When is the best time to observe 100 Herculis?

100 Herculis is best observed from May through July, with peak visibility during June when it transits around midnight in the Northern Hemisphere.

Where is 100 Herculis located in the sky?

100 Herculis lies in the constellation Hercules at right ascension 18h 08m and declination +26° 06′.

What telescope do I need to split 100 Herculis?

Splitting 100 Herculis requires an aperture of roughly 60 mm or larger — the components are separated by about 14.4″ at magnitudes near 5.9. Larger apertures and steady seeing help resolve the pair cleanly.

100 Herculis — Double Star in Hercules

Observable Double Star Excellent (72/100)

Sep: 14.4", Companion: mag 5.8

Magnitude 2.0–6781.0^m DoubleStar Hercules (Her) Visible

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Observe

1Physical Properties

Magnitude 5.86

Spectral Type A3V

Star Color White (B-V 0.12)

Distance 272 ly

2Position & Identifiers

RA 18h 07m 49.5s

Dec +26° 06' 05.0"

Constellation Hercules (Her)

HR 6781

HIP 88818

HD 166045

SAO 85753

Flamsteed 100 Her

Double Cat 11089

SIMBAD

3How easy to split?

Primary 5.9 mag Companion 5.8 mag Separation 14.4″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
150 mm Newton 150mm Newt.	Easy	Easy	Easy
Celestron C8 (203 mm SCT) 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 May – Jul (peak: Jun)

5Multiple Star System Quadruple B: optical

Components 4 (quadruple)

Component IDs AB

Separation 14.4″

Companion Mag 5.8

Position Angle 185°

Star Colors A: White B: White

Discoverer STF2280

Notes

Binary with HR 6782. Primary is speckle binary, sep. 0.106". Component C, 11v at 76". A companion to A at 0.106" | discovered by speckle interferometry.

Separation over time

Measured 1777 → 2023 (246 y)

Separation drift 17.0" → 14.4" (-2.60")

Rate -0.0106" / y

PA drift 180° → 185° (+5°, +0.020°/y)

Slow change over generations — observable in lifetime comparisons.

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.