It has been 25 years since a grazing eclipse (also called ‘occultation’) of a reasonably bright star last crossed right through the middle of Houston. A grazing occultation is an eclipse of a star by surface features at either the north or south pole of the moon as moon moves through the night sky around the earth. In 1973 a graze of a Pleiades star was seen and timed by many observers from the Rice University campus. The next big event of this nature occurs on SATURDAY NIGHT, May 10, 2008 at 10:06pm, as a 6.3 magnitude star will graze the darkened north polar edge of the 38% waxing moon. The moon will be located 44 degrees elevation above the western horizon at that time. The occultation path runs northwest to southeast from Tomball, through Houston, Pasadena, Seabrook, San Leon, and Galveston Island (Bolivar side). The best places to watch the star disappear and reappear are between -0.1 and 2.0 km south of the centerline of the track. The name of the star that will be the focus of our efforts is Epsilon Cancri, the 5th brightest star in the constellation of Cancer. We hope to field a large observer team for this very important event and for once, even a small telescope can be employed to observe a series of interesting lunar phenomenon.
The purpose of this project and timing the star as it disappears and reappears from behind invisible mountains is to determine the absolute heights of lunar mountains and the depth of valleys between them. It is a fun and scientifically valuable adventure. NASA’s vision for space exploration includes a national goal to return to the moon to explore and establish outposts. It is more important now than ever to begin to accumulate current, accurate information to define the Moon’s topography.
The Epsilon Cancri event passes through Amarillo, Bryan College Station, and within driving distance of both Dallas and Lubbock. Maps for these areas are shown following the Houston discussion.
HOUSTON PLANS
We would like to have two persons at each observation site. So, if you have a friend or family member who
would be willing to help you, this would allow you to observe and not be preoccupied with monitoring
watching for cars, deer or other distractions. One person will use a small 3-inch (75mm) or larger aperture
telescope to call out as the star disappears (call out ‘out’) and then returns (‘back’). The second person
will handle the source of time signals which are needed to accurately link the timings of each event to specific
lunar features. [There is no point in having two telescopes with observers at the same location as this wastes
valuable resources]. The observer will need to use a standard microcassette tape recorder to record your
voice and time signals or if you have a sensitive video camera that can record 6th magnitude stars through
a telescope, that is event better. The star may disappear and reappear once or several times. Each observer
will see something completely unique from every other. The additive combination of all timings from sites
placed 50 feet apart (TBD) will enable us to create an indirect map of lunar mountains and valleys in
two-dimensional space with considerable accuracy. You will be watching for a six minute window starting at
10:03 pm and ending at 10:09 pm although the real action will happen over about a two minute portion inside
that period.
The tape recorder must record continuously and not be voice activated. In addition you will need a shortwave
time signal receiver. These can be found at places like Radio Shack and we recommend one that is digitally
tuned; for those who do not have them we intend to rebroadcast time signals on an FM frequency. So, please
bring either a high quality FM portable radio with fresh batteries or consider using your FM car radio.
The frequency to receive time signals will be provided about a month before the occultation on this web
page. Because we are using a low power FM transmitter, you will likely have to crank up the volume fairly
high in order to receive the signals. You will have to be careful to position your tape recorder, radio and telescope
close to each other so that the volume from your voice and radio can EVENLY record on the tape.
Figure 1. The path as it goes over the Houston area. The observation zone lies ONLY between the parallel
black lines. South and west of the lines a total occultation can be seen. North and east of the lines no
occultation occurs. Most of the track goes through heavily traveled or lighted areas which is why we
picked the key road in the following figures. It is much less traveled and has good views along the entire
path.
HOUSTON AREA SITE
I have scouted a number of places around Houston. The least intrusive area and one where cars can be parked
at the site easily is located in Seabrook along Old Hwy 146.
Figure 2. The Seabrook area, located about 25 miles southeast of downtown Houston. The best route is to take
hwy 225 east to hwy 146 south. Use Mapquest or another tool to help you find your way to the location and
back.
Figure 3. An intermediate view of the road where observers will be located. This is Old Hwy 146 between the
two arrows. If you are coming south on 146, take the Red Bluff Exit which is located after the Port Road
exit. Turn left and go a very short distance to Old Hwy 146. You will see cars along the road, so ask for
your assigned site.
