When is the best time to observe 39 Leonis?

39 Leonis is best observed from January through March, with peak visibility during February when it transits around midnight in the Northern Hemisphere.

Where is 39 Leonis located in the sky?

39 Leonis lies in the constellation Leo at right ascension 10h 17m and declination +23° 06′.

What telescope do I need to split 39 Leonis?

Splitting 39 Leonis requires an aperture of roughly 80 mm or larger — the components are separated by about 7.8″ at magnitudes near 5.8. The companion is about 5.5 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

39 Leonis — Double Star in Leo

Magnitude 5.8^m DoubleStar Leo Visible

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Observe

1Physical Properties

Magnitude 5.82

Spectral Type F8Vb w

Star Color Yellow (B-V 0.50)

Distance 53 ly

2Position & Identifiers

RA 10h 17m 14.6s

Dec +23° 06' 22.0"

Constellation Leo

HR 4039

HIP 50384

HD 89125

SAO 81270

Flamsteed 39 Leo

Double Cat 7712

SIMBAD

3How easy to split?

Primary 5.8 mag Companion 11.3 mag Separation 7.8″

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

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Jan – Mar (peak: Feb)

5Multiple Star System

Separation 7.8″

Companion Mag 11.3

Companion Sp M1.5

Position Angle 300°

Star Colors A: Yellow B: Red

Discoverer STT 523

Notes

Companion is M1.

Separation over time

Measured 1851 → 2021 (170 y)

Separation drift 6.8" → 7.8" (+1.00")

Rate +0.0059" / y

PA drift 294° → 300° (+6°, +0.035°/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.