Rare Easy Naked-Eye Asteroid Eclipse in southern Europe Oct. 19
On Wednesday Morning, October 19th, observers in a 35-km-wide path can watch the bright star Regulus wink out for just a second
This is rarer than an annular or total solar eclipse; the next similarly bright eclipse by an asteroid at least this large will not occur until March 2014, that one in the northeastern U.S.A.
Best view is in southern Spain and Portugal. There's some dawn twilight, but view good in southern Italy, too. Strong twilight will make it harder to see in Greece, but binoculars will give a good view there.
Updated: 2005 October 17, 17h UTOn Wednesday morning, October 19th, the asteroid (166) Rhodope will eclipse the star Regulus, the brightest star in the constellation Leo (the Lion) for only a second in a path crossing southern Portugal, southern Spain, southern Italy, and Greece. If you live in or near the predicted path, astronomers want YOUR help to observe the eclipse to help trace the asteroid's outline and search for possible satellites of Rhodope. In Spain, the occultation will occur at 6:23 am local time, just before 6:24 am. In Portugal, the time is only a few seconds earlier, but the time zone is different, so the local time there will be 5:23 am. In Italy and Greece, it will occur at 6:24 am, Middle European Daylight Time.
Last Update Here of Plans
The weather forecasts now are favoring southern Italy and Portugal, and also probably clearing in southwestern Spain. I plan to catch my flight from Baltimore to Madrid, arriving in Madrid around 10 am tomorrow (Tuesday Oct. 18). If the forecast is not much different from what it is now, I will get my rental car and drive to southern Portugal. In Madrid, I will keep in touch with Arturo Montesinos, cell phone (+34) 670204741, with backup Jose Ripero (+34) 639101618. In Portugal, I will try to keep in touch with Rui Goncalves, phone (00351) 96.2703985 - for some, (00351) should be (+351). Rui pointed out that the time zone is different in Portugal from Spain, so the event will occur in Portugal at 5:23 am local time, still 4:23 UT, as in Spain; I've corrected this above.
The Path of the Eclipse
Maps and other information about the path of the eclipse can be found on Steve Preston's Web site. It shows a view of the world as seen from the asteroid with the line representing the path crossing it. From that page, you can link to more detailed maps and information, for example, a map showing the path across southern Europe and the Middle East (in most of Turkey, northern Syria, northern Iraq, and northern Iran, the eclipse takes place in daylight, after sunrise, but could be seen there with small telescopes). But at least from southern Italy westward, it will be easy to see for those with moderately good eyesight with naked eyes. The country maps on Steve Preston's Web site (the one for Spain also includes southern Portugal) show the expected locations of the northern and southern edges of the path in red. But the path location is uncertain by more than a path-width; the red lines enclose a broader area within which the eclipse has a 68% chance, at least, of taking place (somewhere within that zone, in a 37-km-wide path). This is called the "1-sigma uncertainty zone". An interactive google-maps-based map, allowing you to zoom in with great detail with satellite views that, at their best resolution, show roads, fields, and many buildings, but no identifying names or numbers, is here, prepared by Charlie Ridgway. It shows the predicted central line in yellow, the northern and southern edges of the predicted path in purple, and the edges of the 1-sigma uncertainty zone are pink. Geoff Hitchcock, or "Kiwi Geoff", has a similar map here that includes the capability to plot gray lines offset from any specified distance from the central line, useful for helping mobile observers to select sites that might avoid lines that will be covered by fixed-site (such as observatory) observers. Kiwi Geoff's map uses Steve Preston's latest (October 12) path update that uses new observations made earlier this month at Table Mountain and Ondrejov Observatories; this new prediction is 14.5 km, or almost half a path-width, south of the previous predictions. Carles Schnabel near Barcelona has prepared some detailed maps of the path across Spain and Portugal using Jan Manek's new (Oct. 12) prediction, which is 12 km north of S. Preston's; you can see these maps here. Jan Manek uses 2-sigma data for the error bounds of the path, meaning that there is about a 95% chance for the actual path to be somewhere within the error bounds. Arturo Montesinos has prepared some detailed maps showing towns and road intersections along the A4 and A30 highways in Spain. I have put all of Carles Schnabel's maps (he updated them with Manek's latest prediction), and Montesinos' maps, in this Word file.