Figure 4. Close up of the site area and where you should go for your site assignment.
Figure 5. The above map shows how the moon will look to the naked eye at the time of occultation.
The dark side of the moon is shown shaded and the arrow points to the position of the star just before
things start to happen. There are elevation and azimuth markers that are depicted along the axes of
this graphic. You will be facing due West and the moon located half way up from the horizon to the
overhead point.
PRACTICE ON THE MOON DURING SIMILAR PHASES:
The moon will be at a similar phase around March 12 and again April 10. Use these dates to take a look at the
moon through your telescope to get an idea what eyepiece you would need to keep about 1/4 of the moon in the field
of view. If your scope is not clock driven, you will have to push it to follow the star as it approaches the
dark side of the north pole. Note where the north and south pole are as seen in your telescope. They will likely
appear inverted.
WATCH THIS VIDEO
If you have never seen a grazing occultation before, and perhaps just a bit nervous about trying to time something
completely new, then don't worry! You can get a first hand look by going on line to watch a great video of
a real occultation of a star grazing the moon as seen from near Hockley, TX this summer. This file is rather large
(about 300MB). Click on:
Video.
This link requires a media player like RealPlayer to view. You can see in real time as the star is covered and
uncovered repeatedly as the moon passes between us and the star. The field of view is similar to what you
can see in an eyepiece, though you want to keep as much of the bright limb out of the field as you can.
Some of the events (an ‘event’ is either a disappearance or reappearance) are rather quick, some take
many seconds. Some may be instantaneous; some may take a fraction of a second to occur. A ‘blink’ or
‘flash’ is also possible as the star appears to clip the top of a mountain. Hence, it is important to
watch and not to talk (except for calling ‘out’ and ‘back’) during the observing window until the
occultation is over.
It is also possible to appreciate how important it is to focus the telescope properly. This video was
easily recorded on the very sensitive and relatively inexpensive Supercircuits PC164 video camera
(available from http://www.supercircuits.com located near Austin) which operates from DC power; the
video output of the camera feeds into a camcorder which acts as the VCR. A lot of camcorders may
not accept video input so be sure your camcorder has that feature. Video is much more accurate than
the human eye and of course, the disc or tape can be analyzed, replayed and preserved. Time signals
must be recorded in order for the data to be of use. So, if you do not have a digital short wave radio
(e.g. from Radio Shack capable of receiving WWV on 2.5, 5.0 and 10.0 MHz), don’t worry as we will rebroadcast
those signals for you on FM for a short period of time beginning prior to and ending shortly after the
graze.
If you think you might want to come out for this and help us record data or would be willing to help out
with logistics such as site marking, tape pickup, etc., we really need your assistance. We are looking
mainly for observers, but also those willing to help check telescopes for new observers to be sure they
are looking at the correct star and troubleshoot equipment problems. Please contact me at
pdmaley@yahoo.com or at 281.2440208 during the day.
YOUR HANDS
If you are by yourself and have a telescope without a motor drive, your hands will be very preoccupied. You must
find a way to push the scope to follow the star, keep the star in focus at all times, hold the tape recorder
close to your mouth, and call out the disappearances and reappearances that you see. Please practice before
hand by simply gathering your equipment in one place--even during the day inside your house--and pretending
that you are tracking the moon. You can also do it outside in the daytime when the moon is visible or even
at night when the moon is also up. This practice will give you a better appreciation for any possible
difficulties. One sure way to fail at this is not to practice and arrive at the observation site totally
unprepared!
MAY 10 DETAILED TIMELINE FOR HOUSTON AREA OBSERVERS: PRINT THIS OUT ONLY ON MAY 10 (NOT BEFORE) AND TAKE IT WITH YOU!
9:00am or later - gather all your equipment. Be sure you have fresh batteries, the tape(s) are rewound and
that everything is in working order. An example checklist should include: eyepieces; telescope, mount, chords and power
sources, tape recorder(s), radio(s), this web page with the timeline, light shield, chair to sit on, small table to
put equipment on (if needed), extra batteries, map to the site, anything else vital such as snacks, tapes, discs,
something to write with.
