4. What equipment is best to record an asteroid occultation ?

        VIDEO SETUP is the preferred setup since it does not involve human error in estimating the exact time of the  

          disappearance and reappearance of the star. My portable video setup is described here.  Steve Preston has a technique

          for reducing video timings here.  Paul Maley describes a comprehensive video setup for observers who desire to reach

          11-12 magnitude stars here.

                  Portable Video setup using 4" motor driven Meade telescope, PC-164C video camera and Collins I3

                  intensifier on car trunk. Shown also (lower right corner) is Camcorder and shortwave radio. Notice "rock"

                  on tripod leg to maintain balance.  This entire mobile setup weighs just 26 pounds and fits in a backpack.   

          VIDEO CAMERA: I highly recommend the highly sensitive black and white camera PC-164C from

          www.supercircuits.com, (1-800-335-9777). It retails for $129.95 and is one of the most sensitive cameras on the market

          today. It was reviewed with several other low light video cameras in the February 2003 SKY AND TELESCOPE

          magazine page 57.    

        VISUAL TIMINGS:  If you don't have a video setup, you can perform the occultation with a small telescope, tape

        recorder (or digital voice recorder), and a shortwave radio. The procedure to record the occultation this way is very

          simple:

            1. Locate the target star and track it during the 5 minute window surrounding the occultation.

            2. Tune in your shortwave radio to either 5, 10 or 15 Mhz (this is radio station W W V out of Ft. Collins, Colorado)

            3. Start your recorder at least 3 minutes prior to the predicted time of the occultation and make sure it can be heard in

                 the recorder.

            4. When you see the target star dim/vanish, yell "D" , and when you see the target star reappear, yell "R" into the

                 recorder.

                                 "D" stands for disappearance, "R" for reappearance.

                Continue to record and watch the target star for a possible second occultation (by an asteroid moon) for 2-3 more

                minutes.

             5. Note your location by estimating the distance and direction from the nearest intersection. Draw a diagram if needed

                 of your  location. Use this information  to get your latitude and longitude from www.MapsOnUs.com.  Or use one

                 of the many low cost Global Positioning Satellite (GPS) receivers to determine your latitude, longitude and

                 elevation. Elevations from USGS Topographic maps can be obtained at www.topozone.com.

              6. Analyze your recording, and try to extract your "D" and "R" times to 0.2 second or as accurate as you

                   can. Techniques to do this can be found here.

              7. Submit your successful occultation, location and "D" and "R" times to your local coordinator   

                   and if you have a miss, submit your data also. REMEMBER: A "miss" observation is very

                   important to place size limitations on the asteroid !! See chord # 2 above on the Lindemannia event.

       Go here is a list of asteroid occultations I have successfully observed as principal observer.

       Each of my successful asteroid occultations  was the result of numerous failures. The failures are the result of   a number  of reasons - weather conditions, equipment problems, path shifts of the asteroid's shadow, and local surprises.

5. Problems in observing asteroid (and lunar) occultations

WEATHER CONDITIONS can move in at the last minute, or the converse can be true - bad weather doesn't clear as predicted.  During an attempt of the occultation of  the asteroid 911 Agamemnon in March, 2000, haze moved in after I located the target star in my telescope, and within about 1 minute just before the occultation, the haze thickened to the point that I could not see the star about to be occulted. As it turned out, I was right in the path of the occultation !! 

For the spectacular occultation by 828 Lindemannia over the Houston area on November 10, 2002, over 100 observers were recruited by Paul Maley and myself in the Houston and San Antonio area. The weather forecasts were very good with clear skies predicted. Fog rolled in and never cleared for all but 12 of the observers. I was one of the lucky ones. I was situated near the northern path limit near Giddings, Texas and had clear skies and video recorded the occultation. Paul Maley was situated just 4 miles south of me and he had fog roll in just 5 minutes before the occultation occurred ! Within minutes after I video recorded the occultation, fog rolled in and covered up the clear sky I had.  

EQUIPMENT PROBLEMS. This is nothing new. When traveling to observe an occultation equipment can fail at any time for a number of reasons. Always bring fresh new batteries to operate your video, telescope motor drive, short wave radio and other equipment. Don't take a chance with batteries that are even slightly used.  Several times I have had low battery power in cold weather which impaired he function of my video equipment. These batteries seemed fine when I tested them at room temperature prior to leaving, but later failed at the critical moments. New batteries will delay the effects of cold weather.

More on equipment.... See Paul Maley's (IOTA Vice-President) web site on basic equipment setup and tips on observing. 

PATH SHIFTS.  The prediction of the exact path of the asteroid's shadow on the ground (Figure 1 above) is not perfect. The prediction of an asteroid occultation depends on the accuracy of the stars position and the accuracy of the asteroid's orbit. The highly accurate modern star catalogues give IOTA astronomers star positions with unprecedented precision.  The asteroid's position is another story. Although highly accurate asteroid positions are provided to IOTA astronomers by  Lowell Observatory and the U.S. Naval Observatory, errors of up to 1 full path width of the asteroid are possible. It's not easy to predict the position of a piece of rock in space that is on the average between  150 million and 300 million miles from Earth. This means that if the asteroid's ground path width is 100 km, then the uncertainty could be as high as 100km, which means the actual path of the asteroid's shadow on the ground could be off by 100km. This is why observers are actively sought that are situated outside the predicted north and south limits of the paths.  Asteroid occultations are a team effort and fixed site observers and mobile observers need to coordinate to provide the maximum coverage in case of shifts in the paths. 

