Here is my vision of a "standard configuration", but there are any number of telescopes that can be used. You need enough aperture to do the job correctly. I recommend either a Celestron 8 or Meade 8 telescope. It must track so you don't have to push it by hand. The telescope should be mounted using a wedge and tripod (not shown) and have the capability to be powered from a battery, preferably a cigarette lighter plug that lets you get automobile power or portable 12VDC long life battery that can be recharged as required. This view shows a C8, the right angle finder and a right angle eyepiece for optical timing of an occultation. A finder scope is mandatory and it must be boresighted with the telescope BEFORE the night of the occultation. "Boresighted" means when you look through the finder and center it on an object, it appears also in the telescope eyepiece. The finder should be able to be focused clearly and locked in place with small screws as in the figure below. You can easily do that during the day time. A right angle finder is preferred to make high elevation occultation target stars easier to locate.
The limiting magnitude under clear skies of this setup with a PC164 camera is around +12 magnitude.
For dew prevention, I recommend a dew cap and Dew Zapper available from Orion Telscopes. The Dew Zapper is powered from a cigarette lighter plug. Alternatively you can use a portable hair dryer but this requires a lot of power and may not be as convenient as a Dew Zapper. The Dew Zapper wraps around the metal tube just below the corrector plate while the dew cap sits on the edge of the telescope and is held in place by Velcro.
If you are using both of the above and powering them via the cigarette lighter of an automobile, you can use a y-plug available from Radio Shack (shown below). A car battery can run the C8 clock drive for hours without impact to the car battery and a drive corrector makes that possible (shown in lower right portion of next photo).
You must polar align the C8. If using a tripod/wedge, it is also useful to have a door stop or fulcrum so you can tilt the tripod leg facing north to get the north star in the center of your finder without having to keep adjusting the wedge to the right latitude.
Wide angle binoculars are useful in locating the field before you proceed further. Use star charts provided through Steve Preston's OCCULTATION PREDICTION SITE. There are 4 levels: wide angle, 5 degree, 2 degree and 30 arc minutes. Fixating on the wrong star is always a possibility. Confirm for sure you are looking at the correct star by verifying the presence of other key star groups to the north/south/east and west of what you think is the correct target star using the 2 degree chart.
Have several eyepices available when locating the star field. If you plan to visually time it rather than using video, also have a right angle viewer. Be sure to use good quality eyepieces! I suggest a combination of 32mm, 24mm and 12mm. (not shown) Visual timing must be recorded on tape, preferably a portable battery powered one with a microcassette tape. (not shown)
To get your precise geographical position, a GPS receiver is recommended. It will typically have an accuracy of 3m. Record your latitude and longitude in degrees, minutes, seconds and tenths of seconds. Altitude is normally not necessary. Almost any model is acceptable.
Other equipment can be very helpful: a compass, inclinometer and a set of Allen wrenches. All can be found at hardware stores. The compass can be used in daylight to help point the mount to true north, while the inclinometer can be used to tilt your scope to the correct latitude. Allen wrenches are vital for many things such as loosening the wedge, securing the wedge to the tripod, etc.
The most economical and sensitive TV camera is a black and white model PC164 available from SUPERCIRCUITS. in Austin, Texas. This camera can reach 12th magnitude under good sky conditions. Moonlight, twilight, sky conditions can all impact the ability for faint star detection. To attach it to the C8 or M8, use a T to C adapter available from many telescope dealers.
The PC164 is a tiny, lightweight, and sensitive plug and play device and must be powered by 12V. The black chord connects to 12VDC, the yellow BNC connector is the video OUT chord. You can also obtain a 12V battery and charger system from SUPERCIRCUITS.
Next you need a VCR, also preferably portable battery powered. A camcorder is ideal, but choose the camcorder carefully to ensure it will take an RCA plug for VIDEO IN recording. SONY makes a wide variety of camcorders and many of them have the ability to record from an external camera. Below you can see how the RCA jack connects from the PC164 into the Sony camcorder.
