http://www.skyandtelescope.com.au 49by Alan Plummer VARIABLE STARSThree in Scorpius
R, S and T Scorpius are found in and near Messier 80.
T
his issue we have another
showpiece star field with multiple
observing targets. We looked at
the Carina Nebula back in April 2019
and this time last year it was the open
cluster M7. This month we visit the
environs of the globular star cluster
M80 in Scorpius. Comet hunter Charles
Messier discovered his number 80 in
1781, and described it as a “nebula
without a star... resembling the nucleus
of a comet”. It’s close in the sky to
Antares and the brighter globular
cluster M4.
In 1853 two long-period variable
stars, R and S Scorpii, were discovered
in close proximity to M80 (although
they are not likely to be cluster
members). That these stars were
observed is fortuitous for, in 1860 — to
the delight of the early variable star
observers — a nova of magnitude 6.5
was discovered close to the centre of
the cluster. To my knowledge Nova Sco
1860, or T Sco, is the only classical nova104Action at Jupiter
JUPITER REACHED OPPOSITION in
June and remains visible for most of
the night in the dim southern reaches
of Ophiuchus. Look for it on July 1,
whenits–2.6-magnitudefireblazes
about8½°eastofAntares.Thegas
giantculminatesearliereachnight;by
month’send,it standshighestat about
7:30pmandsinkslowerthroughthe
evening.
Belowarethetimes,inUniversal
Time,whentheGreatRedSpotshould
crossJupiter’scentralmeridian.The
dates,alsoinUT,areinbold.
ThesetimesassumethattheGreat
RedSpotwillbecentredat SystemII
longitude308°.If theRedSpothas
movedelsewhere,it willtransit 12 / 3
minutesearlierforeachdegreelessthan
308°and 12 / 3 minutes later for each
degree more than 308°.
June 1: 3:16, 13:12, 23:07; 2: 9:03,
18:58; 3: 4:54, 14:49; 4: 0:45, 10:41,
20:36; 5: 6:32, 16:27; 6: 2:23, 12:19,
22:14; 7: 8:10, 18:05; 8: 4:01, 13:56,
23:52; 9: 9:48, 19:43; 10: 5:39, 15:34;
11: 1:30, 11:26, 21:21; 12: 7:17, 17:12;
13: 3:08, 13:04, 22:59; 14: 8:55, 18:50;
15: 4:46, 14:42; 16: 0:37, 10:33, 20:28;
17: 6:24, 16:19; 18: 2:15, 12:11, 22:06;
19: 8:02, 17:57; 20: 3:53, 13:49, 23:44;
21: 9:40, 19:35; 22: 5:31, 15:27; 23:
1:22, 11:18, 21:14; 24: 7:09, 17:05; 25:
3:00, 12:56, 22:52; 26: 8:47, 18:43; 27:
4:38, 14:34; 28: 0:30, 10:25, 20:21; 29:
6:16, 16:12; 30: 2:08, 12:03, 21:59.
July 1: 7:55, 17:50; 2: 3:46, 13:41,
23:37; 3: 9:33, 19:28; 4: 5:24, 15:20;
5: 1:15, 11:11, 21:06; 6: 7:02, 16:58; 7:
2:53, 12:49, 22:45; 8: 8:40, 18:36; 9:
4:32, 14:27; 10: 0:23, 10:18, 20:14; 11:
6:10, 16:05; 12: 2:01, 11:57, 21:52; 13:
7:48, 17:44; 14: 3:39, 13:35, 23:31; 15:
9:26, 19:22; 16: 5:18, 15:13; 17: 1: 09,
11:05, 21:00; 18: 6:56, 16:51; 19: 2 : 47,
12:43, 22:38; 20: 8:34, 18:30; 21: 4:25,
14:21; 22: 0:17, 10:12, 20:08; 23: 6:04,
15:59; 24: 1:55, 11:51, 21:47; 25: 7:42,
17:38; 26: 3:34, 13:29, 23:25; 27: 9:21,
19:16; 28: 5:12, 15:08; 29: 1:03, 10:59,
20:55; 30: 6:50, 16:46; 31: 2:42, 12:38,
22:33.ever observed in a globular cluster. Its
location, and those of the other two
variables, are shown on the finder chart
provided.
As you read this S (magnitude range
9.5 to 15.5) should be bright while R
(9.8 to 15.9) will be quite faint. Both
stars can and should be observed once
per week; use the sequence stars shown
on the chart to gauge magnitudes.
Negative observations, ‘fainter than
X’, are good too. Don’t try and go too
faint with S, as there are both 14th-
and 16th-magnitude close companions.
T Sco (6.8 to 21) is today 21st
magnitude; don’t bother with fainter-
than estimates. And by all means keep
an eye on the cluster; it’s thought
that all novae are recurrent, but be
warned, the period might be measured
millennia!■ ALAN PLUMMER observes from the
Blue Mountains west of Sydney, and can
be contacted at [email protected]t R Sco is located
at 16h 17m 39.07s,
–22° 56′ 40.6′′; S Sco
at 16h 17m 40.21s,
–22° 53′ 35.8′′; and
T Sco 16h 17m
02.82s, –22° 58′
33.9′′ (epoch J2000).
This chart (courtesy
of the AAVSO) is
approximately 40
arc minutes across
and has visual
magnitudes shown
with decimal points
omitted to avoid
confusion with
faint stars — so 98
denotes a magnitude
9.8 star.