"Developed for Netscape."
Last revised: 12-01-1997.
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
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.
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 OBSERVER'S GUIDE MAGAZINE
- THE MILKY-WAY BY BART BOK
To view the location and sketches of OB Associations,
select from the finder charts below:
You may E-MAIL me at:firstname.lastname@example.org
go to: Top of Page:
go to: Larry's Deep-Sky Sketches:
This is it. Hope you enjoyed the visit. Come again soon!