Pre-point stars for the Sacramento, Calif. region
Pre-point stars for the Phoenix, AZ region
Pre-point stars for the Monterrey, N.L., Mexico region
Instructions and annotated charts to Pre-Point your scope
ZIP file for charts below
Prepoint charts for tonight’s (363) Padua occultation of 14 Cancri

On Sunday May 10th, at 10:16 pm MST, the asteroid (363) Padua will occult the 5.7-magnitude star 14 Cancri for likely less than 4 seconds for all throughout the greater Phoenix and Tucson areas. Many details of the event, including path maps and detailed charts, with labeled versions, to locate the target star directly are on the special page for the event at . The idea of pre-pointing for the occultation was discussed in my May 5th message:

“For many, just going directly to the target star and tracking it should work fine. 76 Geminorum, close to Pollux, provides a good pre-point opportunity 26 minutes before the occultation, and 3rd-mag. Mebsuta provides on an hour before that. But if your scope has a narrow field of view, you will need to use fainter stars near those bright stars, to pre-point your telescope accurately enough; the charts we will post later [now] will allow you to do that.”

The basic idea of prepointing is to point your telescope at the direction (altitude and azimuth) that the occultation will occur, then don’t move the telescope (turn off all tracking). Then the Earth’s rotation will carry the target star near the center of your telescope’s field of view at the time of the occultation. As long as your telescope field of view (FOV) is wide enough that it takes a star at least 30 seconds to drift across it when not tracking (that’s the case for all but the very largest, longest focal-length telescopes), then you can use the pre-point method. Just point your telescope at the prepoint line of declination shown on the charts, at the time indicated with the tick-marks along them, and your scope will then be prepointed. Another value of pre-pointing is that if you can see the pre-point line with your scope at the right time, then the view of the target will not be obstructed by trees or buildings. That can even be done naked-eye; if you can see Pollux at 9:50 pm MST (or specifically, the area a few deg. to the left of it), you can observe the occultation at that place.

The pre-point line drawn on the charts goes back 2.5 hours since any earlier than that, the sky will be too bright to observe the fainter stars, at least in Arizona (around Monterrey, Mexico, they could observe almost an hour earlier). The prepoint charts are prepared for the Phoenix region, but since the motion of the occultation shadow is so fast, they can be used for other places along the path, with the time corrections given below:

                                            Occultation             Time correction,
Area                                    Universal Time      seconds
Sacramento, Calif              5:15:55                   -25
s.w. Las Vegas, Nev          5:16:10                   -10
Phoenix, Ariz.                    5:16:20                     0
Tucson, Ariz.                      5:16:23                   +3
Monterrey, N.L.                  5:16:43                   +23

If you use a mighty mini, the drift-through time is 10 minutes, so the corrections above are negligible. Even for large telescopes with relatively small FOV’s, the correction for Tucson is negligible as the event duration, and time uncertainty, are about the same size.

A list of prepoint times and declination offsets for stars to mag. 10.0 near the path are here for the Phoenix region; it can also be used for Tucson (for them, add 3s to the times): ST363PHX.TXT
A similar list for the Sacramento, Calif. area is here:  ST363SMF.TXT
And one for Monterrey, N.L., Mexico is here: ST363MTY.TXT.
These lists include stars to mag. 10.0 within 5.0 arc minutes of the prepoint line, and stars brighter than mag. 6.0 out to about 30 arc minutes from the line.

The level 4 prepoint charts for Runcam mighty mini’s, in chronological order from earliest to last, are 4-1Padua.jpg, 4-2Padua.jpg, and 4ppPadua.jpg, in this .zip file. Venus is near the bottom left of 4-1Padua.jpg, just below 1.6-mag. El Nath.

The level 5 prepoint charts for small refractor systems (like 80mm “midi”s, but can be used with 120mm “maxi’s” that have smaller FOV’s, are, from earliest to last, are 5-1Padua.jpg, 5-2Padua.jpg, 5-3Padua.jpg, and 5ppPadua.jpg (which has the maxi FOV rather than midi), in this .zip file.

I don’t give pre-point charts for narrow FOV scopes like 8-in. SCT’s (too many of them) except for the 3 best pre-point opportunities, near Mekbuda, 76 Geminorum (76 Gem), and 2 Cancri. They are shown in the labeled-charts .pdf file, and in these unlabeled versions: 7PaduaMekbuda.jpg, 7Padua76Gem.jpg, and 7Padua2Cnc.jpg, in this .zip file.

The key prepoint charts are labeled in this .pdf file. PrepointCharts20200511Padua.pdf

Good luck with your observations - hope the clouds clear away, or at least are thin enough, for your observations!

David Dunham