On Wednesday night, Oct. 23 at 11:08pm PDT (Oct. 24 at 6:08 UT), there will be
an important occultation, of 10.2-mag. UCAC4 362-196994 in north-central
Capricornus by (16) Psyche, the heaviest known M-type asteroid , and is thought
to be the exposed iron core of a protoplanet , the remnant of a violent
collision with another object that stripped off its outer crust . Radar
observations of the asteroid from Earth indicate an ironânickel composition.
This unusual object is the target of NASAâs âPsycheâ space mission that
will launch in 2022 and arrive at Psyche in January 2026. For these reasons,
the brightness of the star, and the wide (and thus rather certain) path, this
occultation was selected as IOTAâs most valuable asteroidal occultation of
2019; see http://occultations.org/campaigns/ ;(listed after the Sept. Octavia
âmost observableâ occultation), although the later-added (3200) Phaethon
occultations were close rivals.
The occultation will be visible across southernmost California, with the
predicted northern limit crossing Orange County, Riverside, and n. of Needles,
but with the possible path errors, it could be over Long Beach or Riverside. In
Arizona, the event occurs around 11:09pm MST, with the path covering most of
the state, with the expected n. limit over Kingman and n. of Tuba City
(Flagstaff will have a nearly central event), and the s. limit over Maricopa
and s. of Queen Creek, so nearly all of the Phoenix region can expect an
occultation, with shorter events towards the southeast. In Phoenix, the
altitude will be 13 deg. in the southwest (azimuth 237 deg.), so your
observation site will need to have a view unobstructed by trees or buildings in
that direction. The altitude will be higher in California, but lower as you go
east. The southern limit passes over Albuquerque, where the altitude will be 10
deg., and the n. limit could pass over Colorado Springs, where the altitude
will be only 6 deg. (so observers there would need to be far enough east so
that the Rockies will not block the view). In the other direction, the
occultation will also be visible from the southern part of the island of
Hawaii, with the n. limit just north of Kilauea volcano, but possibly as far
north as Hilo and Mauna Loa; the time there will be just before 6:05 UT (8:05
pm HST of Oct. 23).
The Principal Investigator of NASAâs Psyche mission is Lindy Elkins-Tanton of
Arizona State University at Tempe, which along with the rest of the greater
Phoenix region, is within the wide predicted path of the occultation, with
nearly a 100% chance for an event.
Thereâs uncertainty in the starâs magnitude; 10.2 is from Gaia. But the GSC
says 12.4 and APASS gives the V-magnitude as 11.4 with B 13.0. The large B-V
indicates a red star, like the star occulted by Phaethon on Sept. 29 where
there were similar differences; the star may be variable. Weâll check the
starâs visibility this Sunday evening, to see how observable it is with small
telescopes. In the case of the Sept. 29 th event, the star was not as faint as
APASS said, but fainter than the Gaia magnitude.
Psyche might have satellites that could pose a navigation hazard for NASAâs
mission, so observers throughout the western USA are encouraged to try this
event, at least from convenient home, or near-home, locations. A page about the
occultation is at http://occultationpages.com/rasc/20191024_16Psyche.html . ;
The target star is at J2000 RA 20h 52m 01.0s, Dec -17 deg. 44' 36". Steve
Prestonâs prediction for the event, with event details and finder charts of
different scales, is at
http://www.asteroidoccultation.com/2019_10/1024_16_62878.htm . The target star ;
is 7 deg. east-southeast of 3 rd -mag. beta Capricorni (Dabih), 3 deg. west and
a little south of 4 th -mag. theta Capricorni (Dorsum), and 38 arc min.
west-northwest of 5.2-mag. 19 Capricorni = SAO 163975 at J2000 RA 20h 54.8m,
Dec -17 deg. 55â. We hope that some observers outside the path will travel
into it, and that more who live within the expected path will sign up for this
valuable rank 100 occultation. Please let me or Occult Watcher know if you can
try this important occultation; we donât want to duplicate your chord with
one of the several remote stations that we plan to deploy.
There are some pre-point opportunities that will allow you to point your
telescope to the precise altitude and azimuth that the occultation star will be
during the occultation, including one with 8.5-mag. SAO 163929 (J2000 RA 20h
51.0m, Dec -17 deg. 46â) only 1m 1s (61s) before the occultation. The other
brighter earlier prepoint opportunities should be used by all, to check for
visibility of the target altitude and azimuth from the site you chose, early
enough so you can change the location, if necessary. Iâll describe these in a
future message.
David
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