List of Cities and Stations
Jan Manek gives lists of cities and stations ordered by distance in km from the central line on his Web site. These can be used to help coordinate coverage of the event, seeing where fixed-site observers are located so that mobile observers can avoid duplicating their observations. The time of closest approach for the station, and the altitudes of the star and of the Sun, are also given. Unfortunately, none of the stations or cities are within the predicted path, so more detail is needed. A list of stations, currently using Steve Preston's predicted path, is on Derek Breit's Web site. He uses a newer version of Occult than the one Jan Manek uses; Breit's list includes the probability of seeing an occultation for each station not included in Manek's lists. As you can see from Breit's list, the probability of seeing the occultation is almost the same at the center (43%) as at the limits (37%). If the event is going to be observed at all, mobile observers need to spread out to try to cover at least the 1- sigma uncertainty zone as well as the predicted path rather than all bunch up at the center, where there is a 57% chance that NO occultation will occur. Later this weekend, Derek Breit, and probably also Jan Manek, will add Montesinos' stations along the A4 and A30 highways in Spain, and we will try to add some additional towns and observatories in and near the path. If you have any suggestions for locations to add, preferably with latitudes and longitudes please send them to me, and/or to Derek Breit at breit_ideas@hotmail.com and Jan Manek at jan.manek@worldonline.cz and we'll add them to the list.
Weather
The long-range weather forecast is still poor for Iberia and for southern Italy, according to a forecast Web site provided by Jose Ripero. The forecast for Madrid can be found here. At that site, other cities can be added, and hourly details can be seen for two days in advance. For later days, a breakdown by day and night is given. The forecast there currently for both Tuesday night, Oct. 18 and Wed. day, Oct. 19, is for rain showers for all cities across southern Iberia, and also for Messina, Italy. Hopefully, the forecast will improve closer to the time of the event.
Finding Regulus is easy
The star, Regulus, is the brightest star in the constellation Leo, a "first-magnitude" star, one of the 25 brightest stars in the sky, so it can be seen even in light-polluted cities. Regulus will be seen rising in the east; the nearly full Moon, in the western sky in almost the opposite direction, will not interfere. If you look in the opposite direction from the Moon, the brightest object you will see will be orange-colored Saturn, about halfway from the horizon to overhead in the east. Regulus is the bright star almost directly below Saturn.
These full-sky charts, produced with the heavens-above.com Web site, can be used to help locate the star. They show the horizon as a circle with north at the top, south at the bottom, east to the left and west to the right. Overhead is at the center of the circle. To translate to the real sky, you can hold the chart over your head with the side with the Moon pointing towards the Moon in the west; that will orient the map with the sky.
There are four charts, the first two being for Iberia and the last two computed for Italy, but also good enough for Greece. On all of the charts, Regulus is underlined, and the Moon and planets (Mars and Saturn) are named. The first chart for each group includes standard connecting lines to form the constellation forms, the constellation names, and the names of the the stars that, except for Polaris, are as bright as, or brighter than, Regulus. The second chart removes the connecting lines and names (except for the names of Mars, Saturn, and Mo on), showing what the sky will really look like (except, of course, the sky is dark with bright stars, not black stars on a white background).
Observing the Eclipse
You can watch the occultation with the naked eye, but for some, especially in Greece where twilight will be bright, it will be better to observe the eclipse with binoculars or opera glasses steadily held against a post, fence, top of an automobile, or other sturdy object, or mounted on a tripod. An eclipse of a star, gamma Ceti, which is almost 10 times fainter than Regulus, by the asteroid (6) Hebe was observed without any optical aid in Mexico City on 1977 March 5, and on 2003 June 24th, I saw an eclipse of a similarly bright star, Zavijava, by the asteroid (124) Alkeste in Australia.
Location
Select an observing location that you can return to and describe within an accuracy of 30 meters, such as "10 meters south of the center of east-west Road A and 40 meters west of the center of intersecting Avenue B in Mytown, Andalusia" or "in my back yard, 15 meters from the center of my house at 473 Road X in Ourcity, Italy". Streams and buildings (specify the address) can also be used as references. If you are mobile, select a location a safe distance from traffic and away from houses, especially ones with barking dogs.
Timing the Eclipse
Just knowing whether or not an eclipse of Regulus occurs is useful, especially if your location happens to be near the actual edge of the eclipse path, or if a small moon of Rhodope briefly eclipses the star at your, or a nearby, location. But timing the eclipse, especially its duration, will add much value to your observation. Those with camcorders can make the most accurate timings - see below. At a minimum, just count as fast as you can from the time the star disappears, and remember the number you reach when it reappears. Then, find a friend with a stopwatch, or digital watch with stopwatch function, and time how long it takes you to count to the reappearance number. Of course, it would be better if you can time the eclipse yourself with a watch. If you have (or can borrow) two watches (or if the one you have can time two intervals), start both watches when the star disappears, stop one when it reappears, and stop the other one at a specific word in one of the radio broadcasts specified below. Try to remember any delay in starting or stopping the watches at the disappearance.
