The Lunar Rover
If you have been paying attention lately, you have heard me making a lot of noise about a grazing occultation of Aldebaran. First magnitude star grazes are pretty uncommon, so this one was worth some effort. The bad news was that it would require a trip to West Virginia or Pennsylvania to see. In the end, we did mount an expedition, got good data, met some great people and had a fabulous time. Below is the rest of the story.
Grazing occultations occur when the moon tangentially approaches a star. The non-smooth features on the moon's northern or southern limb cause the star's light to flicker in and out. The exact behavior of the star's light is unpredictable because our knowledge of the geography of the moon's polar regions is inexact. That makes it fun to observe grazes and worthwhile to take data on what we observe - we can help fill in some of those gaps. Even if you don't take data, watching a graze gives a sense of the moon's motion like no other phenomenon I have observed. Sitting at the eyepiece at high power, you see the star drawing ever closer to the moon. In the case of a dark limb graze, you cannot usually see the limb. So you never know quite when the star will begin to be occulted. If you observe with a Dob like I do, you also get a strong sense of the Earth's motion as well as you repeatedly tug on the telescope to keep the field in view.
Observing a graze is an exercise in high drama (OK, so it is not bungee jumping...) Grazes take a lot of planning because they take place over a geographically very limited area. You never know what the weather will bring. You never know what the exact nature of the graze will be. And, of course, you never know what the observing gods will choose to do to you to test your character. This one is particularly frustrating - you always ask yourself what else could go wrong that you haven' t thought of. But those observing gods are very resourceful. They always can come up with a new wrinkle to toss at you. One veteran grazer I met told me that he has been watching grazes for 20 years, and no two are ever the same. I've seen far fewer, but I'll drink to that.
Aldebaran is the brightest star (other than the sun) which can be occulted by the moon. And the September 12 graze was the last visible from the eastern US until 2015. The path of this graze ran from coastal Maine to south central Pennsylvania, northern West Virginia, central Kentucky, near Nashville, and on to the Big Bend coast of Texas. In planning this graze, I immediately thought of West Virginia. The path of the graze crossed I-77 near Ripley, WV. Examination of maps revealed that this was a pretty hard area to observe from. To take graze data, you need a firm geographical datum such as an intersection or well marked landmark to gauge your position. We saw little possibility of this near Ripley. So we looked elsewhere. The graze passed near Huntington, WV, on the Ohio River. This was a longer trip, but the presence of communities near the path was more promising.
It is always difficult selecting graze sites in locales where you are not familiar. I think that West Virginia qualified. Luckily, Phil Creed made a fine suggestion - contact an astronomy club in the area. So, I found the Ohio Valley Astronomical Society located in Huntington. I emailed their contact, Jeffrey Ball and explained our dilemma and asked if he and his club would be interested in helping us out. His initial email back was cautious but promising. But he followed it up soon after with a much more enthusiastic response. He had done a little digging on The Sky and understood a little better what was involved. He felt it would be fun, and he could rouse some interest in the club.
At this point (late June, I believe) I dropped the ball. Phil Creed pointed out to me that Huntington would be prone to river fog. So I started thinking of elsewhere, or of passing on the graze entirely. But Jeff was persistent and emailed me in early August. We started corresponding again. He bought some topo maps and I sent him coordinates. As the date approached, I was leaving the details to Jeff. We had four people interested in the trip - John Waechter, Kent Rothermel, Tom Kolar and myself. Eventually, Tom dropped out leaving three. I was becoming blasé and apprehensive about the trip, although the weather looked promising.
At this point, fate intervened in the person of David Dunham. Although I have never met Dunham, I have spoken to him several times around graze times. He is the founder and President of IOTA, the International Occultation Timing Association. He is an experienced graze observer and professional astronomer. David was aware of our plans because I submitted them to him earlier and was on a list of graze expeditions for this event. David called me Wednesday evening and suggested that he might observe with us in Huntington. He was on his way to Nashville for the annual meeting of IOTA and originally planned to observe there. But if the weather was bad, he might stop and observe with us. Then he told me of the other two grazes. Yes, there were more.
I was aware that there were three grazes that morning as the moon traversed the Hyades, but had not really looked at them in the Huntington area. Dunham told me that all three were well placed for easy accomplishment of a grazing "hat trick". He faxed me some maps, etc. and set the hook. Until this point, I had left the planning to Jeff in WV. But, with these additional grazes, I knew that I would have to get a hold of maps and plot them out. Luckily the Kent State map library is convenient to me at work, and a good way for me to copy maps. I brought the maps home and plotted all 3 grazes out on Thursday evening. To my amazement, the last two paths converged near the town of Ardel. If we found a good spot, we could observe both without moving!
I spoke with Jeff and told him of the additional grazes. He sounded a little shell-shocked, but recovered nicely. We moved up our meeting time to allow us to get there in time for the early graze. I received phone calls on Friday at work from Dunham (it looked like Huntington was a go because Nashville was being shrouded by clouds form tropical storm Frances). Also, Gerry Samolyk from Milwaukee called and made arrangements to meet us.
