OF THE ROGER N. CLARK

--
Brightest stars of the Pleiades
VISUAL ASTRONOMY OF THE DEEP SKY
Star Name Magnitude Star Name Magnitude
25 Tauri Alcyone 2.87 19 Tauri Taygeta 4.29
(Eta) 28 Pleione 5.09
27 Atlas 3.62 16 Celaeno
5.44
17 Electra 3.70 21 Asterope 5.64
20 Maia 3.86 18 5.65
23
Merope 4.17 22 6.41
observation proved different, however, because
the nebula could be seen well at as high
as 82 X. And when the magnification was
increased tD 117 X, the nebula became easier!
Under excellent conditions, the Merope
Nebula is easily seen in the 3-inch finder at
31X.
The Pleiades' many and varied stars and
delicate nebulosity provide a beautiful view
to the amateur. It is no wonder the cluster is
called the most studied and photographed of
astronomical objects.
6.2 ·
7.7 ·
Pleiades
6.8 .
7.0 ·
Pleione
• Alcyone
Atlas . (2.9)
(5.1) •
(3.6)
.6.2
6.6 ·
6.S-
7.3-
7.0 ·
Asterope
•
(5.3) •
7.4 ·
Maia.
(3.9)
• Merope
(4.2)
• Taygeta
Figure 7.1. The brightest Pleiades, with
visual magnitudes. To the naked
Asterope appears single; the magnitude is
combined light of both stars.
6.2-magnitude star at upper left is also
naked-eye blend. From Sky &
November, 1985.
(4.3)
M l (NGC 1952), THE CRAB NEBULA:
SUPERNOVA REMNANT IN TAURUS
RA. 05h 34.5m, Dec. 220 01' (2000.0)
Technical. Messier I has been known as the
A VISUAL ATLAS OF DEEP-SKY OBJECTS
Crab Nebula ever since the third Earl of Rosobserved
it with his 36-inch telescope in
44. In _the drawing he made, the nebula's
filaments suggest the legs of a crab. Photoments
throughout a diffuse green oval.
and certainly the youngest Messier object. It
is the expanding remnant of a brilliant
naked-eye supernova that was seen in July,
1054. Now 5 by 3 arc-minutes in size, Ml is
raphs show a beautiful network of red fila­
M1 is one of the youngest objects in the sky
growing by nearly a half arc-minute per century.
Changes have been photographed in
only a couple of decades.
Ml is about 6000 light-years distant and 6
light-years across. It is one of the strongest
radio sources in the sky and also emits strong
X-rays. Near the center of the nebula is a
16th-magnitude star that flashes 30 times a
second in visible light, radio, and X-rays.
This is a pulsar, the superdense neutron-star
core of an old supernova. It is thought to be
only 20 kilometers in diameter, and so dense
that a teaspoonful of its matter would have a
mass of several million tons! The flash rate
corresponds to its period of rotation. Its very
strong magnetic field spins with the star 30
times a second; energetic electrons trapped in
the field produce the radiation. The pulsar is
actually pumping energy into the nebula, so
the expansion rate is increasing.
Visual. M I can be seen in binoculars and
small telescopes as a small, faint patch. With
a visual magnitude of 9 and a size of about 5
by 3 arc-minutes, it has a mean surface
brightness of20.6 magnitudes per square arcsecond.
Large amateur telescopes under dark
skies will show some of the filaments, though
they are often difficult.
At low powers (60X or less) few details are
visible. At higher powers the nebula's outline
begins to depart from a smooth oval. In the
8-inch at 188X, the "bay" to the east is visible,
and the whole thing takes on the appearance
of two oblong nebulae side by side. No
stars could be seen inside the nebula with the
8-inch, but many were around it.
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95