OBSERVING MINOR PLANET OCCULTATIONS IN ARIZONA ON THE ROAD

(based on personal experience by Paul D. Maley from 2016 forwards)

Real scientific work can be accomplished by sometimes never leaving home or by driving one way several hours distant. Ideally an occultation will fall over the location of the observer and no travel will be necessary. This is not always the case. For occultations of stars by minor planets the paths of these events may traverse any and all parts of the state. In Arizona, there is typically a high percentage of clear nights where the sky tends to be somewhat if not entirely cloud free. However, the highways leave something to be desired in terms of accessing certain parts of the state for astronomical purposes. The map below does not show all the challenges but defines the state boundaries. In some instances occultation paths will cross those boundaries. It is generally not advisable to travel into Mexico so that portion is eliminated for setting up observing locations. There are two major highways to the east, I-40 and I-10. Depending on where one lives travel via interstate highways is the fastest way to go from one place to another. However, areas in green indicate boreal forest and do not reflect the poor roads as well as mountainous areas where driving can be treacherous and very slow. Outside the yellow interstate highways all other areas may feature state or county roads or no roads at all. The latter cause the biggest concern for driving.

Arizona map with state boundaries in both solid lines at the southern border with Mexico and dotted lines with other states. Arizona is 400 miles long and 310 miles wide. The telescope symbol represents my usual location.

Observers can use a software tool OCCULTWATCHER which will permit views in both map form and satellite form. It is not always possible to use either in this tool to gauge elevations of a particular place. Lower elevations may feature hotter temperatures and denser atmosphere. Higher elevations, the reverse. Thus preparing to travel to a specific area requires preplanning to be sure that the observer has the right clothing. It can be well over 100 deg F from Phoenix to the southwest and simultaneously close to freezing in the far north of the state.

The map above shows the 3 interstate highways (I-40, I-8, and I-10) that run east to west and the two north-south interstates (I-17 and I-19). Observers should avoid the north east quadrant and east central section which offers roads of lesser quality and lower speed limits. Speed limits on interstates is 75mph and on state highways typically 65mph.

Planning for travel requires accessing a number of weather forecast sites. Some use the same weather model while others a different one. It can be challenging to decide on which forecast model is the correct one and may also entail real time monitoring of satellite images to see where clouds are actually developing, moving, and hopefully dissipating. Perhaps the most important element is the wind direction and wind speed at the predicted time of occultation. If one does not use a high profile vehicle one has to plan for wind buffeting the telescope. My vehicle is small and sometimes I can use its profile to block the wind; at other times I use a large hand held piece of cardboard held in a way as to block as much wind as practical. If the wind is too strong I attempt to find a structure or terrain that might do the same. In the Navajo Nation northeast of Flagstaff I actually drove into a river bottom and used the sides of the river to block direct wind impact, for example. In other cases I have looked for new home development areas which features walled communities. I try to find a wall that will block the wind from the proper direction. In many communities there are street lights and so a wall located near such a light must generally not be considered. In other new communities under construction it may be easier to find a temporary site where no lights have even been turned on. The image below illustrates such a development near Casa Grande, AZ. It is now unusable due to homes having been constructed and occupied and street lights introduced.

Using a wall from a community under construction in western Phoenix to block the wind. However, if manual polar alignment is required one must be able to see down to elevation 30 deg above azimuth 0 deg.

PLANNING FOR AN EVENT

The prediction for an example event is shown below. The “rank” shows this to be the highest rated event (100) so this would be a good occultation for which to plan. The straight line distance is about 86 miles and magnitude 11.6. It is easily within the ability of a 8-inch telescope and video system to record. The Moon is below the horizon and sun altitude sufficiently low to where the sky is reasonably dark. The elevation is quite low at 14 degrees. However, under good conditions, this is possible to record, but it is not ideal.

OCCULTWATCHER predictions for June 22 showing the Burgundia occultation.

