Soon after the developement of photoelectric observations, the UBV
photographic photometric extended the capabilities of
photometry to observe fainter stars to make deep studies of
clusters or cover a wide area. It represents a corpus of 100'000 observations.
However, plates measurement techniques and
a often limited number of plates in each colour result in lower precision.
The errors on magnitudes and colours are generally of the order of 0.05 mag
or larger. This produces the scatter observed in colour-magnitude diagrams
based on photographic data. Photographic photometry is now largely replaced
by CCD photometry in most systems.
UBV photometry stored in the database is still useful to make a good stellar census
in the cluster areas and to prepare an observing campaign. Detailed studies of the
cluster CMDs require however better precision data.
|B-V||:||B-V colour index|
|U-B||:||U-B colour index|
List of clusters
Query the references
Last Update: 17 February 1998