To record your voice and time signals you can get a lapel microphone (upper right part of photo below) also from SUPERCIRCUITS.. Then you can power both PC64 and microphone using a Y-chord from the same 12V battery. This chord is also available from SUPERCIRCUITS.. The camcorder should use HI-8 or 8mm tape though at some point we should transition to a more long lived medium such as DVD. Be sure that the camcorder has a pullout display screen or you are somehow able to route the video into an external monitor of some sort. Most camcorder view screens of 2.5 inches in diameter are sufficient to get a decent focus and verify you are on the correct star. The photo below shows the video system and microphone where both the PC164 and mike are powered jointly by it, while the camcorder has its own internal battery. Follow the chords. The battery chord goes to the base chord of the y-cable. The one part of the y-cable leads to the lapel mike, the other leads to the video camera. But the video camera comes with a BNC connector(female). You need another chord with a BNC connector (male) on one end and an RCA jack on the other. You may have to buy a chord with RCA jacks on both ends, then a separate male BNC connector that will simply slip on to one RCA jack to make this all work. The power chord of the video camera connects to the other part of the y-cable while the RCA jack takes the video signal from the video camera into the camcorder.
Time signals must be recorded through the camcorder audio channel. Use a short wave radio battery powered that can receive 5.0, 10.0 and 15.0 MHz. You need three frequencies to account for changing atmospheric conditions. Get a radio that is digital and not one that you are required to tune using a hand-turned knob. You can typically find short wave radios at Radio Shack and some boat supply dealers.
A rat's nest of wires can result from this configuration; so you must ensure that most of the parts are contained in a briefcase and set on a table about the same height as wedge. Use twist-ties to keep the wires from getting tangled in the dark. You should endeavor to sit during the observation and be able to have ready access to the slow motion controls on the telescope in order to make minor adjustments to keep the star centered in the field of view. Try to keep at least 2 other stars in the field in order to detect seeing or transparency impacts as well as a reference in case clouds drift through.
Rotate the camera on the T to C adapter so that the resultant field of view in the camcorder display screen matches the star chart.
Keep the star focused at all times. Focus can change unpredictably. Avoid having to make tracking adjustments during the minute preceding and following predicted central time of occultation. This can be assisted by ensuring the mount is aligned to the pole properly and the motor is tracking well. Since the PC164 camera is lightweight, there is no need for counterweighting the telescope.
I use a camera lens instead of a telescope and my preference is for Nikon but any removable camera lens will work. For the example here, all that is needed is
a) a tripod
b) the PC164 video camera
c) a Nikon telephone lens (here is shown a 75-150mm f/3.5 zoom lens). A zoom is good because you can change the field size based on the brightness of the star.
d) a c-mount adapter for Nikon lenses
I don't want to repeat the instructions for getting power to the camera and the video signal into the camcorder, so see the above section for that data. You will need the camcorder, lapel microphone, RCA to BNC chord, y-cable, 12V gel cel battery.
The lens to choose is based on your sky and the brightness of the target star. It pays to try two or three lenses to make the optimal decision.
In the first photo the components are laid out of the floor before assembly.
Here they are tripod mounted. The PC164 has 1/4-inch 20 threads/inch adapter which fits the standard tripod. You may want to use regular or lock washers if needed to get a tighter connection.
Ideally, you should have two of everything. That is usually not possible, so as a backup plan you should go 'visual' if a critical component in the video recording chain causes an unrecoverable failure. At a minimum I recommend two 12V batteries, two microcassette tapes (for tape recorder), two video cassettes.
The following is detailed information that you can use to train yourself and others in organizing for an asteroid occultation.
O-7 days (where "O" means occultation): email or phone alert issued/IOTA web site is updated. This update might also come even closer to the date of the occultation.
O-7 days to O-1 day: locate the target star. Practicing ahead of time is invaluable and can save the day. PRACTICE! If you are training others, finding the star before occultation night will be like an investment in success. There are many times when clouds are near the star on occultation night and locating it can consume lots of time. The star might be also be situated in an area of the sky devoid of other reference stars or it could be in a very rich area with confusing star patterns. Other factors such as proximity to the moon or twilight makes early detection very important.
O-1 day: determine where you plan to observe. If from your house, notify the local coordinator so we will know that that part of the occultation path is covered. Send either GPS coordinates or an address. If you plan to be mobile, also notify the coordinator so you can be assigned a site area.
O-2 hours: you should be set up at your chosen site by this time. Polar align your mount and be sure your clock drive is working. If using a Schmidt-Cassegrain watch out for dew formation. Use a ‘dew zapper’ or portable hair dryer to mitigate this possibility. Be sure you have the following: at least 2 eyepieces (wide field), bug spray, right angle finder, red flashlight, binoculars, copies of the star chart, tape recorder with fresh batteries and tape rewound to the beginning, short wave radio source of time signals. This latter item is the key to precision timing.