Recording the Eclipse
Even better is making an audio recording of the eclipse using either a tape recorder or a camcorder (using the audio part). Use the tape recorder to record one of the radio broadcasts below, and also your shouts when the eclipse starts and ends (use "D!" for the disappearance and "R!" for the reappearance). Many tape recorders now are voice-activated, which can spoil a timing sequence; turn off that feature if you can. If not, keep talking or play the radio loud enough for its dialog to keep the tape recorder going. Make a test recording beforehand, and play it back to be sure you can hear both the radio broadcast and your comments. In some cases, especially near the edge of the path, more than one eclipse can occur quickly as two parts of an irregularly-shaped asteroid covers the star. Also tell when you start watching the star and when you end your observation of it, and any interruptions in watching the star due to passing clouds or any other reason.
Best of all is recording the star and the radio broadcast with a camcorder. Many camcorders are sensitive enough that they can record a star as bright as Regulus. First, use the camcorder's autofocus to focus on some distant lights, then switch to manual focus. Image the Moon and finetune the focus. Zoom in so that one or two fainter stars can be seen and use the star charts (see above) to locate Regulus. Be sure you have enough tape to record for the minute of the event (it is only necessary to record from the start of 6:23 am to the end of 6:25 am, for all observers across southern Europe, if you know the time accurately). If you use a "night shot" setting, the frame rate will be lower and you will loose some time resolution, but that will probably be better than just a visual observation. If your camcorder can record the star in normal mode, use that. If you have a telescope, you can find the star with it, then point the camcorder into the eyepiece to record it, but this "afocal" method can be difficult (test it first). An electronic eyepiece or video camera inserted into the eyepiece holder, with the output recorded with a camcorder or VCR, will be easier.
Radio Stations for Timing the Eclipse
The national broadcasts on certain strong standard AM medium-wave radio stations, receivable with most automobile and home radios, can be used for timing the eclipse; the ones we want you to use are listed below. If you have a short-wave radio, it would be even better to use the time signals broadcast by stations in Russia at 5.0 and 10.0 megaHz. A wire antenna about 10 meters long can help improve reception. Recordings of the eclipse should record the broadcast during the critical minutes, but if this is not possible because the radio is inside and can not be moved, then start the recording five minutes before, recording a few minutes of the broadcast, then (keeping the camcorder or tape recorder recording) go outside to record the event, and if an eclipse occurs, then go back inside to record a few more minutes of the broadcast before stopping the recording.
Tests need to be made to see if telephone time is accurate enough. In most countries, it is not accurate enough for these observations.
The AM stations that we plan to use for timing have not yet been selected, and unfortunately so far nobody has suggested any to use, or offered to make an accurately-timed recording of any. Volunteers are needed to record a strong AM station in their region along with an accurate time base such as DCF77 or GPS time. If you could do this, it could help many others obtain accurate timings.
Reporting Observations
If you observed Regulus during the 6:23 to 6:25 am time interval, please send a report giving the times you started and stopped observing the star (include the times of any interruptions) and your location (see that section above) to the coordinator for your country listed below, whether or not an eclipse occurred at your location. If you know the longitude and latitude of your location, preferably with a GPS measurement or measured from a detailed topographic map, give that, but if not, just give a careful description of the place. If an eclipse did occur, include the duration, or disappearance and reappearance timings, in the report and any comments about them, including how you made the timings. If you obtained an audio or video recording of the eclipse, include that fact in the report so that you can be sent an address to which the tape, or a copy of it, should be sent for analysis. You can just send a simple message with the information above, or you can obtain a plain ASCII text form, editing it with Notepad or most any other word processor, or, with Netscape, you can fill out a Web form interactively here.
Links and Contacts for Local and Regional Coordinators
Carles Schnabel is the coordinator for Spain, with e-mail address oculta@astrosabadell.org. He has distributed a message about the occultation to almost 100 Spanish observers; you can see his message here in Spanish or in English. Carles Schnabel and other observers from Sabadell plan to observe the event from locations near one of the north-south highways in the Alicante region. Jose Ripero near Madrid, e-mail jripero@vigiacosmos.com , plans to observe the occultation from the central line in Almuradiel, south of Valdepenas. Costantino Sigismondi, e-mail c_sigismondi@yahoo.com , is planning to observe from southern Italy and is trying to coordinate some observations with students from the University of Calabria. In Portugal, Rui Goncalves, e-mail rui.goncalves@ipt.pt , plans to observe the occultation from the Grandola service station on the A2 highway about 6 km south of the central line; he notes that many Portuguese amateur astronomers know about the event, but most of them live outside the predicted path.
