When is the best time to observe RS Ophiuchi?

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

Where is RS Ophiuchi located in the sky?

RS Ophiuchi lies in the constellation Ophiuchus at right ascension 17h 50m and declination -06° 42′.

What telescope do I need to follow RS Ophiuchi?

To follow RS Ophiuchi through its full brightness cycle (magnitude 4.3 to 12.5) you need a telescope of roughly 180 mm or larger — the star fades out of smaller apertures near minimum light.

RS Ophiuchi — Variable Star in Ophiuchus

Observable Variable Star Showpiece (78/100)

Range: 4.3 - 12.5, Period: 453.6d, Type: NR+LB

VariableStar Ophiuchus (Oph) Visible

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1Physical Properties

Magnitude 4.30

Range 4.3 - 12.5

Period 454 days

Variable Type Recurrent Nova

Spectral Type Peculiar

2Position & Identifiers

RA 17h 50m 13.0s

Dec -06° 42' 28.0"

Constellation Ophiuchus (Oph)

HR 9129

Variable ID RS Oph

3How easy to follow?

Magnitude 4.3 – 12.5 mag Amplitude 8.2 mag Period 453.6 d Type NR+LB

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Equipment	Bortle 3	Bortle 4	Bortle 5
Naked eye Naked eye	Imp.	Imp.	Imp.
50 mm finder 50mm finder	Imp.	Imp.	Imp.
150 mm telescope 150mm scope	Hard+	Hard	V. hard+

Easy Medium Hard Very hard Impossible

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

To reach "Medium" at Bortle 3, you'd need at least a 180 mm reflector.

4Visibility

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Best season May – Jul (peak: Jun)

5Light Curve

6Comparison Stars for RS Oph (4.3–12.5)

Nearby stable stars for estimating brightness (AAVSO)

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8

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9

Spectral Classification

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

Variable Star

Recurrent Nova; Recurrent nova; Last eruption 2021

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.

Y Oph

Medium

Pulsating variable, period 17.1d

Variable Star mag 6.21 0.8° Ophiuchus

Tau Oph

HIP 88404; Tau Ophiuchi; 69 Ophiuchi

Hard+

Tight double — a rewarding split at 1.4″

Double Star mag 5.24 3.5° Ophiuchus

NGC 6517

Medium+

Globular cluster — dense ball of ancient stars

Globular Cluster mag 10.3 3.7° Ophiuchus

Collinder 350

Easy

Open cluster

Open Cluster mag 6.1 8.0° Ophiuchus

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