Celestial Calendar
A tempting binocular target
This easy variable star hides right next door to a stellar showpiece
O
ur variable star target this
month is V744 Centauri,
which is comfortably
within the range of 7x50 binoculars
and is very close to one of the great
showpieces of the sky: the globular
cluster Omega Centauri. In fact,
V744 is so close to Omega that
it’s a wonder the star’s variability
went undocumented until 1964.
Ranging from magnitude 4.8 to
6.9 over a period of 90 days, the
star can even be glimpsed by theV744 Cen is located at 3h 39m 59.81s,
–49° 56' 59.0" (epoch J2000). This
chart, which is 8 degrees wide, comes
courtesy of the AAVSO; north is up.
Visual magnitudes are shown with
decimal points omitted to avoid
confusion with faint stars — so 65
denotes a 6.5-magnitude star.naked eye at maximum.
V744 Cen is a semiregular
variable. Members of this class
have been seen to evolve from
shorter-period Cepheid variables —
famously used to estimate cosmic
distances — to more-evolved Mira
variables with larger amplitude and
more regular periods.
To find V744 Cen, first use the
all-sky chart in the centre of this
magazine. Locate Omega Cen at the
northern tip of an isosceles triangle
whose shorter base comprises Beta
Cen and Beta Crucis. Then use
the chart reproduced on this page
to narrow in on the field, and off
you go.Alan Plummer observes from the
Blue Mountains west of Sydney, and
can be contacted on alan.plummer@
variablestarssouth.orgAs Jupiter recedes slightly from
closest approach around its March
8 opposition, its apparent width
will shrink from 44" to 41" during
the rest of March and April.
Below are the times, in Universal
Time, when Jupiter’s Great Red
Spot should rotate across the
planet’s central meridian. The
dates, also in UT, are in bold.
March 15, 4:56, 14:50; 16 , 0:47,
10:43, 20:38; 17 , 6:34, 16:29; 18 ,
2:25, 12:21, 22:16; 19 , 8:12, 18:07;
20 , 4:03, 13:59, 23:54; 21 , 9:51,
19:46; 22 , 5:41, 15:37; 23 , 1:32,
11:28, 21:24; 24 , 7:19, 17:15; 25 ,
3:10, 13:06, 23:02; 26 , 8:57, 18:53;
27 , 4:48, 14:44; 28 , 0:40, 10:35,
20:31; 29 , 6:27, 16:22; 30 , 2:18,
12:13, 22:09; 31 , 8:05, 18:00.
April 1, 3:56, 13:51, 23:47; 2 , 9:42,
19:38; 3 , 5:34, 15:29; 4 , 1:25, 11:21,
21:16; 5 , 7:12, 17:08; 6 , 3:03, 12:59,
22:54; 7 , 8:50, 18:46; 8 , 4:41,
14:37; 9 , 0:33, 10:28, 20:24; 10 ,
6:20, 16:15; 11 , 2:11, 12:07, 22:02;
12 , 7:58, 17:54; 13 , 3:49, 13:45,
23:41; 14 , 9:36, 19:32; 15 , 5:28,
15:23; 16 , 1:19, 11:15, 21:10; 17 ,
7:06, 17:02; 18 , 2:57, 12:53, 22:49;
19 , 8:44, 18:40; 20 , 4:36, 14:31;
21 , 0:27, 10:23, 20:18; 22 , 6:14,
16:10; 23 , 2:05, 12:01, 21:57; 24 ,
7:52, 17:48; 25 , 3:44, 13:39, 23:35;
26 , 9:31, 19:27; 27 , 5:22, 15:18; 28 ,
1:14, 11:09, 21:05; 29 , 7:01, 16:56;
30 , 2:52, 12:48, 22:44.
These times assume that the spot
will be centred at System II longitude
230°. It will transit 1^2 / 3 minutes
earlier for each degree less than
230°, and 1^2 / 3 minutes later for
each degree greater than 230°.
Features on Jupiter appear closer
to the planet’s central meridian
than to the limb for 50 minutes
before and after they transit.JUPITER IN APRIL
ALAN PLUMMER