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R^ RUBINfor observers at mid-northern latitudes
as it transits the meridian. The most
convenient star-hops begin at Theta (θ)
and 29 Capricorni.
The Moon in the days immediately
following opposition will be more of a
nuisance — the full Moon on August
15th will certainly interfere — but as
the Moon wanes, Psyche remains well
placed for observation, culminating
earlier with each passing night. By the
end of the month, Psyche transits about
an hour before midnight and stands
only 2° lower than it did on the night of
opposition. Taking a second look at the
asteroid will help you verify your fi rst
observation, as Psyche will have traveled
to a new position.
Psyche’s a fascinating object. It’s
small, about 210 km (130 miles) across
on average, and metallic, composed
mostly of iron-nickel. Psyche’s pure
metal composition has led planetary
scientists to conclude that the asteroid
could be the remnant core of a planet
that’s been stripped of its outer lay-
ers through repeated collisions. If this
turns out to be the case, Psyche would
be the only metallic planet core discov-
ered to date and would offer a chance
to fi nd out more about our Earth’s and
other planetary cores, buried as they
are beneath the mantle and crust.
Arizona State University and NASA’s Jet
Propulsion Laboratory are planning a
mission to Psyche, scheduled to launch
in 2020 (https://psyche.asu.edu).
This will be the fi rst mission to study a
metal asteroid.
After you’ve sketched the location
of Psyche in your observing logbook,
move northeast to search for asteroid
15 Eunomia. Eunomia reaches opposi-
tion on August 12th, when it rises in
an evening sky already held by a waxing
gibbous Moon. This means that the
asteroid will be easier to observe earlier
or later in the month, weather permit-
ting. Shining at magnitude 8.2 at oppo-
sition, and 8.3 on the night of August
6–7 (Psyche’s opposition), Eunomia
is noticeably brighter than Psyche.
It’s also higher in the sky, crossing
the meridian about halfway between
horizon and zenith all month. Betaskyandtelescope.com • AUGUST 2019 49
(β) Aquarii is the closest bright star to
Eunomia’s path in early August.
Italian astronomer Annibale de Gas-
paris, observing from Naples, discovered
Eunomia in 1851. Composed of silicates
and nickel-iron, Eunomia holds about
1% of the asteroid belt’s total mass. Like
Psyche, Eunomia has a history full of
impacts and collisions, but some 75%
of its original material is thought to
remain intact. The other 25% belongs
to the Eunomian family, a group of
roughly 6,000 stony bodies that orbit in
the intermediate asteroid belt.
Asteroid 39 Laetitia offers a chance
for an observing trifecta: three mov-
ing targets in a single night. Laetitia
reaches opposition on the night of
August 16–17 — hello, Moon! — so
grabbing it earlier in the month is a
good idea. The 5th-magnitude star 46
Capricorni is a good starting point for
an early August star-hop.
Laetitia follows a path that runs
northeast to southwest across Aquarius
and Capricornus this summer. The
asteroid moves from Aquarius into
Capricornus the fi rst week of July, then
returns to Aquarius in early Septem-
ber. Laetitia is at its brightest for the
year, magnitude 9.1, near opposition.
However, it’s just a little dimmer,
magnitude 9.4, on the night of August
6–7, when it culminates at an altitudeof 41° or so. By the end of September,
Laetitia’s brightness drops to magni-
tude 10.1, out of binocular range unless
you break out the 15×70s.
Discovered in 1856 by the French
astronomer Jean Chacornac, Laetitia
is, like Eunomia, a stony main-belt
asteroid. The most recent measurements
obtained by Wide-fi eld Infrared Survey
Explorer (WISE)/Near-Earth Object
WISE suggest that Laetitia has an
irregular ellipsoidal shape with an aver-
age diameter of 180 km (112 miles). It’s
possible that Laetitia is a binary system,
with two similarly sized components
orbiting a common barycenter.pThis artist’s concept shows the 5-panel solar arrays of the spacecraft proposed for the Psyche
mission. The spacecraft will “cruise” for 3½ years on solar-electric power to reach the asteroid,
then spend 21 months in orbit around the metal world.Just getting started with aster-
oids? Check out the Asteroid
Observing Program sponsored
by the Astronomical League (AL).
The program is designed to help
AL members learn how to observe
and identify asteroids. A 4-inch
scope is recommended to get
started on your list. To observe
dimmer asteroids, the AL recom-
mends a 6-inch scope. You’ll also
need to be ready to sketch at the
eyepiece. Visit the program web-
site at https://is.gd/astrcobs for
more information.