6:00pm - A GO or NO GO will be DECLARED at this time. I will record a message.
Call 281.4809878 at 6pm or later. If the phone message says THE OCCULTATION IS CANCELLED, do not drive down.
8:45-9:00pm - Arrive at the site area NO LATER THAN THIS TIME. Base your arrival on the amount of time it takes to set up
your telescope and equipment afterward. When you arrive, stop at the intersection noted on the map in figure 4. You
will receive your stake number. Proceed to the stake, set up your telescope as close to the stake as you can.
9:30-9:40pm - Time signals will be broadcast for a 10 minute test period on FM 88.9MHZ (backup on 89.1).
IMPORTANT TEST! Have your telescope pointed at the moon, radio and tape recorder positioned where you need them to be.
Turn on the radio and tune in the best time signal frequency of either 2.5, 5.0 or 10MHZ. If you are using an
FM radio, tune to that frequency. Now, pretend to look through the telescope,
turn on the radio and recorder and record your voice along with the time signals for 15 seconds or so. Stop the
recorder, play it back and see if the time signal volume and your voice recorded evenly. If one drowns out the other,
you will need to reconfigure until you can clearly hear your voice and the signals at the same level.
9:40pm - be sure you are pointed at the north pole of the moon and are looking at the correct star. If you are
not sure you are looking at the right place, ask for help from a nearby station. Use figure 5
above to locate the star relative to the cusp. The figure is set up as you would view the moon in binoculars or
with the naked eye. In most telescopes, the appearance of the star and moon limb
will be REVERSED from the way it appears in figure 5. So, be sure you are looking at the right pole of the moon.
Since you are facing west, push the telescope to the right (that is, in the direction of north). If the moon drifts
out of the field of view as you move it in this direction, then you are probably on the correct pole. Should your
telescope not have a clock drive, you will have to manually track the star to be sure it does not get away
from you in the minutes prior to the start of observation.
9:50pm - time signals will start again for real for 20 minutes on FM radio 88.9MHZ (backup 89.1).
10:02pm - turn on your radio and let it play time signals continuously.
10:03:30pm - turn on recorder and begin non stop observing of the star. Call 'out' or 'back' each time when the star
disappears and then returns. Be as quick as you can and note any delays. BE SURE THE STAR IS ALWAYS IN PROPER FOCUS.
10:08:30:00pm - stop observing. Turn off all equipment.
10:15pm - Be sure you have recorded your name, designated site number, names of others present, phone,
telescope information, eyepiece used, method of recording (video, photoelectric, visual, etc.), whether
a clock driven mount was used or if you had to manually track, information on any problems you might have
encountered (cloud, mosquitoes, etc.). TURN IN THE TAPE BEFORE YOU LEAVE. If you have recorded on video tape, you
can reduce the tape yourself or leave it with us. Note, all tapes will NOT be returned. If you prefer, you can take
the audio tape with you,copy it and then mail it in to me.
OTHER TEXAS CITIES
Observers in Amarillo, Bryan, Lubbock, Dallas areas should click
Map Limits and use the interactive
map to zoom in on your area. Then, enter the values of
-0.1 in the top open box and 2.0 in the second open box, clicking on each box to draw two separate lines. Those
lines define the zone where you should set up sites. Use the zoom feature to find your city and locate
good observing sites within the zone. Let me know what you plan to do. Use the timeline above for your
own planning except subsitute the start/stop observation times as noted below.
It is important to note that the times for the occultation will be different for each location. The times for
your observations are listed below.
Figure 6. The path as it goes through Amarillo TX.
Observe beginning 9:46pm, end at 9:52pm.
Figure 7. The path passes about 70 miles northeast of Lubbock TX.
Observe beginning 9:51pm, end at 9:57pm.
Figure 8. The path is about 80 miles southwest of the center of Dallas and passes just near Stephenville.
Observe beginning 9:56pm, end 10:02pm.
Figure 9. The path as it goes just east of downtown Bryan TX.
Observe beginning 10:00pm, end at 10:06pm.
Observers from the above cities are requested to participate and to contact me when/if ready to observe.
