Australian Sky & Telescope - April 2016__

http://www.skyandtelescope.com.au 53

Swooping3.3°southwestfromZetaleadstothe

openclusterNGC2 3 04,whichmarksthenorthern

pointofanearlyequilateraltriangleitformswith

twogoldenstarstothesouth,magnitudes7and8.

With sides about^1 / 3 °long, the triangle easily fits in a

low-powerfieldofview.Throughmy105-mmrefractor

at 28 ×,theclusterisasmallbutobviousfuzzyspot

setamidastarryfield.Amagnificationof87×picks

out8faintstarflecksglitteringinafoggyglowabout

4 ′across.Throughmy25-cmreflectorat4 3 ×,Iseea

granular haze that’s brighter in the centre, and at 68 ×

thehazebreaksupintoalovelygroupofpinpointstars

spanning 5′.Icount20starsat166×,andatouchof

unresolved haze remains.

Recent professional sources give a diameter of

10 ′forNGC2 3 04,butvisually4′to 5′is a more

reasonable expectation. A study by I

·

nci Akkaya

Oralhan and colleagues (New Astronomy,2015)

indicates that this cluster is about 12,000 light-years

distant and 900,000 years old.

InthestarDelta(δ) Geminorum, also known

as Wasat, we find a true binary star system with a

1, 2 00-year orbit. The components are currently 5.5′′

apart,butthatwillcloseto3. 4 ′′overthenextcentury

andahalf.My1 3 0-mmscopeat117×reveals a golden

8th-magnitude companion southwest of the bright,

yellow-white primary.

When Clyde Tombaugh discovered Pluto in 1930, it

wasquiteclosetoDeltainthesky.Hisphotographic

platesmadeonJanuary23rdand29thofthatyear

showed Pluto as a very faint speck that had moved

from about 42′to 34′east-southeast of the star.

Kappa (κ) Geminorum is another double star worth

visiting. The 130-mm refractor at 91×shows a bright,

deep-yellow primary with a much fainter companion

close west-southwest. The stars are well separated at

117 ×, and the companion shines yellow. The bright star

isayellowgiant,whilethedimmeroneismuchlike

ourSun.AscalculatedbyJimKaler,inhabitantsofa

hypotheticalplanetorbitingtheSun-likestarwouldsee

theyellowgiantbrighteningtheirskywithmorelight

than a thousand full Moons.

Cepheid variable

Zeta Geminorum

is an optical

double; its com-

ponents appear

close together

only from our

point of view.

Zeta Geminorum

NGC 2304

E

D

B

A

C

Discovered by

William Herschel

in 1783, open

cluster NGC 2304

appears as a small

but obvious fuzzy

spot through

small scopes.

PETER WIENERROITHER

DAN CROWSON