CONSIDERATIONS BEFORE MAKING A COMMITMENT

Before committing to a particular occultation it is vital to examine the conditions of the occultation: cloud cover forecast; time relative to sunrise/sunset; presence and phase of the Moon; distance one is willing to travel; day of the week and time of night; prospective amount of time (IF ANY) that must be devoted to travel to/from the occultation; ranking of the occultation; magnitude of the star; change in magnitude during occultation; length of the occultation; telescope used; camera used; integration required of the camera in order to adequately capture the occultation and reduce the data; if a light shield is required; wind speed and direction.

If significant travel is needed then cloud movement and wind speed/direction become the considerations of highest priority. Having a high profile vehicle is beneficial to serve as a wind break if winds are 10mph or higher.

My vehicle is low profile and I use a large stiff piece of cardboard that I hold up after starting my recording to assist in wind blocking. This has served me well in the past 6 years. If possible, avoid wind at all costs. If there is an existing structure that can be used to block the wind such as a wall surrounding a home development, then use it so all attention can be focused on viewing the laptop screen during the occultation. Should winds be in excess of 15mph it is advisable not to commit especially if much higher gusts are involved.

Cardboard windbreak (left) that I use with the Celestron 8 telescope next to it

A decision not to proceed because of specific event characteristics might occur under any one of these conditions: star magnitude is too faint to produce a high signal to noise ratio, the elevation of the star is too low (perhaps 10-14 deg or less), the azimuth is in the direction of a major city light bubble that produces a very high background for the camera, the duration of the occultation is too short (below 1.0 seconds), the magnitude drop is too small (below 0.2), the Moon phase is too high and the star too close, the occultation is too close to twilight and there is not enough time to get pointed, cloud cover forecast is too iffy, temperature too cold to effectively operate equipment, site location too close to a major populated area or too close to a roadway where the observer’s site can be seen or telescope illuminated, site chosen is in an unsafe location, occultation ranking is below 100.

If wildfires are present in the state and prevailing winds have pushed smoke into the proposed site area, the obscuration may be too high to afford a good recording. Also some roads may be closed should fires be in progress and there is only one route to the site passing through such an area.

If all of these checks have been made, then proceed. However, one should always have the expectation that ‘what can go wrong will go wrong’ in mind. I have experienced a number of cases where the site I choose did not experience an occultation even one that was ranked 100. The VTI device could experience a failure that prevents GPS time from updating; a battery could fail at the worst time when there is either not a spare battery available or there is not enough time to change it out; the telescope is accidentally bumped in the dark causing the target star to be forced out of the field of view when there is not enough time to recover; the laptop could freeze; the device that takes the video and compresses it into the laptop fails; the observer forgets to start (or stop) the recording; the star is too faint to properly record the occultation (fainter than predicted); the predicted path was in error (this could happen even with a recent date pedigree); wind speed is too great to block or overcome and the occultation cannot be recorded; the police show up and train their car lights directly into your telescope at occultation time (why a light shield helps); tribal police show up and order you off the site with not enough time to move to a different location away from tribal land. All of the above have happened to me.

SAFETY RECOMMENDATIONS BEFORE TAKING OFF FOR AN OCCULTATION

Here are some common suggestions that will assist observers before they travel within or outside Arizona for a minor planet occultation. Carry the following in your vehicle:

enough water in case you are stranded for several days
a cell phone (or better yet a satellite phone)
clothing appropriate to predicted high and low temperatures for the areas in which you are traveling
a spare tire in your vehicle; some new vehicles do not have spare tires as standard equipment
inspect tires to be sure they are in good condition
emergency aid kit to include antiseptic, bandages, etc.
subscription to AAA or other emergency towing
at least 2 flashlights; one red flashlight for occultation work
extra batteries to power occultation equipment
light shield
any medication in case your vehicle should break down
maps of the local area if you do not have a built in GPS in your vehicle or can obtain cell service; a closeup map of roads and populated places of the area where you intend to observe the occultation
red triangles or other safety markers if your car breaks down on the highway; insure your vehicle is pulled off the road far enough to avoid being hit by other vehicles
CB radio for emergency communications backup
camera and / or dash cam in case you have an accident and need photographic documentation
license/registration/insurance for your vehicle
a companion if possible to travel with you
toilet paper
wet wipes
small shovel
garden cutting tool in case it is necessary to cut limbs preventing you from viewing a particular part of the sky
while it is not practical to carry anti-venom, know what to do in case of snake bite and be prepared to call for help
insure all tires are in good shape and at the correct tire pressure
insure that air conditioner, emergency flashers and headlights are operative
if you do not have a companion, insure that someone knows where you are going, when you might be back (at the latest) and your planned route
recommended highway speed should be 5 miles below the speed limit unless you are running late; be aware that some highways are 2-lane and passing can be hazardous
have more than one route in case the planned primary route to the destination is blocked as a result of an accident
if possible, carry a backup of each piece of occultation hardware: telescope, laptop, camera, IOTA-VTI and corresponding batteries
carry tools necessary to fix loose telescope or other hardware connections

