At 14:03 4/6/00 -0400, Bill J. Gray wrote:

>Hi folks,
>
>MISSING STARS:
>
> Most people only notice the missing strip of GSC stars in Hercules.
>(If you go to a 20-degree field of view, then center on the star
>68 Herculis, then use "Extras... Toggle User-Added Datasets" and
>turn the "GSC Plates" dataset On,
> _________________
>| |
>| ( ) Missing area
>| |
>| GSC plate N158 |
>| |
>|

* Capella |

>|_________________|
>

Bill's diagram came put looking a bit funny on my screen, but his
explanation is correct(as usual).
The cause of the Opposite star is due to internal reflections inside the
Oschen Schmidt camera.

The first and second magnitude stars are so bright that the image on the
photographic plate is reflected back onto the corrector and refocused
exactly opposite the center of the plate from the star image. It is
slightly out of focus and makes a spot about one inch in diameter on the
plate. You can see through these images on the POSS prints and there are
many stars there but I am sure that the automatic measuring machines had
problems with many of them.
As bill suggests, turn on the POSS plate overlay. Go to one of the bright
stars. Then click on a location exactly across the center of the plate
area and you will find one of these dark areas.

This group never ceases to amaze me with discoveries. Good work!