The Astronomical League's
DOUBLE STAR CLUB

•  Description

• Every double star you try is not splitable. Better relax in your living room while reading a book, visit your friends or initiate more productive tasks.

• Only the most open doubles are splitable with difficulty. Almost no diffraction rings. The sensation is like "looking up from the bottom of  a swimming pool". Probably, your new refractor is having its first lights after two weeks of clouds. Same recommendations as for classification 0 apply here.
• Pickering-1: Star image is usually about twice the diameter of the third diffraction ring (if the ring could be seen).

•  Seeing very similar like observing from inside your living-room in winter without waiting for thermal equilibrium. 3 stars in the Trapezium are resolved at 40x during few seconds. Delta Orionis is observed as a double without problems.
• Pickering-2: Image occasionally twice the diamteter of the third ring.

•  It's difficult to use more than 50x, but every really open double is splitable. This is the minimum level you can expect to start double star observing. Maybe a bit boring for some people, but at least you can observe some traces of coloration on the components. If after some time of doubles observation you resign and start to hunt for faint-fuzzies, then this is the more suitable classification that night.
• Pickering-3: Image about the same diameter as the third ring and brighter at the center.

•  Observing coloration in double-star components is easy, but Epsilon Lyrae is not splitable yet.
•  Pickering-4: The central disk often visible; arcs of diffraction rings sometimes seen.

• Trapezium easy at 40x consistently, but using more than 100x is a nightmare. Epsilon Lyrae starts to split during very short periods of time.
• Pickering-5: Disk always visible; arcs frequently seen.

• Epsilon Lyrae is splitable almost 100% of time. Anyway, you can use 28x per inch of aperture with your telescope. This is the minimum recommended level to start making serious double star observing. You can measure separations and position angles using a reticled eyepiece and remain observing doubles along all the observing session.
• Pickering-6: Disk always visible; short arcs constantly seen.

• Epsilon Lyrae easily splittable. You don't feel tired of observe the beautiful diffraction rings on Castor while the time goes by. You feel your observing session is really productive and your Barlow lens brings out from your pocket.
• Pickering-7: Disk sometimes sharply defined; rings seen as long arcs or complete circles.

• Using a solar glass filter you can perfectly observe granularity on the Sun's surface with a good 4" aperture achromatic refractor. Easy to go up to 50x per inch of aperture using a refractor. Epsilon Lyrae splits using 60x with this observing instrument and Antares splits at 250x when located only 18 degrees over the horizon. You don't hear your wife/husband when she/he calls you because she/he doesn't find the TV remote control.
• Pickering-8: Disk always sharply defined; rings as long arcs or complete but in motion

• This is the same as 10, but the seeing is not stable at all and comes and goes, sometimes downing to 8.
• Pickering-9: Inner ring stationary. Outer rings momentarily stationary.

• Perfect Airy disk with textbook diffraction rings. Rules of maximum theoretical magnification break. Good achromatic refractors able to take up to 75x per inch of aperture. Apo and fluorite refractors reach 100x per inch of aperture or even a bit more. This condition is stable.
• You stay at telescope several hours but the time doesn't go by for you and you feel tempted to start crying when the first lights from the rising Sun come.
• Pickering-10: Complete diffraction pattern is stationary.

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