An observer needs to give serious thought about the chances of being stranded in a location where communication is not possible before committing to a travel experience. Travel for an occultation could involve a total trip time on the order of 6 to 12 hours or even forced overnights in hotels (if available).

On a map it may appear that most of Arizona is covered by tribal land (Bureau of Indian Affairs), forest service land, areas blocked for access by the DOD, Fish and Wildlife, National Park Service and Bureau of Reclamation. This is outside of private property held by others. There are many places close to heavily traveled highways that may on inspection appear to be good observing sites; but you may find out that they are on tribal land or land controlled by others. If so, you must have permission from the local tribal council/institution to set up on these areas. That is also the case with other no trespassing areas. Not all accessible spots have signs. Even with this said, I have never had trouble finding a desert site for nighttime observation. Tribal police do patrol reservation/community areas at night and trespassers are subject to arrest.

At night, because of the chance of fatal accidents, if you see a car/truck parked on the side of the road for any reason try to avoid driving past in the lane closest to the shoulder where that vehicle is stopped. Move to the next lane before passing that location.

SELECTING A SITE

The map below can be used at different scales in order to choose an observation site. It has the option to show the map view (below) or a satellite image view. The pegman option permits dragging the icon to a particular location and examining street views as required. Observers should consider forecasts when traveling to know which part of the path will have the best opportunity to observe the occultation. This could mean traveling 150-200 miles each way with the state. Once a location has been selected using a tool like mapquest.com can assist in planning the journey in order to gauge the amount of travel time. The map below is an example of a case where only 3 observers have signed up and so choosing alternate sites is easy.

OCCULTWATCHER provides the above map of possible places where this event can be seen. The prediction shows the path between the two blue parallel lines with the heavier red lines defining the 1 sigma path error and fainter red line the 2 sigma path error. There are 3 sites committed with 2 telescopes showing the locations of 2 sites and the third being west of Arizona where the telescope symbol is out of view.

In Arizona, especially in summer, there can be a preponderance of wildfires. It is important to get as much information as possible before travel. The image below shows a case where a number of fires are burning sending smoke plumes (at the time of the satellite image) in a certain direction.

Smoke from 6 different areas add to the cloud cover concern during the daylight hours. It is important to know wind direction and extent of smoke plumes before committing to a long drive.

THE MONSOON

This can be the most challenging time to pick a site (if mobile) or to remain at a fixed site. Clouds can be extensive and rain, hail, high winds are present. Forecast tools are not precise during that period from June 15-September 30. One must also know the elevation and azimuth of a star if traveling long distance then. Thunderstorm clouds can explode in a short time or move long distances day and night. As an example I had to drive from Phoenix west across the California border June 25, 2022 to escape a forecast of clouds over all of Arizona. On that day dry air was over California and being near the border at Blythe was the apparent best solution. But one thunderstorm cloud formed up near the border but remaining in Arizona. Yet I was likely 30 miles to the west having to plan to look literally into the cloud at occultation time some 3 hours in the future. I watched the cloud develop over 1.5 hours during which time the temperature at my location was 108 deg F. I moved 3 times before sunset just to try to anticipate future motion. Still it was not enough and 1.4 hours before the occultation I had to drive very fast further west.

