My first Magazine Sky & Telescope - 04.2019 | Seite 28

Constellation History
β
–60°
–61°
Rigil Kentaurus Tr 22
V737
–62°
–63°
14 h 50 m
V737
Hadar
5617
–62°
Lynga 2
CENTAURUS
Proxima
Centauri
α
CIR
3
4
CENTAURUS
5
6
7
8
Proxima
Centauri
6
7
8
9
10
11
–63°
14 h 40 m
14 h 30 m
14 h 20 m
14 h 10 m
14 h 00 m
14 h 40 m
14 h 35 m
14 h 30 m
14 h 25 m
14 h 20 m
p NEEDLE IN A HAYSTACK A good chart is essential for identifying faint Proxima Centauri within the densely packed Milky Way star fi eld. There are
many cases of stars that appear to be members of a binary pair and are actually chance line-of-sight coincidences. Proxima is a rare example of a
star that is known to be gravitationally bound to another but appears to be completely unrelated. In all likelihood such cases are common, but they’re
hard to detect unless they’re extremely close by.
hole that’s consuming large quantities of gas and dust. As the
material spirals into the black hole, a fraction of it is ejected
in high-speed jets, together with copious radiation across the
electromagnetic spectrum. Many galaxies contain supermas-
sive black holes, but in mature galaxies they’ve usually cleared
out most of the matter in their immediate vicinity, making
them visible only through their gravitational effects.
In many ways Centaurus A resembles a normal elliptical
galaxy, but the emissions from its nucleus indicate that it’s
been stirred up by some recent event, likely a collision with
another galaxy. The collision is also presumably responsible
for the extraordinary band of dust that encircles Centaurus
A’s waist. It’s by far the easiest dust band to observe aside
from the Milky Way’s Great Rift, visible through a 6-inch
scope from the southern U.S., and showing intricate detail
through a large telescope if you travel farther south.
Centaurus A is probably a member of the same group as
the spectacular spiral galaxy M83, which lies well to its north.
M83 is centered ¼° north of the Hydra/Centaurus border, so if
you’ve ever viewed it through a telescope at low power, you’ve
seen some of Centaurus’s stars in the same field of view.
The Glorious Hooves
Presumably the idea that Centaurus is a four-footed ani-
mal stemmed from the four brilliant stars near its southern
border: Alpha and Beta Centauri, and Alpha and Beta Crucis.
These stars are sometimes called Rigil Kentaurus, Hadar,
Acrux, and Mimosa, respectively. This is by far the greatest
concentration of fi rst-magnitude stars (magnitude 1.49 and
brighter) in the entire sky.
When Alpha and Beta Crucis were ripped away to form
Crux, the Centaur’s hind legs were left either connected
to preposterously faint stars, as in the Sky & Telescope stick
fi gure on page 22, or dangling in thin air, as shown in
Hevelius’s atlas. If you swing each hind leg forward to line
up with two stars of the Cross, you see the Centaur as the
Greeks did — a dynamic fi gure, with all four legs gathered
under it, ready to spring.
On the other hand, there’s no question that the Southern
Cross is a natural and striking grouping. I see it as a diamond
rather than a Cross, since it lacks a star to mark the intersec-
tion of the upright and horizontal bars. And Epsilon (ε) Cru-
cis, the fi fth-brightest star, fi ts well into the diamond outline
Targets for Telescopes and Binoculars in Centaurus and Crux
Object
Alias Type Distance (l-y) Mag(v) Size/Sep RA Dec.
Rigil Kentaurus Double star 4.37 0.0, 1.3 5.2″ 14 h 39.6 m –60° 50′
1, 2, 3, 4 Centauri Asterism — 4.2–4.7 2.7° 13 h 51.8 m –33° 00′
NGC 5139 Omega Centauri Globular cluster 17,000 3.9 55′ 13 h 26.8 m –47° 29′
NGC 5128 Centaurus A Galaxy 11,000,000 6.8 26′ × 20′ 13 h 25.5 m –43° 01′
NGC 4755 Jewel Box Open cluster 6,400 4.2 10′ 12 h 53.7 m –60° 22′
Acrux Triple star 320 1.3, 1.7, 4.8 4.2″, 90″ 12 h 26.6 m –63° 06′
Alpha Centauri C Red dwarf star 4.24 11.0 — 14 h 29.7 m –62° 41′
Alpha Centauri
Head of Centaurus
Alpha Crucis
Proxima Centauri
Angular sizes and separations are from recent catalogs and papers. Visually, an object’s size is often smaller than the cataloged value. Right ascension and dec-
lination are for epoch and equinox 2000.0; the right ascensions of Alpha and Proxima Centauri have decreased approximately 0.1 m since then. The separation of
Alpha Centauri AB is for epoch 2019.5. The distance given for Centaurus A is a lower limit; the upper limit is around 26,000,000 light-years.
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A PR I L 2 019 • SK Y & TELESCOPE