Royal Astronomical Society of Canada

International Occultation Timing Association

Notes for planetary/asteroidal occultations given in the 2019 RASC Observer’s Handbook. The text in bold font following the date, and for some events, the object name, is given here but is not in the Handbook.
Jan. 3: (433) Eros was mapped by the NEAR spacecraft in 2000-2001. The star = TYC 0823-00693-1, spectral type F5.
Jan. 4: This is of special interest since (90) Antiope is binary with nearly equal components. The star = TYC 3336-00404-1, spectral type K5.
Jan. 21: Venus’ 21² disk will be 58% sunlit. Only the dark-side reappearance can be seen, but it can be observed well since the sunlit parts of Venus will be about 9² away. Those with large telescopes may see the star faintly 1 or 2 minutes before the predicted reappearance, due to refraction of the star’s light in the atmosphere. A boat or airplane will be needed to see the central flash since the central line of the occultation passes only over the Pacific Ocean southwest of Baja California. SAO 160163 = TYC 6226-01500-1, spectral type A0.
Feb. 18: The star is ZC 1815 = SAO 138892, spectral type K2III, angular diameter 0.002². For a central occultation, the disappearance and reappearance of the star will take 0.8s and there will be zones 8 km wide at the northern and southern limits where the star will be only partially occulted. The star has two large planets. 9^th-mag. stars are 3¢ and 5¢  away.
Feb. 19, Jurgenstock: Sirius, the brightest star in the night sky, is a Canis Majoris = HIP 32349 = SAO 151881, spectral type A0mA1. Its angular diameter is 0.006². The asteroid’s angular diameter will be 0.005², smaller than Sirius, so even an observer on the central line will see the star fade down and back up in about 1.5 seconds, the value given in the table for the maximum duration, including the effect of the star’s diameter, although there will be no complete occultation of the star. The remaining light of Sirius A is likely to render invisible the 8^th-mag. white dwarf companion, Sirius B. The current 1-s cross-track error is at least 6 times the path width, so unless the orbit of the asteroid can be improved, such as with GAIA data, before the event, several stations will need to be set up across the path to ensure that even one of them has an event. The asteroid is named after Jürgen Stock, a Venezuelan astrometrist who died in 2004.
Mar. 10: The star is TYC 6823-01469-1, spectral type F1V. A 10.8-mag. star is 23² away in position angle (PA) 264°.
Mar. 19, Apollonia: The star is HIP 19036 = SAO 93749, spectral type K2III.
Apr. 11: The star is TYC 4949-00427-1 = UCAC4 450-53228, spectral type F8. A 10.8-mag. companion is 15² away in PA 303° that won’t be occulted.
Apr. 23: Carme is the 11^th satellite of Jupiter, an irregular object of special interest to Brazilian astronomers.
June 16: The star has a companion, TYC 6852-00453-1, of similar brightness 12² away in PA 197°.
July 23: The star is HD 275682. It has a 12^th-mag. companion 23² away in PA 89° that is not occulted.
July 31: The star is HIP 6268, spectral type G0. It has a 13^th-mag. companion 3² to the north that will be occulted in the south Pacific Ocean and maybe in the coast of South America at dawn.
Aug. 28: Hektor, the largest Trojan asteroid, is about 400 km long and 200 km across in the other directions, a contact binary. It also has a 12-km moon, Skamandrios, in a 624-km orbit with period 3 days that will also occult the star somewhere.  The star is TYC 6931-00826-1.
Sep. 15: The star is a companion of 7th-mag. SAO 78231 which is 21² away in PA 65° and won’t be occulted.
Oct. 24: Psyche is the largest metallic (M-type) asteroid and is the target of the NASA Psyche mission. The Guide Star Cat. gives the magnitude of the star as 12.4, so it may be a red star.
Nov. 14, Althaea: The star is ZC 635 = HIP 20205 = Hyadum I, spectral type G8III, at the bottom of the Hyades “V”.
Nov. 23: The star is SAO 78596 = HIP 31850, spectral type F8IV.
Dec. 7: The star is HIP 24832, spectral type A7V. A 12^th-mag. star is 4² away in PA 173° and won’t be occulted.

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                                                                                                        2019

                                                                                         PLANETARY OCCULTATIONS
                                                     By David W. Dunham, David Herald, Steve Preston, and Derek Breit

