Sky & Telescope - January 2023 - 45

Evenings with the Stars by Fred Schaaf
The Hare and the Dove
Two small constellations are nearly overshadowed by
their brilliant neighbor.
O
n clear January evenings it's impossible
to ignore the brilliant constellation
Orion. But don't overlook two
surprisingly bright and interesting characters
just below the heavenly Hunter:
Lepus, the Hare, and Columba, the Dove.
The Hare's brightest stars are only
a little dimmer than Delta (δ) Orionis,
the easternmost Belt star and the
faintest of Orion's seven main lights.
Six additional stars in Lepus exceed
magnitude 4.0, making the figure an
easy sight under moderately dark skies.
The Hare's brightest light is 2.6-magnitude
Alpha (α) Leporis. It's also known
as Arneb, which appropriately enough
is the Arabic name for " hare. " Arneb
occupies the center of Lepus, about 18°
due south of Orion's Belt and more than
one hour of right ascension due west of
Sirius, the night sky's brightest star.
Arneb is a most distinctive star. It's
about 2,200 light-years from Earth and
has an absolute magnitude of -6.6. What
is absolute magnitude? Astronomers
use two different figures to describe a
star's brightness. The more familiar is
apparent magnitude - how bright a star
appears in the night sky. That's useful,
but what if we want to know how luminous
a star actually is? That's where
absolute magnitude comes in.
It's calculated using a star's apparent
magnitude and its distance. Absolute
magnitude tells us how
brightly a star would shine if
it were placed at a standard
distance of 32.6 light-years.
That might seem oddly
arbitrary, but it's based on
another unit of distance: the
parsec. The parsec is determined
by observing how
a star's position in the sky
changes as measured from
opposite sides of Earth's
orbit, six months apart. If
the star shifts 1 arcsecond,
it would be at a distance of
1 parsec, which is equal to
3.26 light-years. So, the standard
distance of 32.6 lightyears
is simply 10 parsecs.
If Arneb were at distance
of 32.6 light-years, it would
AT THE FEET OF ORION Two
of the winter sky's lesser-known
constellations lie south of mighty
Orion, the Hunter. Lepus, the
Hare, and Columba, the Dove,
may not shine as brightly as their
northerly neighbor, but each has
its own attractions.
easily outshine the planet Venus at its
brightest. However, our own Sun at that
same distance would glow relatively
dimly at magnitude 4.8 - fainter than
most of the stars making up Lepus.
Beta (β) Leporis, also known as
Nihal (from an Arabic word for a certain
kind of camel), shines at magnitude
2.8 and lies a modest 160 lightyears
from Earth. That's a lot closer
than Arneb but quite a bit farther away
than Zeta (ζ), Eta (η), and Gamma (γ)
Leporis, which are 70, 49, and 29 lightyears
away, respectively. Gamma is well
known to telescope users as a beautiful,
easy double star with 3.6- and 6.3-magnitude
components of yellow and red,
separated by a generous 96″.
Just south of Lepus is Columba, the
Dove. I initially thought that both were
among the smallest of the 88 officially
recognized constellations. Not so. In
fact, 34 constellations occupy less celestial
real estate than Columba, which
itself is a bit smaller than Lepus.
Lepus is often pictured as being
chased by Orion's hound dog, Canis
Major, but hares and rabbits have many
astronomical connections. One is the
" Moon rabbit, " in which the lunar feature
Mare Crisium serves as the hare's
round tail or " scut. "
Columba is most often connected
with the biblical tale of Noah and the
ark. Noah released the dove to seek
dry land during the Flood. And indeed,
Columba is not far from the huge constellation
of the ship Argo, which was
broken up into Vela, Puppis, and Carina.
Columba features the creditably
bright Alpha Columbae, a 2.7-magnitude
star known as Phact (Arabic for
" ring dove " ). But my favorite Columba
attraction lies near its border with
Canis Major. That's the location on the
celestial sphere that our solar system is
flying away from in its journey around
the galaxy. A formal name for that
point is the Antapex of the Sun's Way or
the solar antapex. But a name for it I like
even more is " the Sun's Quit. "
¢ FRED SCHAAF first identified Orion
when he was six years old, Lepus no
more than two years later.
sk yand tele scope .o r g * JANUARY 2023 45
ALEXANDER JAMIESON / CELESTIAL ATLAS (1822) / UNITED STATES NAVAL
OBSERVATORY LIBRARY / PUBLIC DOMAIN
Sky & Telescope - January 2023

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