Sky & Telescope - May 2023 - 50

MAY 2023 OBSERVING
Celestial Calendar
Action at Jupiter
May 2005
October 2005
One of my favorite stories about Chi
Cygni concerns its discovery. Johann
Bayer recorded the star in his 1603
Uranometria atlas, but the first person
to recognize its variability was German
astronomer Gottfried Kirch, in 1686.
While observing the nova known today
as CK Vulpeculae (in the neighboring
constellation, Vulpecula), Kirch noticed
that Bayer's Chi Cygni was missing. Several
months later it returned, establishing
the star's variable nature.
Most long-period variables are of
spectral type M, but Chi belongs to the
rarer spectral type S, whose stars are
richer in carbon as well as zirconium.
Convection currents dredge these
elements from the star's interior and
deposit them in the outer layers.
Spectrographs show lots of dark
absorption bands in Chi's light caused
by zirconium oxide and other molecules
March 2006
May 2006
pThis sequence of infrared images, made
in 2005 and 2006 with the Infrared-Optical
Telescope Array optical interferometer, reveals
the changing shape and brightness of the
pulsating red giant star Chi (χ) Cygni, located
approximately 520 light-years from Earth. Images
show up to a 40% variation in the star's
diameter as well as hot spots and changes in
the amount of limb darkening.
in its cool, distended atmosphere. Like
all Mira-type stars, Chi's outer layers
expand and contract as it seeks (and
fails) to reach equilibrium.
The star's cyclic palpitations affect
both its luminosity and size. Over its
408-day cycle, Chi's diameter varies
from approximately 195 million kilometers
(121 million miles) at maximum
brightness to as large as 464 million
kilometers at minimum. That's 140
to 333 times the diameter of the Sun!
Picture that when you lay eyes on Chi
Cygni this month.
Occultation Rehearsal
THREE MORNINGS BEFORE it occults
Jupiter, the Moon will take a swing at
Psi3 (ψ3) Aquarii, a 5th-magnitude star
that forms part of a compact trio in
eastern Aquarius that also includes Psi1
and Psi2 Aquarii.
On May 14th, observers across the
eastern two-thirds of the U.S. will
witness some part of the occultation.
From the East Coast,
the bright limb of the
waning lunar crescent
covers the star
in morning twilight,
but the reappearance
occurs close to
or after sunrise and
won't be visible.
Midwesterners
will miss the ingress
but catch sight of
50 MAY 2023 * SKY & TELESCOPE
the star popping back into view on the
Moon's dark limb in morning twilight.
Psi3 should be plainly visible in even
the smallest telescopes and probably in
tripod-mounted binoculars, too. Farther
west in the Mountain states, the star
reappears shortly after moonrise in
complete darkness, but at low altitude.
(The occultation won't be visible from
the West Coast.)
For precise times
for your location, run
a simulation on your
astronomical software
of choice, as described
previously.
This simulated view
shows the 5th-magnitude
star Psi3 Aquarii moments
before it's covered by the
advancing lunar crescent.
AFTER A ONE-MONTH absence,
Jupiter emerges at dawn from its
April 11th conjunction with the
Sun. As a new apparition begins, the
planet will initially be a somewhat
disappointing telescopic sight, owing
to its low altitude for much of the
month. From mid-northern latitudes,
on May 6th (roughly the first
morning it'll be visible to the naked
eye) Jupiter sits just 1.4° above the
east-northeastern horizon 30 minutes
before sunrise. By the 15th, that
figure has improved to 5.2°, and on
the 31st to 13.3°. The planet reaches
opposition in autumn, on November
3rd. For telescope users, the most
rewarding span of this apparition is
bracketed between August 22, 2023,
and January 30, 2024. The first of
those dates corresponds to when the
planet reaches the meridian by the
start of morning civil twilight (when
the center of the Sun is 6° below the
horizon). The second date is when
Jupiter first crosses the meridian
as evening civil twilight begins. Of
course, that's simply a rule of thumb
- the planet can be enjoyed well
beyond those two dates.
Any telescope reveals the four big
Galilean moons, and binoculars usually
show at least two or three. The
moons orbit Jupiter at different rates,
changing positions along an almost
straight line from our point of view
on Earth. Use the diagram on the
facing page to identify them by their
relative positions on any given date
and time. All the observable interactions
between Jupiter and its satellites
and their shadows are tabulated
on the facing page. Find events timed
for when Jupiter is at its highest.
Features on Jupiter appear closer
to the central meridian than to the
limb for 50 minutes before and after
transiting. Here are the times, in
Universal Time, when the Great Red
Spot should cross Jupiter's central
meridian. The dates, also in UT, are
in bold. (Eastern Daylight Time is UT
minus 4 hours.)
INTERFEROMETRIC IMAGES: SYLVESTRE LACOUR, OBSERVATOIRE DE PARIS;
OCCULTATION SIMULATION: STELLARIUM
Sky & Telescope - May 2023

Table of Contents for the Digital Edition of Sky & Telescope - May 2023
