When is the best time to observe 102 Herculis?

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

Where is 102 Herculis located in the sky?

102 Herculis lies in the constellation Hercules at right ascension 18h 09m and declination +20° 49′.

What telescope do I need to split 102 Herculis?

Splitting 102 Herculis requires an aperture of roughly 60 mm or larger — the components are separated by about 23.1″ at magnitudes near 4.4. The companion is about 7.4 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

102 Herculis — Double Star in Hercules

Magnitude 4.4^m DoubleStar Hercules (Her) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.36

Spectral Type B2IV subgiant

Star Color Blue (B-V -0.16)

2Position & Identifiers

RA 18h 08m 45.5s

Dec +20° 48' 52.0"

Constellation Hercules (Her)

HR 6787

HIP 88886

HD 166182

SAO 85769

Flamsteed 102 Her

Double Cat 11102

SIMBAD

3How easy to split?

Primary 4.4 mag Companion 11.8 mag Separation 23.1″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Hard	V. hard+	V. hard
150 mm Newton 150mm Newt.	Medium	Hard+	Hard
Celestron C8 (203 mm SCT) C8 203mm	Medium+	Medium	Hard+

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

Separation 23.1″

Companion Mag 11.8

Position Angle 137°

Star Colors A: Blue

Discoverer AGC 8

Notes

Companion A6V, optical.

Separation over time

Measured 1878 → 2023 (145 y)

Separation drift 23.4" → 23.1" (-0.30")

Rate -0.0021" / y

PA drift 137° → 137° (+0°, +0.000°/y)

Essentially fixed on human timescales — the same view your grandchildren will see.

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.