle 5
80mm refr. Medium+ Medium+ Medium+
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

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Best season Oct – Dec (peak: Nov)

5Multiple Star System

Separation 3.9″
Companion Mag 7.5
Position Angle 90°
Star Colors A: Orange B: Orange
Discoverer HJ 3683
7.2 G5V, 7.3 G6V, 552.30y, a = 3.164". Combined mag., colors. Both components also classified G3V.

Separation over time

Period: 326.2 y Eccentricity: 0.950 Now: 3.9", PA 89° + 0.07" in 5 years
0.00" 1.2" 2.4" 3.6" 4.8" 2025 2030 2035 2040 2045 3.9"

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 90°

A: 6.5 · B: 7.5 · Sep: 3.9″ · PA: 90° · N up, E right

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

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6

Size Comparison

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8

Spectral Classification

9

Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map
10

Stellar Lifecycle

11

Blackbody Spectrum

12

Stellar Absorption Spectrum

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

13

Stellar Fusion

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14Stellar Notes

0.038".
15

Light Travel Time Machine

16

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 1574
Easy
Elliptical galaxy
Galaxy mag 10.5 3.1° Reticulum
R Dor
Easy
Semi-regular variable, range 4.8–6.6
Variable Star mag 5.40 3.2° Dorado
Theta Ret
Easy
Easy double, sep 4.1″
Double Star mag 5.87 5.1° Reticulum
NGC 1868
Medium
Compact globular cluster
Globular Cluster mag 11.57 6.5° Dorado
Show on Map

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