Australian Sky & Telescope - June 2018

42 AUSTRALIAN SKY & TELESCOPE July 2018

BINOCULAR HIGHLIGHT by Jonathan Nally

T

here is such a wealth of celestial richness in Scorpius for the

binocular user that it’s sometimes hard to know where to begin.

The constellation’s star clusters, nebulae (bright and dark)

and overall background star-field hold the promise of many hours of

enjoyable viewing. One of the standout objects in Scorpius is number 7

on Charles Messier’s famous list of deep sky objects. (It is, in fact, the

southernmost object on his list.) Messier 7 is also catalogued as NGC

6475, but its common name is the Ptolemy Cluster, named after the

2nd century CE astronomer Claudius Ptolemy.

Every astronomer worth their salt has remarked upon the sparkling

gems that make up M7. Ptolemy himself in CE 130 mentioned

the “nebula following the sting of Scorpius,” while John Herschel

described “a brilliant coarse cluster” and Ernst Hartung noted that it

is “a remarkable sight”. Messier called it a “cluster considerably larger

than the preceding” item on his list, M6.

Easily spotted with the naked eye, your binoculars (depending

upon their size) will reveal a scattering of around a dozen stars, while

a telescope will reveal up to about 80. Take the time to gaze into the

cluster’s depths, noting how its component stars seem to float in front

of the Milky Way’s background.

The combined magnitude of M7’s stars is listed at 3.3, which is

why it’s so easy to spot with the naked eye, particularly as it is nice

and high for us southern observers. Astronomers estimate it lies about

800 light-years from Earth, and is heading toward us at a leisurely 14

kilometres per second.

„JONATHAN NALLY loves sweeping up and down the Milky Way

with his 10×50s.

Ptolemy’s

sparkling gems

21

h

SAGITTA

AQUILA

CAPRICORNUS

PISCIS AUSTRIN

M30

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EN

WHEN

EarlyJune 10p.m.

Late June 9 p.m.

Early July 8 p.m.

Late July 7 p.m.

These are standard times.

HOW

Go outside within an hour or

so of a time listed above. Hold

the map out in front of you

and turn it around so the label

for the direction you’re facing

(such as west or northeast) is

right-side up. The curved edge

represents the horizon, and the

stars above it on the map now

match the stars in front of you

in the sky. The centre of the

map is the zenith, the point in

the sky directly overhead.

FOR EXAMPLE: Turn the

map so the label ‘Facing North’

is right-side up. About halfway

from there to the map’s centre

is the bright star Arcturus. Go

out and look north nearly half-

way from horizontal to straight

up. There’s Arcturus!

NOTE: The map is plot-

ted for 35° south latitude (for

example, Sydney, Buenos

Aires, Cape Town). If you’re

far north of there, stars in the

northern part of the sky will be

higher and stars in the south

lower. Far south of 35° the

reverse is true.

ONLINE

You can get a real-time sky chart

for your location at

skychart.skyandtelescope.com/

skychart.php

USING THE

STAR CHART

–1

Star

magnitudes

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1

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