Information about Rhodope and Regulus
Rhodope was the 166th asteroid discovered, on 1876 August 15 by Christian Heinrich Friedrich Peters in Clinton, New York. Rhodope is named after a queen of ancient Thrace, the wife of Haemus. Haemus was vain and haughty, comparing himself and Rhodope to the Greek gods Zeus and Hera, who were offended and changed the couple into mountains that straddle the current border of Greece and Bulgaria. Rhodope orbits the Sun with an average distance 2.68 times that of the Earth in the main belt of asteroids between Mars and Jupiter. Comparison of infrared and visual wavelength measurements indicate that Rhodope's diameter is about 35 km. Measurement of Rhodope's light variations show that it rotates with a period of 7.87 hours. Rhodope is a GC:-spectral class asteroid, meaning that its reflectance colors are "carbonaceous", dark like coal. Rhodope is a member of the Adeona family of asteroids, meaning that it has orbit parameters similar to the 155-km asteroid (145) Adeona, so it was likely formed from a collision of another asteroid with Adeona millions of years ago. Some more information about Rhodope is here but that Web site gives a larger diameter of the asteroid, 60 km, based on older observations. Of course, a main goal of observations of the October 19th eclipse will be to find out Rhodope's actual size. On October 19th, Rhodope will be 460 million kilometers, or 3.073 times the average Earth-Sun distance, from the Earth.
The name Regulus is "little king" in Latin; it marks the location of the heart of Leo, 77 light-years or about 730 trillion km (or 1.6 million times the distance of Rhodope) from the Earth. It is a blue-white star, about 50 million years old (very young as far as stars go; our Sun is 5 billion years old). Regulus has a rotation period of only 16 hours, much faster than the Sun's 28-day rotation period; this is so fast that astronomers estimate that if Regulus were to spin only 10% faster, it would fly apart. More general information about Regulus can be found here. Regulus's dimensions were recently measured to be 4.2 times the diameter of the Sun in its equator but only 3 times the Sun's diameter in its polar direction, directly showing the large flattening caused by its fast rotation. I like the picture at the top of this Web site showing an observer pointing an old telescope at Regulus; hopefully on the morning of October 19th, many others will be looking at Regulus to see the eclipse by Rhodope. Some images showing an eclipse (called occultation) of Regulus by the Moon is here.
History of Asteroid Eclipses
Asteroids are small and far away, making it very difficult to predict their eclipses of stars (called "asteroidal occultations" by astronomers). The first one, by the large asteroid (3) Juno, was observed in Sweden in 1958. It was not until the mid-1970's that the paths of the larger asteroids were determined accurately enough to predict some of their occultations. Some of these early observations indicated that some asteroids had small moons, but that inference remained controversial until the Galileo spacecraft imaged Dactyl, the satellite of the asteroid (143) Ida, on its way to Jupiter in 1993; now, about 30 asteroids are known to have satellites.
Over 700 asteroidal eclipses have been observed, most of them during the last seven years after accurate directions for over 2 million stars were measured from space, without the distortions of the Earth's atmosphere, by the European Space Agency's Hipparcos satellite. The sizes and shapes of dozens of asteroids have been measured from timings of their eclipses of stars made mainly by amateur astronomers. Most of these involve stars requiring medium- sized telescopes to observe. Eclipses of stars as bright as Regulus by asteroids as large as Rhodope, where the path can be predicted rather well and the star can be seen without optical aid, occur only once every two or three years, usually over oceans or lands with few if any potential observers. Click here for results from past events. If the weather cooperates, with your help the October 19th Rhodope eclipse could become the best-observed asteroidal eclipse.
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I am planning to travel to Spain to observe the Rhodope eclipse myself, arriving in Madrid on October 18th at 9:40 am. I hope to coordinate and work with Spanish observers, to find out the latest weather forecasts, best places to observe, etc.
David Dunham, President, International Occultation Timing Association (IOTA) e-mail: home, dunham@starpower.net office david.dunham@jhuapl.edu telephone: home, +1-301-474-4722, office +1-240-228-5609 cell phone +1-562-430-2391 (sorry, not international)
