Note that the histogram shows relative proportions in each year, but that the years do not scale to each other because they represent different totals - ten times as many objects being observed in 1997 as were observed in 1925.
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Although database records may not actually be finalised in regard to numbers
of both objects and observations, the three selected years illustrate a change
of emphasis during more than a century of the BAAVSS observing programme.
Note that the histogram shows relative proportions in each year, but that the years do not scale to each other because they represent different totals - ten times as many objects being observed in 1997 as were observed in 1925. |
In 1925, 48 of the 57 variables were mira stars, 5 were semiregular, 3 were UGSS, and only one RCB (R Coronae Borealis itself) made up the programme. Before the formation of the BAA & the VSS, the great 19th century surveys initiated by Argelander found many variables as a by-product of mapping the sky. These discoveries started to undermine the entrenched idea that all stellar variation was extrinsic as in eclipsing binary stars like Algol. Hence the emphasis in the first decades of the VSS was on comparing observed lightcurves with calculated predictions to further the study of pulsating stars. Eclipsing Binary stars are dealt with in a separate programme by the VSS and the main database contains only a small number of EB observations.
By 1975 several mira stars had been dropped from the VSS programme but twice as many objects were under observation. Semiregulars were the largest group (47 stars) with eruptives of various type coming next. In fact, the histogram shows that more observations were accrued on the eruptives than on the SR variables. There was also interest in suspected variables as listed in the CSV and then later in the NSV. More binocular objects were under observation after the merging of the Binocular Sky Society (BSS) into the VSS.
At the start of the 1980's, the VSS records - all on paper - were reaching enormous proportions. At the same time, home computers were becoming available and a couple of attempts were made to transfer records into machine-readable form. This project was taken up again in 1991 and by 1997 a major part of the records were logged into the database. In addition to the transcription of existing records, modern electronic communications were being used to report current observations so that it was possible to deal with many more objects as shown in the histogram columns for 1997.
Eruptive stars are now the prime target with about 40% of the objects and well over half the observations. Note, though, that many eruptive variables (as in the Recurrent Objects Programme) can accrue disproportionate numbers of negative estimates in comparison to other types of variable where a lesser number of positive sightings is often ample to follow the light variations. Several Active Galactic Nuclei (AGN) are now under surveillance and SR variables are still popular. Mira star observations have increased again because, with less paper reports requiring lots of time and energy to deal with, there is no need to separate out priority groups to the same extent.
Some stars have been monitored almost continuously throughout the existence of the VSS. Mira itself (omicron Ceti) is on all three sky distribution diagrams (2h19m -3°) also R Hydrae (13h30m -23°). Observers will easily identify several other stars observed in all three sample years. The interesting RVb variable U Mon (7h31m -10°) has the first recorded database observation (1888) and has been observed every year since 1964, but apparently there are no extant section records on this star for the early part of the 20th century including 1925. International results reported via 'The Astronomer' organisation are included for 1997 accounting for the increased number of southern hemisphere objects.