O-30 minutes: find the target star; observe from a comfortable position either sitting or standing that will not cramp your neck. Be sure your hands are free as possible.
O-20 minutes: test your voice and the radio and recorder to be sure the time signals and your voice evenly record. Play back to verify. If one is drowned out, reposition and repeat the test until you get it right. Be prepared to comment on passage of clouds, distractions, seeing changes, stability of the target star, etc. during your 10 minute observation window. Be quick about it and be aware to quickly call out when the star disappears and reappears. Use either "D" and "R" or "out" and "back".
O-5 minutes: begin continuous observing. Start radio and recorder (or video). If the radio fades in and out, another person at your site could assist in helping get the signals back.
O+5 minutes: end observation. Turn off radio and recorder (or video).
O+1 day: within 24 hours report positive or negative observation to your coordinator. Provide your name, exact location of site, telescope info and duration of any event(s) seen.
O+3 days: fill out the report form ans send it to the occultation organizer.
The following is a list of possible excuses as to why observers failed to see an occultation when otherwise, they should have been successful. They are based on my personal experiences:
did not find the star prior to the night of the occultation
misidenitifed the target star
used someone elses telescope with which they were unfamiliar
did not use a telescope with a clock drive
had a battery failure associated with portable short wave radio, tape recorder, or video system
Schmidt-Cassegrain telescope dewed over because it was left out too long and too far ahead of occultation without being covered
eyepiece being used either had too high or too low magnification
no finder on telescope or the finder was useless in helping to locate key stars
finder and telescope were not collimated
a key screw or wrench was not present when assembling the telescope
polar alignment not successful because Pole not visible and no compass was available.
tape recorder ran out of tape
radio drifted off frequency and no time signals were recorded
lights from police car or other approaching cars blinded observer at key time
observer was held at bay by armed person when trespassing without permission on private property in the middle of the night
vibrations from passing trucks shook instrument
seeing conditions were so poor that image of target was not stable enough to ascertain an occultation
temperature so cold that observer could not concentrate for long period due to inadequate clothing
jacket held over observer and eyepiece to keep out nearby lights caused fogging of eyepiece due to temperature/humidity combination
dark adaption lost due to not using a red flash flight
telescope tripod shifted due to being set up on unstable ground
observer lost concentration due to being set upon by hordes of mosquitoes and not having repellant
star fainter than predicted and observer confused
observer unsure of occultation because depth of drop was less than one magnitude
tape recording failed to record observer's voice because time signals were too loud and no test was done before hand to ascertain equal level of recording between voice and radio
occultation not seen because observer was talking to people at the site and not paying attention; lost track of time
telescope aperture inadquate to see a star that dim
too large a scope used and target star could not be properly confirmed
"GO TO" telescope computer would not work and observer had no experience using the telescope to manually star hop to the target star. Excessive dependence on technology!
image intensifier battery failed and no spare was available
occultation occurred at too low an altitude and it was not possible to find the star in enough time
occultation occurred in too bright sky and this was not anticipated before the observer attempted the event
Please pay attention to the above pitfalls and you will likely never have to worry about failure again.
The best way for amateur astronomers to map an asteroid topography is to enlist the aid of a group of likeminded individuals who are willing to engage in an organized effort to time the event from equally spaced locations perpendicular to the path of the asteroid shadow. Since the path is known to within a certain level of accuracy (e.g. plus or minus 1.0 path widths or less), the idea is to first choose an event with the least error in minor axis. Assuming there are just 3 observers the best strategy for this case is have an observer at the center, one 1/2 path width north of center, and the third 1/2 path width south. I first described this strategy in articles in the early 1980's.
If you have 10 observers, for example, you might distribute them at equal distances north and south of the center so that each observer has no chance of duplicating another's observation. This strategy breaks down when groups in differernt US states try to observe. In many cases, observers might have fixed locations that make it impossible to move; other observers have restrictions on the distance they can travel based on personal and other commitments.