     As major, dwarf, and minor planets, and their moons, move across the sky, they occasionally pass directly between an observer and a distant star, producing an occultation. Astronomers have learned much about solar system bodies by carefully monitoring the changing apparent brightness of stars during the immersion and emersion phases of occultations. If the occulting body does not have an atmosphere, the occultation is virtually instantaneous; if there is an atmosphere, it causes the star’s disappearance and reappearance to occur gradually. If a planet has rings or other debris in its environs, the extent and degree of transparency of this material can be precisely mapped. The rings of Uranus, the ring arcs of Neptune, and the atmosphere of Pluto were all discovered by occultation observations. If an occultation is observed at several distributed sites, the size and shape of the occulting body can be determined more accurately than by other Earth-based techniques.
Amateur astronomers can make important contributions to occultation observing campaigns. This is particularly true for minor planet occultations, for which the paths across Earth are often very narrow and uncertain in location (due mainly to uncertainties in the ephemeris of the minor planet). By recording the times of the star’s disappearance and reappearance as seen from several sites (i.e. by noting the edges of the minor planet’s shadow as it sweeps across Earth), the object’s profile can be directly determined. Often timings of adequate accuracy can be made by visual observers using modest telescopes.
When observing an occultation, it is important that an observer know his or her location to within a fraction of a kilometre. Geographic longitude and latitude as well as the altitude of an observing site can be determined with a GPS receiver, from a high-quality topographic map, or from some map websites. If observations are to be of maximum value, the times of immersion and emersion must be determined as accurately as possible-certainly to better than 0.5 seconds, and better than 0.2 seconds for the shortest events (those less than about 10 seconds in duration). Photoelectric equipment with high-speed digital recording systems is well suited for this work. Attaching a low-light-level video camera to a telescope is a less expensive method for accurate timing. Visual observers using tape recorders and shortwave time-signal receivers can also make useful contributions. Even simple measurements of the duration of an occultation made with an ordinary stopwatch can be of value. CCD observers should be aware that most of these systems are incapable of timing accuracies better than about 2 seconds; hence visual observation may be better. Some CCD observers use the trick of turning off the telescope clock drive shortly before the predicted time and let the images trail. The occultation will appear as a break in the trail that can be measured to about a tenth of a second if the moment the exposure is started (just after turning off the clock drive) is accurately timed.
Occultation observations are coordinated in North America by the International Occultation Timing Association (IOTA)  IOTA member or not, IOTA wants to inform you, and others in your area, able to locate stars to 11th magnitude of prediction updates. Please email the longitude and latitude (or location from the nearest town) of convenient observing sites, telescope size(s), and an indication of whether you are mobile to dunham"at"starpower.net. Individuals interested in joining IOTA should refer to OCCULTATIONS BY THE MOON, p. 1xx in this Handbook, for membership information.
More information is in the Solar System Photometry Handbook (Willmann-Bell, Inc., 1983), Sky & Telescope, and occasional papers in the Astronomical Journal, Icarus, Minor Planet Bulletin, and other scientific journals.
Observations of occultations by major and minor planets, including negative observations, should be sent to reports"at"asteroidoccultation.com for analysis and publication by IOTA. When reporting timings, describe your geographic longitude, latitude, and altitude (to the nearest arcsecond and 30 meters, respectively), telescope size, timing method, the start and end time of observation, an estimate of the observer’s reaction time (if applicable) and the accuracy of the timing, and whether the reaction time correction has been applied. The report forms at www.asteroidoccultation.com/observations/ are preferred; observational results are also posted there, as well as much more useful information.

Table of Planetary Occultations
     The following two-page table (see p. 2xx) of planetary occultations by major, dwarf, and minor planets visible from North America and Hawaii for 2019, is based on predictions by Edwin Goffin, Scott Donnell, Steve Preston, Derek Breit, and David Herald. Preston and Breit assisted Dunham in the selection for the two-page table. Most of the occultations are by asteroids, but there is one occultation by Venus and one by Carme, one of the small outer moons of Jupiter. Of special interest are occultations by distant trans-Neptunian and Centaur objects, many of which have moons and some rings. In general, special astrometric observations with large telescopes are needed to predict these occultations well enough for observing campaigns, and these are accomplished usually only a few weeks before the occultation. The few of these events that can be predicted several months in advance are too faint for most amateur telescopes and so are not in our list. These events are announced on Web sites of the Paris Observatory Lucky Star Project, the Rio astrometry group, and RECON, the network of observatories in the western USA dedicated to these observations. But most observers are informed of them via IOTA’s Occult Watcher software described below, via its Lucky Star and Rio group prediction “feeds”.
The successive columns in the table list: (1) the date and central time of the event; (2) the name of the occulting body; (3) the apparent magnitude of the major or minor planet; (4) the catalogue and number of the occulted star; (5) the star’s apparent visual magnitude; (6) the star’s right ascension and (7) declination; (8) the expected magnitude change from the combined brightness; (9) the predicted maximum duration of the occultation in seconds; and (10) the approximate region from which the occultation is predicted to be visible (locations are listed chronologically from first to last). Due to uncertainties mainly in the ephemerides of the minor planets from which these predictions are derived (most star positions are now accurately determined from the European Space Agency’s Gaia mission), the region of visibility of an occultation is uncertain, by about half a path-width for most of the asteroidal occultations listed. Errors may remain, so those near but outside the paths should try to observe. It’s also useful, especially for the brighter stars that produce high signal-to-noise recordings, to observe even if you are located up to about 10 path-widths from the predicted path, to check for the possibility of an occultation by a previously-unknown satellite of the asteroid. Updated maps and more about these events is at http://www.poyntsource.com/New/RASC_Events.htm.
Note that the times are usually for the geocentric time of closest approach; for any specific location in North America or Hawaii, the event time can be several minutes earlier or later.  A few weeks before each event, improved predictions and the latest path maps may be obtained from Steve Preston’s minor planet occultation website: www.asteroidoccultation.com. Much other useful information, including interactive maps to zoom in on the path, circumstances for dozens of stations in and near the path, and lists of stars that can be used to pre-point telescopes to the target stars are at http://www.poyntsource.com/New/Global.htm. “Occult Watcher” finds many other minor planet occultations visible from your site or region; it is a free download from http://www.hristopavlov.net/OccultWatcher/publish.htm. Since Occult Watcher works from an interactive Web site, IOTA uses it to coordinate minor planet occultation observation plans.
Star catalogs are abbreviated as follows: SAO, Smithsonian Astrophysical Observatory; ZC, Robertson Zodiacal Catalog; TYC, Tycho-2; PPM, Roeser Positions and Proper Motions; HIP, HIPPARCOS, and UCACx, xth .U. S. Naval Observatory CCD Astrographic Catalog.
Some event stars, marked by * in the main table, have alternative star numbers, shown in the table below:
Planet # is the minor planet number and the alternative star number (Alt. Star #) is from the HIPPARCOS-mission catalogs used for the predictions on IOTA’s minor planet occultation Web sites mentioned above. When known, spectral types (Sp.) are listed for the stars in the table.

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