Occultation of a 9.1 star by Bettina

Nov 27/28, 2020 at 12:17:38am from Santa Cruz

Preston Predictions

Bright star and a "sure thing" from Santa Cruz. The only problem, it's straight overhead at 88 degrees altitude. The field will rotate strongly during the half hour before the occultation, moving from the eastern half of the sky to the western half. Passes within 1 degree of zenith about 15 min before the event. This event requires the 1.25" diagonal configuration for both eyepiece and Watec setup.

plotted for 12:00:00am

Results:

Frustrating! Neither I nor Kirk got any data, despite clear skies and plenty of time available for set up, and a bright star. It was the over-head location. This star passed within 1 degree of the zenith during the 10 minutes prior to the event. Neither Kirk nor I followed my earlier advice of tipping the mount so that the singularity in the mount coordinate system was offset from the alt/az singularity at the zenith. The 8SE scopes have a hard time tracking near the zenith, and constant and rapid drift foiled me. I did get the target star in the eyepiece field, but by the time I got the Watec swapped in and focused, the field was unrecognizable. The rapid rotation of the field also mean one couldn't count on recognizing star patterns, and this foiled Kirk. He never ID'd the target star.

Solutions:

(1) Kirk verified that if the scope is pushed as far forward in the dovetail mount as possible, then the 2" diagonal will clear the mount base, and therefore we can still use our 2" Q70 32mm eyepiece with the large 1.1 degree FOV. This helps a lot in identifying the star fields. Then, we swap in the 1.25" to 2" adapter and then the Watec (but, is there a clamp screw to hold it firmly??)

(2) I strongly recommend that we tip the mount by shortening one of the legs; the leg that will most insure the mount singularity is never close to the star before the event. We need to insure the star is at least 10 degrees away from the mount singularity until after the event. So it will be important to know the trajectory of the target before the event, so we can rely on minimal rotation and decent tracking.