Developing thunderstorm east of Blythe CA grew higher than 30 degrees and produced frequent lightning.

With time running out and uncertainty if my last minute drive would perhaps put me outside the occultation path I found the first road off I-10 and took it. It was a road to a California state prison west of Mesa Verde. I could see the peak of the cloud was below the altitude threshhold by about 8-10 degrees and looked stable. I was able to pick a desert spot 1 mile away so the lighting from the prison did not impact the view. However, little did I know that prison guard shift change occurred during the 30 minutes surrounding the occultation. Cars kept moving up and down the prison access road. But the light shield on my C8 held in place and the wind died down after sunset so that I was able to get a successful recording in spite of all the drama. I was inside the path in spite of driving 70mph madly down I-10 and not knowing for sure where I was.

Choosing a site is relatively simple using the Google map system where the + and – keys in lower right permit scaling up or down the view of a particular area. There are many dark roads in Arizona; however, if choosing to set up in side a town, use this map product to zoom in and check views from a candidate site for things like street lights and house density, abandoned buildings, fences, and high traffic roads. Use the predicted elevation and azimuth of the target star at the time of occultation to view that area of the sky for any such obstructions.

Overhead view of open terrain near the central line of the Burgundia occultation (green line). The terrain appears to be relatively flat. There are literally thousands of places within Arizona that feature good observing locations.

A horizontal view looking at the site area from highway 85. The terrain is indeed flat and unobstructed with few obstacles about which to be concerned. The small telescope symbol shows where it might be a good place to observe. This can be adjusted in real time. The video recording of the occultation will include a GPS set of coordinates: latitude, longitude and altitude regardless of where in the desert the site is located.

Finding an abandoned building could be a good idea for a number of reasons: 1) to serve as a wind break, 2) to find an easily locatable landmark to serve as an observation site, 3) to consider for reuse for future occultations. As an example consider the following images.

Google map image of what appears to be an abandoned building off a state highway

The above image shows a structure in an occultation path area that has a dirt road leading to it. Closer examination (next image) shows it really is abandoned and has easy access to a paved road as well as the interstate (I-17).

Closeup view of structure

After inspection the building turns out to be a perfect location and nobody else showed up during the occultation.

OBSTACLES THAT MIGHT ENCOUNTERED

Because there are so few major highways in the state it is always possible that an accident could shut a road down. This happens frequently and depending on the situation it can be shut down for many hours causing an abort for the occultation or a replan for a different route assuming there is time. Construction work in the Phoenix area occurs every weekend.

Car fire on the on-ramp to SR-51. Luckily it was possible to slowly get around it since the fire department had already put out the fire.

Then there is the occasional weather phenomenon that may or may not impact the decision to proceed to a planned site. Dust storms are not uncommon in the summer as a result of downdrafts from thunderstorms.

A dust devil estimated at well over 30m high spins east of mile marker 170 on I-10 during summer. Not serious enough to cause an abort but interesting to watch.

Unexpected highway signs may be encountered on Arizona highways.

Alert signs on I-17

Animals can present a danger at night to observers driving to the destination or to equipment left unattended. Javelinas and coyotes can be problems. One also need to be wary of ant dens, snakes, scorpions, bobcats, tarantulas, gila monsters (less so), elk and deer.

A large javelina (what other kind is there?) runs across a road in Carefree AZ.

This image of a rattlesnake I took beside my driveway before taking off for an occultation. These animals have good camouflage and it is advisable to scout all sites in daylight and conduct repeated flash light scans of your immediate area at night prior to/during observation.

A large cumulonimbus cloud forming prior to the start of monsoon. There was no lightning or rain but the clouds exploded quickly and moved toward a distant site. After 2 hours I could see the edge of the cloud mass had traveled more than 70 miles from Wickenburg to Flagstaff, AZ; but within 30 minutes of the occultation the cloud had evaporated and it turned out to be no threat at occultation time.

When choosing a site north of Phoenix accessible by I-17 one has to be aware of elevation/temperature differences which can have a large bearing on observer comfort and challenges.