The ground based effort, primarily by amateur astronomers, continues to make strides in improving our knowledge of the asteroid population. Equipment used has varied from small telescopes and tape recorders (employed to record disappearance and reappearance information) to video cameras and image intensifiers. This is an excellent application of scientific field work that either an individual or an astronomical society can undertake. Since most stars occulted by asteroids are between +9 and +12 magnitude, it is necessary to develop the necessary skill to locate relatively dim stars, or else to have a telescope that is capable of navigating to a set of coordinates using computer input. Still, you need to be able to interpret the orientation of a star chart, a finder eyepiece, and a telescope eyepiece effectively due to inversion of optics which will show the star field in a different aspect from that shown on the star chart. It is sometimes easy to locate the wrong star, so double checking the target star by "star hopping" to it from more than one key star is a good aid in assuring you have not misidentified the target. The E.A.O.N. web site contains star maps and also updated information in the days prior to the occultation that will assist observers in knowing possibly where the predicted path has shifted. Serious observers should check this site several times a week prior to the occultation event. But, what if you look for an occultation and end up seeing nothing? There is a high value in obtaining a 'negative observation'. It will actually be of benefit in confirming where the occultation did NOT take place. This can be especially useful in the case where the path is not known with any degree of certainty. Even if the path is well understood and you are predicted to be in the path and do not see any occultation, this negative data is extremely vital to the assessment or confirmation of other observations of either the primary occultation or a secondary event (meaning possible evidence of a satellite).
A typical timeline to observe an occultation might start out like this. Assume an event is predicted to occur at 9:04pm CST (03:04UT). You should plan to be at your observation site 2 hours before. This is necessary in order to maintain flexibility in case of changing weather patterns. Your location should already have been known by IOTA prior to the observation in order to preclude duplicate observations by people located too close together geographically. If not, be sure you know the latitude, longitude from GPS or from a good topographic map. If in extreme situations, time is running out and you are trying to outrun a cloud system, set up anywhere and worry about locating your exact site later on.
In humid areas, users of Schmidt-Cassegrain telescopes should expect fogging of the corrector and use a 'dew zapper' or hair dryer or dew shield. Success is enhanced if you have located the star at the same time of night at least a day or two before the event. Be sure you have assembled all of your equipment in their exact configuration at least a day before the occultation. Leaving one critical piece of gear behind, such as a tape, microphone, adapter, eyepiece, or power chord can be very devastating. Using a telescope with a clock drive will allow you to keep your eyes focused on the occultation instead of having to manually track the star. If observing from a fixed site, be sure the star will not be masked by houses, trees or other obstructions at occultation time.
On the night of the example occultation above you should locate the target star to be occulted no later than 30 minutes before the event. Begin observing nonstop from 9:02pm to 9:06pm; that is the predicted time +/- 2 minutes. Why such a long interval? To account for possible time errors in the prediction and also to search for satellite companions of the asteroid as well as to establish atmospheric seeing effects. For visual observers maintaining such a vigil can be quite a challenge to avoid eye fatigue. Hence using a video system conquers this problem since the video can record without error all during this period. It can also be replayed for analysis. The clear disadvantage to human observations is that there is no second chance and the observation cannot be visually replayed. There are also such things as human reaction times, possible seeing effects which may or may not be related to the occultation process. All of these are overcome by using video. At completion of the occultation, packing up is usually done within 30 minutes after the event.
Successful audio or video tapes should then be copied and sent to IOTA for analysis. The observer should always maintain the original unless requested otherwise. Again, I want to stress that if you DO NOT observe the occultation but you have watched during the key time, your observation is VERY important. It is critical to know where the boundaries of observation are located in order to establish upper limits on the prediction error and also the size of the asteroid. All observations made whether positve or negative should always be reported using the form on the IOTA website. Immediately after the event, send an email or notify your local coordinator of what you saw or did not see.
Mobile observers should exercise extreme care to drive safely to/from the site. Sometimes it may take extra time to locate a site which will eat into the setup time. Remember it is better to be safe than to take unnecessary risks with your own safety or those with you. Choose a site that is out of the way and free of lights and obstructions. Be sure it is not on private property without the owner’s permission. Notify the local police if that is feasible. Why? Many an observer has had a police car pull up moments before the occultation and this thwarted what might have otherwise been a successful event! Also it will possibly mitigate any phone calls from passers by reporting unseemly behavior along the roadside. If you pick and site and then have bad feelings about it, listen to yourself and find another safer location. Check out the site for presence of hazards such as barking dogs, fire ants, muddy ground, high tension lines, holes, other animal presence, barbed wire, and being illuminated by oncoming headlights. If it is windy, look for a wind break or set up your scope behind your vehicle. Always try to take another person with you for security purposes. Never carry a lot of money and bring a cell phone if possible. Carry a copy of the asteroid alert email, identification, and anything else that might prove to police that you are out there doing astronomical research.