Hi,
Welcome to my collection of OB Association's.

When one talks of observing Deep-Sky objects, most amateurs tend to think of galaxies, nebulae, open and globular clusters at the top of their list. There is, however, a somewhat neglected category of Deep-Sky object that is overlooked by many amateurs. That is the "O-B Association".

An O-B Association is a large, very loose form of an open star Cluster consisting of young spectral type "O" and "B" stars. They cover large volumes of space, are loosely held together by gravity and have short lifetimes (a few million years) as a distinct object. While O-B Associations are considered a separate Deep-Sky category from open clusters, both types can be found together, with an open cluster forming the core region of a larger O-B Association. In time, the outlying O-B Association will drift apart, merging with the other field stars in the region, leaving the more gravitationally bound open cluster as a still observable object.

Perseus OB-1

Double Cluster - 11/10/2012 - 50mm Orion Refractor f3.2, StellaCam-II, 8 seconds

Very few star charts actually plot O-B Associations as objects. But many can be found in "SKY ATLAS 2000" and "URANOMETRIA" because of the number of their individual stars that are plotted. A good example of this is "PERSEUS OB3", found around Alpha Persei, and "ORION OB1-B", surrounding the "Belt" stars of Orion. Because of their large size O-B Associations, are best observed with binoculars or small telescopes at low powers.

Orion OB-1C

M42 Region - 11/10/2012 - 50mm Orion Refractor f3.2, StellaCam-II, 8 seconds

The following charts show the location of some of the best O-B Associations that are visible in small scopes or binoculars. Also included with each chart is a sketch of individual objects to give you an idea of what to expect. All sketches were made with an 80mm refractor spotting scope using low-power eyepieces, with an amici prism giving a corrected field of view.

If you wish to read more about "O-B Associations", try the following sources:


- "IN PURSUIT OF O-B ASSOCIATIONS" SKY & TELESCOPE JAN 1986
- BURNHAM'S CELESTIAL HANDBOOK
- WEBB SOCIETY DEEP-SKY OBSERVERS HANDBOOK       # 3 OPEN AND GLOBULAR CLUSTERS
- THE NIGHT SKY OBSERVERS GUIDE and the OBSERVER'S GUIDE magazines
- THE MILKY-WAY BY BART BOK

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To view the location and sketches of OB Associations, select from the finder charts below:

ORION	Sketch - 80mm Refractor f3 & 32mm, (10x) 01/29/1993
	ORION OB-1A
Sketch - 80mm Refractor f3 & 32mm, (10x) 01/20/1993	Sketch - 80mm Refractor f3 & 32mm, (10x) 01/20/1993
ORION OB-1B	ORION OB-1C
Sketch - 80mm Refractor f3 & 16mm +2.8x Barlow, (59x) 01/20/1993
ORION OB-1D

PERSEUS	Sketch - 80mm Refractor f3 & 8mm, (41x) 10/13/1987
	PERSEUS OB-1
Sketch - 80mm Refractor f3 & 32mm, (10x) 10/24/1993	Sketch - 80mm Refractor f3 & 28mm, (11x) 10/13/1987
PERSEUS OB-2	PERSEUS OB-3

AURIGA	Sketch - 80mm Refractor f3 & 32mm, (10x) 01/23/1990
	AURIGA OB-1 & 2

GEMINI	Sketch - 80mm Refractor f3 & 32mm, (10X) 01/23/1990
	GEMINI OB-1

CASSIOPEIA	Sketch - 80mm Refractor f3 & 24mm, (14x) 10/14/1993
	CASSIOPEIA OB-1
Sketch - 80mm Refractor f3 & 24mm, (14x) 10/24/1993	Sketch - 80mm Refractor f3 & 24mm, (14x) 10/14/1993
CASSIOPEIA OB-6	CASSIOPEIA OB-14

SCUTUM	Sketch - 80mm Refractor f3 & 32mm, (10x) 09/06/1993
	SCUTUM OB-1

VULPECULA	Sketch - 80mm Refractor f3 & 32mm, (10x) 09/05/1993
	VULPECULA OB-1

CEPHEUS	Sketch - 80mm Refractor f3 & 24mm, (14x) 09/05/1993
	CEPHEUS OB-2

CYGNUS	Sketch - 80mm Refractor f3 & 32mm, (10x) 09/06/1993
	CYGNUS OB-1
Sketch - 80mm Refractor f3 & 24mm, (14x) 09/05/1993	Sketch - 80mm Refractor f3 & 32mm, (10x) 09/06/1993
CYGNUS OB-2	CYGNUS OB-3
Sketch - 80mm Refractor f3 & 32mm, (10x) 09/05/1993
CYGNUS OB-9

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You may E-MAIL me at:lsmch@comcast.net
This is it. Hope you enjoyed the visit. Come again soon!

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