The most complete enumeration of the lucid stars by magnitudes has been made by Pickering (‘Annals of the Harvard Observatory,’ Vol. XIV). The stars were classified by half magnitudes, calling
M. M. Mag. 2.0 all from 1.75 to 2.25 2.5 all from 2.25 to 2.75 etc., etc.
For the northern stars Pickering used the Harvard Photometry; for the southern, Gould’s ‘Uranometria Argentina.’ A zone from the equator to 30° south declination is common to both; for this zone I use Gould. The number of each class in the entire sky, north and south of the celestial equator, is as follows:
Northern Southern Hemisphere. Hemisphere. Pickering. Gould. Total.
1± 9 14 23 2.0 17 15 32 2.5 17 24 41 3.0 37 41 78 3.5 61 74 135 4.0 114 126 240 4.5 228 234 462 5.0 450 426 876 5.5 787 681 1,468 6.0 789 1,189 1,978 ----- ----- ----- Sum. 2,509 2,824 5,333
It would seem from this that the number of lucid stars in the southern celestial hemisphere is 315 greater than in the northern. But this arises wholly from a seemingly greater number of stars of magnitude 6. In the zone 0° to 30° S., Pickering has 214 stars of this class fewer than Gould. Hence it is not likely that there is any really greater richness of the southern sky.
The total number of lucid stars is thus found to be 5,333. But it is not likely that stars of magnitudes 6.1 and 6.2 should be included in this class, though this is done in the above table. From a careful study and comparison of the same data from Pickering and Gould, Schiaparelli enumerated the stars to magnitude 6.0. He found:
North pole to 30° S. 3,113 stars. 30° S. to south pole 1,190 stars. ----- Total lucid stars 4,303
For most purposes a classification by entire magnitudes is more instructive than one by half magnitudes. From the third magnitude downward we may assume that 40 per cent. of the stars of each half magnitude belong to the magnitude next above, and 60 per cent. to that next below. We thus find that of
Total. Mag. 0 and 1 there are 21 stars 21 Mag. 2 there are 52 stars 73 Mag. 3 there are 157 stars 230 Mag. 4 there are 506 stars 736 Mag. 5 there are 1,740 stars 2,476 Mag. 6 there are 5,171 stars 7,647
Here it is to be remarked that under magnitude 6 are included many other than the lucid stars, namely, all down to magnitude 6.4. The last column gives the entire number of stars down to each order of magnitude.