O B   A s s o c i a t i o n ' s  


            created: 02-16-1997.             revised: 02-25-2013.

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

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



You may E-MAIL me at:lsmch@comcast.net

This is it. Hope you enjoyed the visit. Come again soon!