48 AUSTRALIAN SKY & TELESCOPE JULY 2016“A William
Herschel
discovery,it’sa
wide pair and
easy for small
telescopes.”
L
ibra,theScales,aZodiacal
constellationthatprecedesthe
clawsofScorpiusacrossthe
sky,isourareaoffocusthismonth.
We begin w it h33 Librae(HN28),
whichisfoundnearly6degrees
south-southeast of Alpha Librae.
A William Herschel discovery,
it’sawidepairandeasyforsmall
telescopes, the stars being 6th and
8th magnitudes. Hartung in his
classic observer’s guide noted an
unusual colour combination of
“orange and red” as seen with his
31-cm reflector.
Six degrees southeast from 33
Librae are two doubles in the same
field of view.BU 227is the easier,
accessibletoan80-mmtelescope.
Themiddlestarinalineofthree,
Isawitasaclose,slightlyunequal,
deep yellow pair at 100× with
18cmaperture.Justeastisthe
closer pairHJ 4756,oneofJohn
Herschel’s tighter doubles. Single
at100×,itshowedasafigure-
eightat330×.Thepositionangle
has changed considerably since
discoveryin1835.Along-period
binary,it’sexpectedtoslowly
widen in the future.
Moving southeast,HJ 4774is
west of the 3.6-mag stars UpsilonBeyond the Scorpion’s claws
TacklethisgroupofcolourfuldoublestartargetsinLibra.
(υ)andTau(τ)Librae.With18
cm at 100× it was a moderately
brightyellowishstarwithaneasy,
faintercompanion,makingupthe
John Herschel pair, discovered
in 1834. In 1889 Sherburne
Wesley Burnham, using the Lick
Observatory’s 36-inch (0.9-m)
refractor, found that the brighter
star was a close pair,BU 1114,
at only 0.65 ̋separation. The
separation gradually increased after
discovery, to about 1.0 ̋by 1910,
remaining there until 1968. After
that it slowly decreased to 0.75 ̋by
1998;thenmorerapidly,to0.43 ̋
in 2009 and 0.32 ̋in 2014. Back
in 1998 using an 18-cm refractor
IwasabletoresolveBU1114into
averyclose,slightlyuneven
double.Itwouldnowrequirea
larger aperture even to see the pair
elongated. Because the position
angle has been pretty constant
over125yearswearelikelyseeing
the orbit from nearly edge on. We
don’tknowwhenBU1114willstart
widening again, as there has not
yet been an orbit calculation.
Nearly 9 degrees north from
HJ 4774 isS672.Suitablefor
small telescopes, the magnitude
6and9starsareataneasy11 ̋separation.Ithasremainedfixed
since discovery by Sir James South
in1825.With18cmat100×the
coloursappearedaspaleyellowand
dullbrownish;anattractivepair.
Two degrees east and just north
from it,BU 122is ½-degree west
of Kappa (κ)Libraeand½-degree
southeastof41Librae.Anear-equal
pair of fairly bright yellowish stars,
and attractively close at 100×, it’s
observable with 80 mm, though
100mmisbetter.Star Name R. A. Dec. Magnitudes Separation PositionAngle MeasureDate of Spectrum
33Lib(HN28) 14 h57.5m -21° 25 ́ 5.9, 8.2 25.7 ̋ 306° 2014 K5V+M2V
BU 227 15 h19.2m -24° 16 ́ 7.5, 8.6 1.8 ̋ 159° 2014 K1III
HJ 4756 15 h19.7m -24° 16 ́ 7.9, 8.3 0.6 ̋ 237° 2013 F4V
HJ 4774 15 h29.0m -28° 52 ́ AB,C 7.0, 9.6 9.5 ̋ 010° 2013 F6IV
BU 1114 " " AB 7.0, 7.8 0.3 ̋ 317° 2014 "
S672 15 h31.7m -20° 10 ́ 6.3, 8.9 11.1 ̋ 281° 2013 A8V
STF 1962 15 h38.7m -08° 47 ́ 6.4, 6.5 11.6 ̋ 189° 2014 F8V+F8V
BU 122 15 h39.9m -19° 46 ́ 7.7, 7.7 1.8 ̋ 228° 2011 F5V
BU 35 15 h42.8m -16° 01 ́ 7.3, 8.7 1.7 ̋ 109° 2012 F7IVDouble star targets in Libra
Data from theWashington Double Star CatalogROSS GOULD
is an experienced
observer of
the southern
skies. He can
be reached at
rgould1792@
optusnet.com.auNearly 4 degrees north and just
east from BU 122, about ½-degree
southwest of Eta (η) Librae, is BU
35. With 18 cm it was barely double
at 100×, though at 180× it became
an easy, uneven close pair, both
stars yellowish and with two very
wide fainter companions. With
quite unequal stars fairly close,
I’d suggest using 100 mm aperture
or more.
Finally, STF 1962 is well to
the north, 5.5-degrees east from
Beta Librae. It’s an equal pair of
yellowish 6th-magnitude stars at
an easy separation. Sissy Haas in
her book Double Stars for Small
Tel escopes describes it, as observed
with only 60 mm, as “a close bright
pair inside a neat triangle of fainter
stars...” Worth visiting. ✦Celestial Calendar