The terrain in Arizona is such that an observer must plan for proper shoes, clothes and sun protection since various types of climates can be encountered. Even in summer when traveling to the high country a coat or gloves could be required. Thunderstorms can result in rapidly developing cells and hail forming as well as flash flooding. One should use multiple weather forecasting sites in order to anticipate day and night conditions during which travel is planned.

This can be a typical desert observation site.

Choosing a site can be quite challenging. The desert offers many really good possibilities yet one has to be extraordinarily cautious. In the image above the vehicle is parked too close to cholla cactus and in many cases it is advisable to have a 4WD in order to assure you will not get stuck in sand, ruts or other unexpected terrain. Observers should survey any site in daylight to assure safe entrance and exit at night, to avoid private property, avoid dry brush where parking a vehicle over it will not cause a fire to start, to retain all trash and never leave any of it in the desert and to walk the immediate area to look for animal footprints, ant dens, barbed wire, cliffs or other hazards, horizon obstructions, etc. It is always possible that the site chosen may have to be abandoned for unexpected reasons like the presence of people off-roading at night, someone shooting a gun in the area, the site being on tribal land and being ordered to leave by tribal police.

Danger from flooding in Arizona

Rain in Arizona is relatively infrequent but it is normal for rain to run off at high speed and flooding on flat roads that normally are in good condition is always possible. Storms can bubble up quickly especially in summer causing otherwise good roads to be blocked for hours as in the image above. Traveling for astronomical events should consider this important factor especially in areas of limited road availability.

Flat normally completely passable road on the way to a typical occultation observing site can look like this in just minutes. Imagine encountering this at night.

DRIVING PRECAUTIONS

Driving on Arizona highways offer a number of hazards. There are portions of 4 line highways that become two lane and in rural areas there is no roadway lighting. Passing on two lane roads can be dangerous and head-on collisions occur especially at night. When a car breaks down the shoulder of the road/highway is in many instances not wide enough for a vehicle to fully be off the road. A driver can get out of the car and be struck at night by oncoming cars. Also drivers are known to fix a tire literally at the edge of the roadway and be struck in that process. Highway patrol vehicles / state troopers have been hit by drivers at night that are not paying close attention and traveling at high speed. Animals darting across the road can cause accidents though it seems most desert animals (except for jackrabbits) stay away from major roadways. Trucks will normally move from the right lane to the left lane to avoid a vehicle stopped on the shoulder and occultation observers should do the same.

Headlights can be an issue. In the desert it is possible to mistake someone driving with normal headlights as someone driving with their bright lights on. New headlight designs can make driving even more distracting. New off-road lights and bars can be especially difficult to contend with when they appear heading in your direction. If already at a site at night off-roaders can sometimes be seen traveling at high speed creating dust clouds that can settle on telescope surfaces. One has to be ready to cover optics under such a situation.

DIFFERENT TYPES OF SITES IN WHICH TO CONTEND

In Arizona, some roads may not be safe to go off the road. Looking at particular locations in daylight is advisable. In other cases, it may be nearly impossible to find a site that is away from a highway as in the image below.

The site above was chosen south of Flagstaff because there was no other accessible place that provided the proper low horizon in the proper direction in order to see the star that would be occulted (15 degrees elevation above azimuth 115 degrees). This was an off-ramp to the top of a bridge crossing I-17. The telescope, after polar alignment, was pointed toward the target star but car lights from the highway did interfere somewhat with the background. Even so the observation was entirely successful although frustrating in the sense that a number of vehicles came up the ramp in the period prior to the occultation taking place. Not only is it recommended to choose a site off road and not visible from the closest road but to carry a cell phone in case of emergency. The map below shows 4G cell service coverage by Verizon but it should be warned that many places away from cities and towns suffer from places where no internet or cell phone signal can be obtained. US93 and I-17 are two highways where you can encounter such gaps. Open desert also experiences lack of cell towers/service.

Map showing Verizon cell service availability (pink) and no cell service (white) areas within Arizona.

