Why are some fairly bright stars not labelled?
All stars with visual magnitude less than 7.00 should be labelled. However, photographic film is more sensitive to blue light than human eyesight. Thus, a blue star that appears fairly bright might in fact have a magnitude greater than 7.00 and thus not be labelled. There are some cases where a faint red star is labelled, but a nearby brighter blue star is not. If these stars were viewed in the sky by a human observer, the blue star would actually appear duller. 3.7. How closely spaced are the grid lines in the chart annotation? The “heavier” dotted lines are spaced 5 degrees apart (which is 20 minutes of right ascension); the lighter lines are spaced 1 degree apart (4 minutes of right ascension). 4. Errata 4.1. Why do some annotations appear below the horizon or behind land objects? The annotations are created using a mathematical model which doesn’t take account of the horizon (or objects near the horizon, such as mountains, buildings, trees, etc), so some stars are annotated even th
