A (6)

J

ustasitisforallastronomers,

variable star observers need to

locate the right field before

looking for a target. In fact, we

have one very special reason —

ifthestarisatitsminimumlight,

itmightnotbevisibleatall.

This month we’ve got a field

that’s hard to top; perfect for

binocularsorsmalltelescopes,

straddling the Galactic equator

andlookinginwardstowardthe

Galactichub.Infact,we’relooking

outfromourLocalArmofthe

MilkyWay,acrossthevoid,and

thensomewayintotheSagittarius-

Carina Arm.

Thechartshowsourmain

target,V905 Scorpii.Italso

shows one globular and six open

Thecentreofattention

Some easy targets in a galactic field that’s bustling with astronomical objects.

star clusters, a dark nebula, and

variable starsBM ScorpiiandRY

Scorpii, which are themselves

worthwhile targets. And there

areplentymoreobjectswe’venot

shown. (The all-sky chart on the

centrepagesofthisissuewillhelp

you place this star field; just look

for the open star cluster M7 and go

from there.)

V905 Sco shines at between

6th- to 7th-magnitude from a few

thousand light-years away. It is an

S Doradus type of variable star,

a class which has long, slow rise

andfalltimesfromminimum

tomaximumlight.They’realso

knownasluminousbluevariables,

or LBVs. I won’t describe them

in detail here because the ‘book’

on these stars is being re-written

evenasyoureadthis,butyou’llget

theideawhenItellyouthatthe

most famous member of the class

isEtaCarinae—big,brightand

unpredictable.

RYScoisaCepheidvariable

withamagnituderangeof7to8

over 20 days, while BM Sco, the

brightest star in M6, is an orange

irregularvariablethatrangesfrom

5th- to 6th-magnitude.✦

ALAN

PLUMMER

observes

from the Blue

Mountains

west of Sydney,

and can be

contacted on

alan.plummer@

variablestars

south.org

Celestial Calendar