Before leaving the Lion, it is worth mentioning Wolf
359, which lies at R.A. 15h 54m.1, dec. 07 degrees 20
minutes. Apart from Barnard’s Star and the members of
the ·Centauri group, Wolf 359 is the closest of our stellar
neighbours, at a mere 7.6 light-years; even so, its apparent
magnitude is only 13.5, so that it is by no means easy
to identify. It is one of the feeblest red dwarfs yet to be
discovered, and its luminosity is less than^1 /60,000that of
our own Sun.
Cancer, the celestial Crab, which according to legend met
an untimely fate when Hercules trod upon it, looks a little
like a dim and ghostly version of Orion. It is easy to
locate, since it lies almost directly between the Twins
(Castor and Pollux, ·and ‚Geminorum) and Regulus; it
is of course in the Zodiac, and wholly north of the equator.
̇(Tegmine) is, in fact, a triple system; the main pair is
easy to resolve, and the brighter component is itself a
close binary, with a separation which never exceeds 1.2
seconds of arc.
The semi-regular variable X Cancri, near ‰, is worth
finding because of its striking red colour. As it never fades
below magnitude 7.5, it is always within binocular range,
and its colour makes it stand out at once. R Cancri, near ‚,
is a normal Mira variable which can rise to almost magni-
tude 6 at maximum.
The most interesting objects in Cancer are the open
clusters, M44 (Praesepe) and M67. Praesepe is easily
visible without optical aid, and has been known since
very early times; Hipparchus, in the second century BC,
referred to it as ‘a little cloud’. It was also familiar to the
Chinese, though it is not easy to decide why they gave it
the unprepossessing nickname of ‘the Exhalation of Piled-
up Corpses’. Because it is also known as the Manger, the
two stars flanking it, ‰and ÁCancri, are called the Asses.
Yet another nickname for Praesepe is the Beehive.
Praesepe is about 525 light-years away. It contains no
detectable nebulosity, so that star formation there has
presumably ceased, and since many of the leading stars
are of fairly late spectral type, it may be assumed that
the cluster is fairly old. Because Praesepe covers a wide
area – the apparent diameter is well over one degree – it
is probably best seen with binoculars or else with a very
low-power eyepiece. The real diameter is of the order of
10 to 15 light-years, though, as with all open clusters,
there is no sharp boundary.
M67 is on the fringe of naked-eye visibility, and is
easily found; it lies within two degrees of ·(Acubens).
It contains at least 200 stars; the French astronomer
Camille Flammarion likened it to ‘a sheaf of corn’. Its
main characteristic is its great age.
Most open clusters lose their identity before very
long, cosmically speaking, because they are disrupted by
passing field stars, but M67 lies at around 1500 light-years
away from the main plane of the Galaxy, so that it moves
in a comparatively sparsely populated region and there is
little danger of this happening. Consequently, M67 has
retained much of its original structure. It may be con-
siderably older than the Sun. Despite its great distance, it
is easy to resolve into stars, and in appearance it is not
greatly inferior to Praesepe. The distance from the Earth
is around 2700 light-years, and the real diameter is about
11 light-years.
Sextans(originally Sextans Uraniae, Urania’s Sextant) is
one of the groups formed by Hevelius, but for no obvious
reason, since it contains no star brighter than magnitude
4.5 and no objects of immediate interest to the telescope-
user, though there are several galaxies with integrated
magnitudes of between 9 and 12.STAR MAP 5
BRIGHTEST STARS
No. Star R.A. Dec. Mag. Spectrum Proper name
hm s ° ‘ “
32 · 10 08 22 11 58 02 1.35 B7 Regulus
41 Á 10 19 58 19 50 30 1.99 K0G7 Algieba
94 ‚ 11 49 04 14 34 19 2.14 A3 Denebola
68 ‰ 11 14 06 20 31 26 2.56 A4 Zosma
17 Â 09 45 51 23 46 27 2.98 G0 Asad Australis
70 ı 11 14 14 15 25 46 3.34 A2 Chort
36 ̇ 10 16 41 23 25 02 3.44 F0 Adhafera
Also above mag. 4.3: Ë(3.52), Ô(Subra) (3.52), Ú(3.85), Ì(3.88), È(3.94), Û(4.05) and Ó (4.30).
VARIABLE
Star R.A. Dec. Range Type Period Spectrum
hm °’ (mags) (d)
R0 9 47.6 11 25 4.4–11.3 Mira 312 M
DOUBLES
Star R.A. Dec. P.A. Sep. Mags
hm °’ ° “
· 10 08.4 11 58 307 176.9 1.4, 7.7
Ù 11 27.9 02 51 176 91.1 4.9, 8.0
Á 10 20.0 19 51
AB 124 4.3 2.2, 3.5 Binary, 619y
AC 291 259.9 9.2
AD 302 333.0 9.6
Áis a fine binary with an orange primary; it is out of binocular range, but a small telescope will split it.
The more distant companions are optical.
CLUSTERS AND NEBULAE
M NGC R.A. Dec. Mag. Dimensions Type
hm °’ ’
65 3623 11 18.9 13 05 9.3 10.0 3.3 Sb galaxy
66 3627 11 20.2 12 59 9.0 8.7 4.4 Sb galaxy
95 3351 10 44.0 11 42 9.7 7.4 5.1 SBb galaxy
96 3368 10 46.8 11 49 9.2 7.1 5.1 Sb galaxy
105 3379 10 47.8 12 35 9.3 4.5 4.0 E1 galaxyA dim Zodiacal constellation. The brightest star is ‚(Altarf); R.A. 08h 16m 30s.9, dec. 09° 11’ 08”, magnitude 3.52.
The other stars making up the dim ‘pseudo-Orion’ pattern are ‰(Asellus Australis) (3.84), Á(Asellus Borealis) (4.66),
·(Acubens) (4.25), È(4.02) and ̄(5.14).
VARIABLES
Star R.A. Dec. Range Type Period Spectrum
hm °’ (mags) (d)
R0 8 16.6 11 44 6.1–11.8 Mira 362 M
X0 8 55.4 17 14 5.6–7.5 Semi-reg. 195 N
DOUBLE
Star R.A. Dec. P.A. Sep. Mags Binary, 1150 y.
hm °’ °“ A is a close
̇ (Tegmine) 08 12.2 17 39 088 5.7 5.0, 6.2 binary, and there
is a 9.7-mag. third
component, P.A.
108°, sep. 288”.
CLUSTERS
M NGC R.A. Dec. Mag. Dimensions Type
hm °’ ’
44 2632 08 40.1 19 59 3.1 95 Open cluster
(Praesepe)
67 2682 08 50.4 11 49 6.9 30 Open clusterThe brightest star is ·: R.A. 10h 07m 56s.2, dec. 00° 22’ 18”, mag. 4.49. There is nothing here of interest to
the user of a small telescope.LEOCANCERSEXTANS R Leonis. The bright star
is ÔLeonis, at magnitude
3.8. The comparisons for
R Leonis are 18 Leonis,
magnitude 5.8, and
19 Leonis, magnitude 6.4.R1918ÔGa Atl of Univ Phil'03stp 2/4/03 7:36 pm Page 227