My first Magazine Sky & Telescope - 04.2019 | Página 24

CONSTE
ers
C
tellati
tellat
Close
up
Centaurus
-
and
Crux
These far-southern constellations rank
near the top in beauty, brightness, and
historical interest.
he ancient Greek constellation Centaurus has always
held a special place in my imagination. One of the
fi rst astronomy facts I ever learned is that Alpha (Į)
Centauri, the constellation’s brightest star, is also the closest
star to the Sun. But to my great sorrow, I soon found out that
I would have to travel at least 800 miles south of my New
York City home to see it.
As I learned more, I became increasingly puzzled by that
fact. A good chunk of Greece lies north of New York City,
and Alpha Centauri is invisible even from Greece’s southern-
most point. So how did this star become part of one of the
ancient Greek constellations?
The answer is that due to precession, the wobble of Earth’s
axis, Alpha Centauri lay farther north in ancient times than
it does now. Earth’s North Pole has been tilting away from
Centaurus at about ½° per century for the last few millennia,
making the constellation ever harder to see from northerly
latitudes. Alpha Centauri was still visible from Athens, Greece,
during its Golden Age around 450 BC. And as precession
pushed the star lower, the center of Greek civilization shifted
south, to Alexandria in Egypt.
T
u CENTAURUS AND CRUX TODAY Constellation stick fi gures became
popular in the 20th century. They are convenient for quick pattern
recognition in light-polluted skies but not always faithful to the traditional
story. Sky & Telescope’s stick fi gure puts Centaurus’s head where the
Greeks visualized his left shoulder.
22
A PR I L 2 019 • SK Y & TELESCOPE
HYDRA
/ 14 h
M68
13 h
M83
4
3
CENTAURUS
–30°
Head of Centaurus
1
2
f
e
s
d
g
i
r
–40°
q +
p
p
`
Omega Centauri
c
_
Centaurus A
a
1
m
b
2
3
4
5
6
¡
LU P US
–50°
l
a
a
Jewel
Box
CIR
`
α
`
/
b
`
Proxima Centauri
CRUX k
α
– 60°
`
TRA
_
a
MUSCA
`
_