The Caldwell Objects

this state of affairs.) The Hyades may well have
more in common with the 400-million-year-old
Praesepe star cluster, M44 in Cancer, which also
shares their motion through space.
Naked-eye stargazers and binocular users
will find several attractive pairs of stars within
the Hyades. Most obvious are the Theta Tauri
and Delta Tauri groupings in the middle of each
branch of the V. Theta 1 and Theta 2 (θ 1,2 ) Tauri lie
halfway between Aldebaran and Gamma Tauri
inside a squashed ellipse of 5 th-and 6thmagnitude
stars. Theta 1 and Theta 2 Tauri shine at
magnitude 3.8 and 3.4, respectively, and are 5.6'
apart on a roughly north-south line. Ptolemy may
have seen these stars as one, but today they are
not considered a particularly exacting test of
visual acuity. Type-Ay Theta 2 Tauri is the
brightest true member of the Hyades and is about
50 times more luminous than our Sun. Fainter
Theta 1 Tauri is 9 light-years farther away It is a
type-G7 yellow giant, so be sure to compare it
with that non-Hyad, Aldebaran. Through his 6inch
refractor Adm. William Henry Smyth
described the colors of the Theta 1,2 pairing as
pearly white and yellow. The Delta Tauri stars
(δ 12 Tauri) are a much more open pair (18') in the
western branch of the V. Here we have a
magnitude-3.8, type-G8 yellow giant and a hot
A7 main-sequence star shining at magnitude 4.8.
Since naked-eye doubles abound in the
Hyades, visual athletes can try for the following
bronze-, silver-, and gold-medal pairs. You
deserve a bronze medal if you can split Sigma 1,2
(σ 1,2 ) Tauri, about 1° southeast of Aldebaran. The
stars shine at magnitude 5.1 and 4.7,
respectively, and are separated by 7.2' along a
south-southwest to north-northeast line. That's
more than twice the angular distance between
the components of the famous naked-eye double
star Epsilon 1,2 (ε 1,2 ) Lyrae (magni-
The Caldwell Objects
41
tudes 5.0 and 4.7, respectively). Christian
Luginbuhl and Brian Skiff found it "relatively
difficult" to split the Sigma Tauri stars, but I
found the task relatively easy. In binoculars the
Sigmas shine with a comparable pearly white
luster. Astronomers once believed that Sigma 1
Tauri did not belong to the Hyades, but the
Hipparcos satellite revealed that both components
are true cluster members. The silver medal
goes to anyone who can split Kappa 1,2 (κ 1,2 ) Tauri
in the Bull's ear. These two type-A7 stars
(magnitude 4.2 and 5.3, respectively) are a bit
tighter than the Sigmas, being separated by only
5.6'. The appreciable magnitude difference
between the two components makes the task all
the more difficult. In the 1923 edition of
Astronomy with an Opera-Glass, Serviss thought it
"improbable" that anyone could separate the
Kappas with the naked eye. Of course, I wouldn't
have included the Kappas if I didn't separate the
stars myself and believe you could do the same.
Try looking at the Sigmas and the Kappas
between nautical and astronomical twilight
(when the center of the Sun's disk is between 12°
and 18° below the horizon, respectively). During
this time of subdued illumination the contrast
between the stars and the background sky is
reduced, enhancing the eye's ability to resolve
close pairs.
You get the gold medal if you can resolve 80
and 81 Tauri. These magnitude-5.6 and 5.5 stars
are separated by about 8'; their faintness makes
them more challenging than the Sigmas or the
Kappas. (By the way, 81 Tauri is a telescopic
double with a 9th-magnitude companion 2.7' to
the northwest.) Of course, I couldn't stop there,
so I added another prize category. The Superman
or Wonder Woman Medal goes to anyone who
can separate the unnumbered pair of stars just
30' northeast of Theta 1,2 Tauri. These stars shine
at magnitude 4.8 and 6.5, respectively, and are
separated by a mere 4' —
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