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Rho (ρ) Herculis and STT 329 (OΣ 329)

Rho (ρ) Herculis  (Σ 2161)  (H II 3 — AB only)          HIP: 85112    SAO: 66000
RA: 17h 23.7m   Dec: +37° 09′
Magnitudes   AB: 4.5, 5.4     AC: 4.5, 13,3
Separation    AB: 4.0″           AC: 118.5″
Position Angle   AB: 320°  (WDS 2010)    AC: 222°  (WDS 1998)
Distance: 402 Light Years
Stellar Classification: B9, A0

You’ll find Rho (ρ) Herculis located just to the east and slightly north of Pi (π) Herculis, which marks Hercules’ left (east) shoulder.  (Stellarium screen image with labels added – click on the chart for a larger view).

In my 76mm f/15.7 Tasco Rho (ρ) Herculis is a pair of of glowing white stars that leap out of the eyepiece at you.  At a mere 48x they are distinct, individual, gleaming globes, even though they seem to be barely touching one another.  With a change to a 9mm Meade Plössl (133x), I found two distinctly separate white globes of light, with the smaller and fainter of the pair still parked close to the primary.   I also had a good view of them in a 102mm refractor at 55x, which showed a very tight but distinctly split pair of white stars,  and a 127mm refractor provided a similar, but brighter, view at 59x.

There’s a thirteenth magnitude companion — out of reach the night I was looking for it — lying two arc minutes in the distance, and there may be another one, Aa, but no definite information exists at this time on it.   There’s a small treasure trove of information to be found on Jim Kaler’s web site for this dazzling white duo.

East and west reversed to match the view in a refractor, click in the sketch for a larger view.

STT 329   (OΣ 329)
HIP: 85181 
SAO: 66014
RA: 17h 24.5m
Dec: +36° 57′
Magnitudes: 6.35, 9.9
Separation:  33.1″
Position Angle: 13°  (WDS 2007)
Distance:  684 LY
Stellar Classification: G5, F0

If you haven’t noticed it yet, just to the east of Rho (ρ) at a distance of about fifteen arc minutes is STT 329 (OΣ 329).  If you move Rho to the northwest corner of your eyepiece, you should see both pairs of stars in the same field, as shown in the sketch.  The 6.3 magnitude primary is shadowed to the north by a much fainter 9.9 magnitude star.  Both were easily visible in the 102mm and 127mm refractors at 55x and 59x, respectively.  Using a 20mm eyepiece for 60x in the 76mm refractor, I was able to see the fainter companion easily with averted vision.  I saw the primary as white in all three scopes.

The best view here is with a low power eyepiece — you want to get both pairs of stars comfortably situated in the field of view in order to feel the full impact of the view.


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