We met at John's house Friday evening, and stuffed our stuff in John & Donna's nice van. We departed about 6:30 and arrived at the rendezvous point about 10:30 - a little early. As we sat in the van in the parking lot of Hills, we saw a pickup truck pull in with an equatorial mount strapped in place with bungee cords. Must be an astronomer. Actually, two! Eventually, we met Jeff Ball, Dave Richards, Mark Angle, Larry Oyster, and Dave Tolley. And, Gerry Samolyk from Wisconsin, an experienced grazer. Dunham had been there earlier, talked with Jeff and left his maps with us. He then left for western Kentucky - closer to his eventual destination of Nashville.
The first graze was ZC 680, a 6.7 magnitude close double star (0.1 arcsec). The graze path passed through Ashland, KY, just up the road from Huntington. We selected some possible sites from the map - near the Ohio River. The moon would be quite low here, only about 13 degrees up at graze time, so we needed a good horizon. We gathered at an Ashland station and Jeff and I took a reconnaissance trip up the road and picked some sites in the "sweet spot" recommended by Dunham. (Note - although we are trying to do some science here, we also want to see something interesting. So we typically try to place observers so that all will see multiple events,) We spread out and set up in three groups. Kent, John and I set up close together since all our stuff was stuffed together in the van. Our site was only about 15 feet from US 23, a well-traveled truck route. Also several trains passed by us. Ashland is a heavily industrialized town, and WWV radio reception was poor due to interference. These problems could have been dealt with by choosing a different site. But here is where the observing gods threw us a curve. When I looked at the scope, I saw a bright star approaching the moon. Something didn't quite seem right. But I didn't worry about it. A few minutes later, I noticed a fainter star nearer the moon. This was ZC 680. I ended up mentioning it to Kent, but not to John. Unfortunately, John didn't catch the problem until it was too late. Our observing companions from WV also were suckered.
This was a difficult graze. The low altitude seemed to cause flickereing. I wasn't sure if it was due to the double star nature, or seeing. I got some data, but lost some in the middle because of fogging of my eyepiece. As it turned out, Gerry had problems as well with his video setup and radio. After the graze, we met back at the Ashland again.
Aldebaran would be grazed farther south. We traveled through Lavalette along Rt. 152, around a hairpin curve just above the tiny burg of Ardel. Just past the hairpin, we found an old general store. We pulled off and tried to figure out where we were. In order to get to the "sweet spot" for both upcoming grazes, we would have to be a little farther south. Jeff & I went back north on the road (yes, north - remember the 180 degree hairpin). Jeff suggested we go down into a park called the Huntington Police Farm Park. The main gate was locked, but there was a second entrance. We drove down into the park and found an ideal area we could all set up. The only risk was being confronted about being there. (I kept thinking about the "police farm" part). We agreed the risk was acceptable, and retrieved our group. We drove down and set up. I kept hearing dogs and imagining the caretaker waking up... Paranoia is a wonderful thing.
The Aldebaran graze was at 3:23 a.m. We were all set up and ready. But again, the observing gods were plotting. The moon has no atmosphere. When a star hits the limb, it should disappear immediately - there is no atmosphere to refract or absorb its light and cause it to fade. But fade, it did. A couple times. It surprised me so much that I'm sure I hosed up my data. We all noticed it, and Gerry's tape clearly showed it. It even showed a fade at the end after it came back from the long occultation. Also, the gods gave us more events than we expected from the profile plots.
After the spectacular Aldebaran experience, we relived it several times via Gerry's tape. Most of the WV folks left, except for Jeff. After Aldebaran, the third graze was going to be a let down - the 8.3 mag. SAO 94056 at about 5:20 a.m. We all rested a little and ate some. When I emerged from John's van at about 5:00, I looked at the moon's oft-grazed limb and saw, with difficulty, our quarry, It appeared that this one would be tough. John saw it with his 8". Kent had real problems with the C-5 he was using. He wandered off and started talking with Jeff. But as the star approached the dark limb. It became easier to see. In fact, for John and I, this was probably the cleanest of the three grazes - no flicker or fade. Just multiple events. Unfortunately, Kent and Jeff talked through the start of the graze. I suspect that Kent could have seen the star against the dark limb. Gerry reported that his tape showed the star. I'm not convinced. But the gods rewarded our persistence.
Afterward, we packed up. Gerry decided to go back to the luxurious Red Roof Inn and get some sleep. Jeff went to breakfast with us. We then drove back home, arriving about 11:30 a.m. It should be noted that I had observed a local graze near home at 4:30 on Friday morning for 4 grazes in 25 hours. Unfortunately, the observing gods taught me a lesson about recording a graze with my recorder in the "pause" mode. They also taught me about checking my altitude axis on my scope after rotating my tube. You'd think that sooner or later they would run out of things to teach me...
What an experience! Three grazes in 5 1/2 hours. Four grazes
in 25 hours. New friends made. New memories.