More on Saturday Evening's Nephele Occultation
New 2002 October 29This is a message to George Roberts in response to his message about the Nephele Occultation to the list of the Amateur Telescope Makers of Boston, copied to them and to other observers in Massachusetts and New Hampshire. But the information is mostly general, useful for observers throughout the Nephele path. George, Thanks for your good advice to the ATMoB list; you're right that we want as good a spread as possible of observations from many locations across the path (like you say, if more than two people go to the ATMoB observing site, it will be a waste). Video observations are preferred for this (and any asteroidal) event, and should be attempted like you describe if a camcorder is available (maybe borrow a neighbor's if you don't have one?) but carefully- made visual timings are of value, too (best with a cheap tape recorder, WITHOUT voice activation, than with a stopwatch. If observers have trouble getting a source for WWV (or CHU) short-wave time signals, an alternative is the $30 Cat. #63-964 radio-controlled (by WWVB) travel alarm clock from Radio Shack; start recording 2 or 3 minutes before the event, after having set the alarm on the clock to go off 1 to 2 minutes before the event; the first alarm sound will accurately mark the start of the minute. After the occultation, keep the recorder going, and reset the alarm for a minute in the future, to get another good time mark after the event, so the tape rate can be determined. Another possibility is if someone records a strong local AM or FM station along with WWV to create a master tape, anyone in the area can use that local station as a time base, recording it from a car or transistor radio. Fresnel diffraction at the distance of Nephele will make the disappearance and reappearance appear gradual, taking 0.2 second or so; this effect is spread over a distance of about 200 meters. So the observing location does not need to be known to a few feet; an accuracy of even 50 feet is good enough. That can be determined after the fact with either a simple GPS receiver (preferred) or careful measurement of a 1:24,000-scale topographic map (you can print parts of them from topozone.com). Finally, the target star is a spectroscopic binary that was resolved during a lunar grazing occultation videorecorded in Japan in 2001. Those observations indicate that the component separation is likely to be of the order of half the angular diameter of Nephele, so the events will occur in steps perhaps a couple of seconds apart. Some observers will probably see only one component occulted, meaning that the star will appear to fade suddenly by 0.7 mag. or so, which should be quite noticeable with such a bright star, unless the seeing is really bad. Carefully note what you see! Since the duplicity means there's a good chance that more than 2 events will occur, stopwatches are not recommended for real-time timing; it's better to use a tape recorder, and even better a camcorder, or VCR and video camera (like those from Supercircuits) attached to your telescope. I also want to know in advance the locations of as many fixed- site observers as possible so that we can target the several mobile observers for this event to effectively fill in the coverage gaps. For this purpose, approximate long./lat., such as those that can be found at mapsonus.com (with your street address, get the map, then select map clicking will "show long./lat.") or similar sites. Good luck with your observations! David At 02:21 PM 10/28/2002 -0500, you wrote: > > WWV? It may be a newbie question.. so please excuse. I'm an AAVSO > >Estimating magnitudes isn't important (but because of the star's duplicity, an approximate estimate is of some value; it will be measured accurately by those of us who videorecord the event). > - stopwatch isn't good enough unless >you happen to be at a location that just misses the asteroid and reporting >that >nothing happened can be very useful.