When is the best time to observe 42 Herculis?

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

Where is 42 Herculis located in the sky?

42 Herculis lies in the constellation Hercules at right ascension 16h 39m and declination +48° 56′.

What telescope do I need to split 42 Herculis?

Splitting 42 Herculis requires an aperture of roughly 60 mm or larger — the components are separated by about 28.1″ at magnitudes near 4.9. The companion is about 6.9 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

42 Herculis — Double Star in Hercules

Magnitude 4.9^m DoubleStar Hercules (Her) Visible

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1Physical Properties

Magnitude 4.90

Spectral Type M2.5IIIab bright giant

Star Color Red (B-V 1.55)

Distance 192 ly

2Position & Identifiers

RA 16h 38m 44.9s

Dec +48° 55' 42.0"

Constellation Hercules (Her)

HR 6200

HIP 81497

HD 150450

SAO 46210

Flamsteed 42 Her

Double Cat 10144

SIMBAD

3How easy to split?

Primary 4.9 mag Companion 11.8 mag Separation 28.1″

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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 Apr – Jun (peak: May)

5Multiple Star System

Separation 28.1″

Companion Mag 11.8

Position Angle 92°

Star Colors A: Red

Discoverer STF2082

Notes

Optical.

Separation over time

Measured 1782 → 2020 (238 y)

Separation drift 21.5" → 28.1" (+6.60")

Rate +0.0277" / y

PA drift 94° → 92° (-2°, -0.008°/y)

Apparent motion is significant on a human timescale — worth revisiting in a decade.

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.