At this site the wind was predicted to be higher than 10mph so I used a car to attempt to block it. A smaller low profile telescope was also used to insure the wind was unlikely to cause vibration during the data recording process.

Site location is important from a safety consideration. The above image is an abandoned Titan missile silo near Picacho, AZ. I had to be extraordinarily careful at night not to set up too close to the edge of the excavated hole.

Crossing the border into California will reveal desert terrain. One must be cautious about setting up near/at sand dunes if wind is expected. These are the Imperial Sand Dunes.

At other locations a wind block in the appropriate direction may only be behind a storage shed as in this shopping center (abandoned at night) near Gold Canyon, AZ

This location shows that in certain desert areas you cannot find areas that are brush free except near mower line easements. This one was near Black Canyon City, AZ

High winds caused me to set up my telescope between dumpsters as the only possible way to conduct an occultation. The site is in Tombstone, AZ

On yet another occasion it was so cold at the site that I was forced to rent a hotel room and take out the screen inside the room in order to point the telescope in the proper direction (elevation and azimuth). This successful occultation was also conducted from Tombstone, AZ

When the elevation of the star is low, but the star itself is bright and the wind is predicted to be high it may be possible to observe from inside an enclosed vehicle. In this case I was successful from a site near Dateland, AZ.

In yet another case I found a desert site that appeared to be perfect. However, I had to contend with the carcass of a dead cow for 2 hours prior to the (successful) occultation near Picacho, AZ.

Hardware set up on the desert floor near the carcass consists of a manually calibrated Celestron 8, knee pad, elevated stool and crate in which a laptop, IOTA VTI and Watec910HX camera are contained. If near a carcass you may need a mask to protect from the stench.

When an occultation occurs at a very low elevation (less than 10 degrees) it may not be advisable to go for it. But if that does happen pre-qualifying a site is mandatory to be sure there is no horizon blockage in the preferred direction. In the above case a tripod mounted 60mm refractor is used in 2015 and because it is summer and shorts are needed, a towel on the ground is mandatory during set up and observation.

There is always the unexpected. In this observation site at the Gila Bend, AZ airport a police cruiser pulls over a driver prior to the (successful) occultation. My telescope had to be located about 30m from the highway. Luckily both vehicles left before the critical time.

Sometimes it is not possible to quickly find a pristine site at just the right location. I had to settle for this junk yard in Ajo, AZ or have no site at all.

If one is superstitious it may be discomforting to find that the best observation site may be located in a cemetery. This one near Florence AZ was perfect for another successful adventure.

Where a site may be located close to a populated area it may be worth the effort to take a short time exposure image to see if the site qualifies. If not, reconsider another location.

A photo is used to determine if this site in front of a driveway is suitable for an observation site. The results look good.

Other unexpected challenges can exist. In this case my site near Payson, AZ was delayed by a huge holiday traffic jam; fortunately I started several hours early and was able to conduct the operation successfully.

One major challenge can occur when an occultation occurs during a Full Moon. With proper preparation a building or light shield can block moonlight but the problem that may be unsurmountable is when the distance between the target star and Full Moon is within 30 degrees or even less. The background may be so significant that even a high elevation site with good seeing conditions may not be enough to insure success. The above location is in Flagstaff, AZ.

One way to help counteract a Full Moon is to assemble cardboard boxes to block the Moon when the star is ‘close’ to it. This leaning tower of cardboard has worked well on several occasions from my site in Carefree, AZ.

Then there is the case where the site is perfect, the few clouds vanish, there are no obstructions and success occurs without incident. This site is near Picacho Peak, AZ.

In the summer it is not unusual to record data at night when the temperature is over 100 deg F as in this image above.

Challenges involved in recording such data include issues with receiving GPS signals, noise due to low signal to noise ratio, over integrating the target star image, under integrating the target star image, background interference from car lights, the Moon or twilight, etc. In the image above the laptop screen is free of bugs but when it is turned on, especially in summer, insects will flock to the screen.

The ultimate end result to hope for is shown above in the Pyote software graphic where a sharp drop and recovery are evidence of a solid occultation.