LOCAL SURPRISES. Now you have your telescope, recorder, new batteries and the sky is clear. So looks like you'll have a successful occultation, right?  As described above, the path could shift substantially, causing you to have a miss.  If your set up just off the side of a road, car headlights could distract you and/or hinder your night vision. Even with a video setup, passing cars could cause light reflections on your video causing the target star to momentarily fade in and out. Use a dew cap over the end of the telescope tube to block passing car headlights. Curious passing cars will stop and ask what your doing and ask if you need help. Just tell them briefly your making a sensitive observation and wish not to be disturbed. Nearby property owners can make a scene and cause major disturbances (and they have every right to know what your doing) foiling your efforts.  Some nearby property owners will call the Police/Sheriff and you'll soon be visited by the Law and have to explain why your standing around in the dark with some unfamiliar equipment "pointing" somewhere.  IMPORTANT: If a property owner or the Police insist that you leave, DO SO RIGHT AWAY. Your safety is more important than the occultation. 

If possible, it is advisable to contact the local authorities, Police, Sheriff, etc. to advise them of your planned observations and location ahead of time. This will 90% of the time prevent surprise visits. This is not always possible when your traveling seeking a site for an asteroid event since your site is usually unknown until you get there and pick one.  

For the occultation of by 283  Emma on January 10, 2000, I was setup for about 1 hour on what appeared to be a deserted road late at night. I was keyed up, since 3 hours earlier I successfully timed the occultation of 208 Polyxo. I was now seeking  2 occultations in one night. Everything was going well, I had the target star, the recorder and shortwave radio were going, and I was anxiously watching the star field.  Within only 30 seconds of the occultation, a Police car drove up with his bright headlights on. My night vision was ruined and I lost sight of the target star. It took some convincing to have the Officer turn off his headlights, but it was too late. The occultation was over and my night vision was gone.  You may want to have a small sign at your setup stating your goal, so as to notify cars driving up to turn off their lights. If your doing a visual observation and a diesel engine vehicle drives up, you have a sound problem, and this could drown out your voice and W W V  shortwave recording  (this has happened to me). 

 6. How to find out about the next occultation over your area

 IOTA maintains a web page by astronomer Steve Preston that lists all upcoming asteroid events worldwide here.  Global and regional charts show the predicted path over land, the uncertainty (estimated path shift error), time of the event and a detailed minute by minute location of the asteroid's shadow on the ground plus data on the target star being occulted. It is highly advised that if you plan on observing and recording an asteroid occultation, that you coordinate with other observers so as not to duplicate chords. IOTA has a discussion group here for observers to communicate/coordinate on asteroid and lunar occultations,  techniques and other time critical occultation related topics.   

  7. How to report an asteroid occultation observation

  The reporting of your successful asteroid occultation or "miss" observation can be made by use of a on-line form or by emailing a special format text file. The on-line report form located here unfortunately works only with a Netscape browser. A sample text file form of a recent occultation appears here. If for some reason you cannot use the on-line form or the text file then send the following information to IOTA President David Dunham at dunham@erols.com :

   1. Your latitude and longitude and elevation and how it was determined. (GPS, www.MapsOnUs.com, USGS Maps, etc.)

   2. The "D" and "R" times of the occultation event to at least an accuracy of 0.5 second or better.

   3. Mention if the "D" and "R" were instantaneous or gradual.

   4. The equipment you used including whether it was a visual or video observation.

   5. The time source used (WWV, CHU and the frequency).

   6. Whether or not you recorded/saw any secondary events (possible asteroid moon).

   7. Any other matter that affected your observation (weather, nearby lights, distractions, etc.)

 8. Useful Occultation links:

IOTA Asteroid Occultation Page. This page includes predictions of asteroid occultations for the current quarter. Has useful easy to read finder charts including date, time, with occultation paths plotted across the North America. 

Steve Preston's Asteroid Occultation Path Updates.  IOTA astronomer Steve Preston produces high quality path updates for upcoming asteroid events across the world. Steve uses the latest astrometry and the best star positions available to update the asteroid's paths in a comprehensive manner. The updates have maps showing the paths, describe everything about the target star, asteroid, magnitudes, and estimated duration of the occultation, plus detailed latitude/longitude points for plotting the path on a road/street atlas.

Paul Maley's Occultation Pages. From his over 35 years of experience in observing occultations, IOTA Vice President and astronomer Paul Maley has so much useful information on occultation observing, and many tips on visual and video equipment techniques,  plus advice on coordinating events in your area. His web page is a MUST READ !!

List of Asteroid Moons. This list of confirmed asteroid moons and suspected asteroid moons shows how much more research is needed in this area. With over 250,000 known asteroids,  there are only 75 known/ suspected asteroid moons. This is one reason why you need to get in on this exciting field for potential discovery.   

European Occultation Page. This comprehensive page, maintained by Eric Frappa, has predictions, maps and results for asteroid occultations for European Observers.

Derek Breit's Occultation pages. Derek Breit compiles extensive station lists for those  planning on  observing asteroid occultations.   

Sky and Telescope Magazine's introduction to Occultations.

Sky and Telescope Magazine's Planetary Occultations.

Doug Mink's Occultation Page and how the occultation technique was used to discover the rings of Uranus.

Robert Sandy's Occultation page and a list of upcoming lunar grazes and asteroid occultations.

Astronomy Today:  For more about asteroid events and solar eclipses, see my interview.

Asteroid profiles from recent occultations. Recent asteroid size/shape profiles from successful occultations over Texas.

Each profile includes the story direct from the observers, and how they made the observations.   

IOTA discussion group. This discussion group has much useful information on upcoming occultation events, and is how observers coordinate with each other for asteroid and lunar grazing occultations. Topics include telescopes, occultation techniques and equipment, video and visual timings, software, using GPS receivers, etc.                                                                             

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