Alpha Herculis (Rasalgethi / Struve 2140)

Sketch of Alpha Herculis (Rasalgethi/Struve 2140/STF 2140)

Sketch of Alpha Herculis (Rasalgethi/Struve 2140)

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Observation Notes:

Rasalgethi is a fantastic, colorful double. The bright primary shone a yellowish orange with–get ready for it–a sage green secondary. The diffraction pattern was captivating in better than normal seeing.

Subject Alpha Herculis (Rasalgethi / STF 2140 / ADS 10418)
Classification Double Star
Position (J2000)* Hercules [RA: 17 14 38.9 / Dec: +14 23 25.2]
Position Angle 111° [My Measurement 2009.3]
105° [WDS 2007]*
Separation 6″ [My Measurement 2009.3]
4.8″ [WDS 2007]*
Magnitudes* A: 3.5; B: 5.4
Spectral Types* A: M5Iab; B: F2V
Date/Time APR 5, 2009 – 3:45 AM (APR 5, 2008 – 10:45 UT)
Observing Loc. Flagstaff, AZ – Home
Instrument Orion SkyQuest XT8 Dobsonian (203 mm dia./1200 mm F/L)
Eyepieces/Mag. Pentax XW10 + 2X Barlow (240X)
Meade Astrometric EP + 2X Barlow (200X)
Conditions Clear, light breeze
Seeing 7/10 Pickering
Transparency Mag 5.5 NELM
*References The Washington Visual Double Star Catalog (Mason+ 2001-2009); Catalogue of Stellar Spectral Classifications (Skiff, 2009); SIMBAD

2 Replies to “Alpha Herculis (Rasalgethi / Struve 2140)”

  1. Spectacular!
    Wonderful job in drawing the diffractionrings.
    Have you drawn those digitally or by hand?

  2. Hi Harro, thank you. When I’m at the eyepiece, I first make a rough sketch of what the diffraction rings look like. You can see a basic example here: Double Star Log Sheet. For doubles that are separated by just a few arc seconds, I try to estimate how many diffraction ring radii separate them and note that on the rough sketch. That sample I linked to is an earlier set of drawings. Since then, I’ve tried to make a greater effort to portray the general nature of the flickering patterns in the rough drawing–showing the rings, arcs, speckles and diffraction spikes that the stars, scope and the atmosphere are portraying for me.
    After scanning the drawing, I use Photoshop to re-create what I roughly sketched using different paint brushes, layers, masks, and filters. I’ve experimented with a lot of different methods to try and display a snapshot of what I saw. It has gotten to be a little complex, so it takes a while to get each sketch processed and posted. I’ve still got a decent backlog of sketches I need to finish up.
    Thanks for asking the question,

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