Rare to get two grazes worth travelling to in one night. Even rarer to get two cresent moon grazes on 6th magnitude or brighter stars in one evening, just a few miles apart. And rarest of all - on opposite dark limbs! This requires the moon's vector and the Earth's rotation vector to be projecting in such a way to insure rapid rotation of the graze point, so that the cusp angle can change rapidly. These conditions all converged on the evening of January 15, 2013. Derek Breit, Walt Morgan, and I all took note. Rick Baldridge was also on board, but his balky car was more seriously ill than he'd thought, and wasn't cleared for launch on graze day. So he reluctantly bailed at the last minute. I had this pair on my Events list for some time, and the skies looked to be clear. I contacted Becky, who was eager to join on her second graze, and this time to be an observer gathering data. I spent two evenings working on planning locations and running OCCULT4 and Google Earth to find the perfect spots for Becky and I. 6.3 magnitude ZC 3444 would graze the southern limb at the end of twilight, 2 degrees from the southern cusp, and then 4.9 magnitude Kappa Piscium would graze the northern limb of the moon 4 degrees from the cusp 2 and a half hours later. The cusp angle would have to rotate fully 6 degrees in that brief period.

As we got close, weather promised to be clear, and Derek Breit and Walt Morgan took note independently and sent out an email. It's always more fun and more valuable when you can get together with friends and do these grazes and asteroid occultations, so I suggested to Becky that we all meet and do these grazes where the paths were relatively close - in the Gilroy/Morgan Hill area. Becky was really excited about observing and getting timing data on her first grazes. She'd accompanied me on the Oct 26 '12 graze in Bonny Doon, but this one she'd be taking her own data by voice/WWV radio/tape recorder method.

First graze, of 6.3 magnitude ZC 3444 through Aromas and Gilroy, CA at 6:30pm. The graze is only 2.2 deg from the southern cusp and the profile has only 2 steep mountains whose right sides near the summits will probably be sunlit. 3 maybe 4 timings.

PreGraze Meeting Spot; Frazier Lake and Shore Road, SE corner. Depart for stations by 5:30pm.

Two big mountains dominate the profile. The larger one was very sunlit, as expected. The one on the left was just barely lit, and much dimmer than the V=6.3 star; OK to try and get graze timings on.

Derek produced the Kaguya profile from Gilroy/Morgan Hill area. Central Graze: 2:33:45UT

Station 1: at the end of the measuring yellow line. Becky was farthest north, ~100 yds north of me (station 2), on the dirt road towards the big barn. At 2.2km north, take Hwy 25 south a couple miles from 101, past the creek, onto this quiet road

I rushed around in the afternoon - a 3 mile run on the beach, then packed gear at home, then off to InShape for a short swim, then to the observatory to pack the scopes and rest of the gear, then to Becky's in Aromas, then jump on 101 and up to the meeting site on Frazier Lake Rd and Shore Rd in the ag fields south of Gilroy.

Me, Derek, Becky, and Walt at the meeting site just after sunset. We're anticipating some very nice grazes.

Under the cresent moon - Walt and I confirm station assignments

My standard graze setup - the 10" Meade LX200 classic, PC164C with Bumgarner mod for manual gain control, downstream of a Meade f/3.3 reducer.

At Becky's station. She's bundled against the wind and cold.

My old Magellan GPS logged geodetic coordinates at my site.

I got onto our dirt road, just 2 miles from the meeting site, and drove down about 300 yards to Becky's station and offloaded the 8" Meade, timing equipment, and suggested she get the station up going and then I'd run down in about 15 minutes after getting my station up. She got the WWV radio working, polar aligned the scope, verified the star and the correct cusp, practiced with my mini-cassette tape recorder, and discovered that there was no power from the 9V battery I gave her for the scope. When I returned after my own initial set up about 100 yards north of her, I brought the VOM tester and sure enough - the battery had only 1.5V, not the 9V advertised;. it was DEAD! So, she'd have to use the slo-mo control to keep the moon and star in view. Meanwhile, at my station I had my own troubles after getting everything up and running. The star was beautifully set off against the cresent and earthlit dark side (see title picture at top)... but with 3 minutes before the onset of the graze, the telescope froze up. No tracking, no response from the hand paddle. Darn Meade electronics! Too late to restart and get in another 2-star alignment, so I flipped the power off/on and it came back up, and I simply used the hand paddle every few seconds to reposition the star, while insuring the bright cresent didn't sit on top of the time stamp. It all worked fine, and I got the whole graze successfully recorded. Becky and I both had 4 events from the two big mountains.

Meeting Site After Each Graze - In Morgan Hill: the Taco Bell at the corner of Condit and E. Dunn, just off the Hwy 101 in Morgan Hill a couple of miles south of the graze sites for the second graze.

Taco Bell Meeting site

It's OK - Taco Bell is healthier than just about any fast sit-down "restaurant", and there's a million of 'em

Logging reaction times and other data while it's fresh in our minds.

Taco Bell Grazers - We continued on to the post-graze meeting site in Morgan Hill, the Taco Bell on East Dunn.

Walt shows off his 4" digital monitor. I was impressed how much easier it made finding dim stars vs the LCD display on my camcorder. He has a small company that now sells these, so I bought one, on the spot.

Derek generated an on-the-spot Kaguya profile for our second graze. This was the better event - a 4.9 star on the dark limb with lots of small scale features. He plotted each of our chosen tracks, and confirmed we had good coverage of the best spots.


Second graze - at 9:06pm; 4.9 magnitude Kappa Piscium grazes the north limb 4 deg from the cusp, but at an altitude of only 10 degrees. Looks like a good profile at 0.9mi south. Here's the predictions. Getting a good horizon is critical.

Central Graze: 5:06:21 UT for our Coyote Creek Park site.

Kaguya Profile for Kappa Psc graze


Becky and I took the tracks 0.90mi South of the 400ft TANZ corrected limit line, and we set Becky up at 0.95mi South, in the parking lot for Coyote Creek Park, off Burnett Ave.

To get to the site: Cochrane exit southwest to Monterrey Blvd, turn right to Burnett, take it right, over the freeway to the end, parking lot and our site.

Are we gonna really pull this off? We worried about the cold damp conditions now at 9pm giving rise to corrector plate dew. Or perhaps more telescope trouble.

But it all went famously. My 10" scope didn't choke this time, and no dew or other trouble. We were on opposite sides of the same parking lot, yet we had different grazes. I had 25 events, Becky had 14 events.

Walt was a few hundred yards further north of Becky and I, on another road. Got 10 events. We met back at the Taco Bell and here we synchronize the camcorders and play them back in synch, to see which mountains and valleys differed between our sites.

On playback, I realized I'd forgotten to check/replace the batteries in the tape recorder. It taped fine early on, but by the midway of the second (very cold) graze, the batteries were clearly suffering, as Becky sounded like she was on helium, and the second ticks were racing by. Will take some additional effort to reduce them. My own video recording is beautiful! I should try and download it and make a compressed .avi and post to YouTube. 25 D's and R's in the space of 2 minutes on an Earthlit moon is a visual treat.

The data reductions are here.