Sky & Telescope - December 2023 - 49

Vesta Ambles
Across Orion
IF YOU LIKE TAKING a celestial ride
don't miss the Vesta train. The solar system's
brightest and second-largest asteroid
comes to opposition on December
21st, when it shines at magnitude 6.4.
While this year's isn't a particularly
bright or close apparition, the asteroid
will be easy to spot in binoculars and
the most modest of telescopes. Vesta
moves steadily westward in retrograde
motion across northernmost Orion
until the 28th, when it crosses into
neighboring Taurus. On opposition
night Vesta will be less than ½° northnortheast
of 4.4-magnitude Chi1 (χ1)
Orionis, one of the stars in the Hunter's
upraised club. As it drifts westward,
the asteroid passes north of 3rd-magnitude
Zeta (ζ) Tauri on the nights of
January 7th and 8th, and sits about ½°
south of the famed Crab Nebula, M1,
from January 11th to 13th.
Vesta's high northern declination
makes it a tempting target for testAn
Asteroid
Eclipses
Betelgeuse
A REMARKABLE OCCULTATION will
take place on December 11-12 when
the 14th-magnitude main-belt asteroid
319 Leona passes directly in front of
Betelgeuse (Alpha Orionis) and hides it
for several seconds.
At the time of writing there are
slight uncertainties in the ground path
and times, though astronomers will be
carefully observing additional Leona
occultations in the meantime to nail
down the details. For the latest update,
visit the International Occultation
Timing Association's (IOTA) page at
https://is.gd/leona2023.
Both Leona and Betelgeuse have
apparent diameters of around 50 mil6h
20m
Cr 89
NGC 2129
µ
GEMINI
NGC 2175
Dec 1,
2023
3 5 7 9 11
13 15 17 19 21 23
χ2
η
Jan 2,
2024
25 27 29 31
χ1
4 6
ζ
+20°
8
10 12
M1
+22°
6h 10m
M35
+24°
6h 00m
5h 50m
5h 40m
5h 30m
TAURUS
3
4
5
6
7
8
ξ
+14°
ing your visual acuity and your sky's
naked-eye limiting magnitude. Pick a
moonless night when the asteroid forms
a simple and easily recognizable pattern
liarcseconds, but due to the uncertainties
in Leona's size - which could be
anywhere from 50 to 81 kilometers (31
to 50 miles) in diameter - the brightness
drop could be as little as 0.5 magnitude
all the way up to near-extinction.
The most likely scenario is an annular-style
eclipse with Betelgeuse quickly
dimming, reaching a momentary minimum,
and then returning to its normal
brightness. Along the path's centerline,
the occultation could last nearly 12 seconds.
In locations where Leona partially
eclipses Betelgeuse, the event will be
shorter and have less dimming.
Southernmost Florida is the only
place in the U.S. where the occultation
is visible. The centerline passes over
Everglades National Park and just south
of Homestead, where the occultation
takes place around 8:25 p.m. EST on
December 11th with Betelgeuse some
24° above the eastern horizon. The
partial-eclipse zone extends north to
with nearby field stars, as it does on
the 23rd. Allow at least half an hour
for your eyes to dark-adapt, then use
averted vision to sight Vesta.
include Miami and south to the Florida
Keys. The event will also be visible
from parts of eastern Mexico, southern
Europe, Turkey, and central Asia.
Leona is a coal-black asteroid that
resides in the outer realm of the main
belt. Initial observations seemed to indicate
an 18-day rotation rate, but recent
data suggest a much shorter period
of just 18 hours. This discrepancy is
one reason we don't know the object's
true size. A further complication arises
because the size and shape of Betelgeuse
is variable, affected by massive convective
cells that burp blobs of the star's
atmosphere into space, changing its
apparent size and shape. Hubble Space
Telescope images reveal that the star is
decidedly non-spherical.
If it turns out Leona's apparent size
equals or exceeds that of Betelgeuse,
the occultation will be a dramatic sight
anyone in the occultation path with
clear skies can view with the naked eye.
sk yand tele scope .o r g * DECEMBER 2023 49
+18°
+16°
ORION
ν
Path of Vesta
Star magnitudes
https://www.is.gd/leona2023 https://skyandtelescope.org/
Sky & Telescope - December 2023

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