ES
A^ /
HU
BB
LE
/^ N
AS
A
G
ood things sometimes take a
while. And it’s well to keep that in
mind as we astronomers at mid-north-
ern latitudes wait through the longest
days of the year — and the longest
evening twilights, t oo — for the starry
night to arrive.
By the way, if you’re more than about
50° north of Earth’s equator in June,
you’ll have to wait weeks for full night
to come. The darkest you can get is
astronomical twilight, when the solar
depression angle is between 12° and
18° (that is, the Sun is between 12° and
18° below the horizon). At least you can
look for noctilucent clouds!
In any case, if your sky gets reason-
ably dark by the times listed on the
all-sky map on pages 42–43, you’ll see
beauties well worth waiting for.
From Arcturus to Vega. The fi rst
stars to come out in the June dusk are,
of course, the brightest of this sky —
Arcturus and Vega. Arcturus is usually
classifi ed as a spring star — yet as spring
formally ends and most of us are already
experiencing summer weather and
culture, it’s barely past the meridian on
our map. In the month most associated
with roses, Arcturus is a star that an old
friend of mine once said shines with the
hue of “champagne shot with roses.”
Most remarkably, Arcturus may be —
cue up the old sci-fi thriller movie music
— “the star from another galaxy.” The
highly inclined orbit of Arcturus with
respect to our galaxy’s equatorial disk
was the fi rst clue that the star may have
belonged to a galaxy that collided with,
and was cannibalized by, our Milky Way.Islands
of Night
As spring gives way to
summer, you may have tostay up later to catch celestial
delights. But it’s worth it.While Arcturus is high in the south
on our map, the ever-so-slightly less
bright Vega is already well up the
eastern sky. The other two members
of the Summer Triangle, Altair and
Deneb, are much lower now — certainly
part of their heyday (or should we say
“heynight”?) is in late summer or even
early autumn. If you’re observing in
early June, our map portrays the sky at
11 p.m. and hopefully your personal —
real-life! — version of that sky is dark
enough for you to enjoy two major stops
on the journey between Arcturus and
Vega: the semi-circle of Corona Borealis
and the Keystone of Hercules.
These asterisms are^11 / 3 of the way
and^2 / 3 of the way, respectively, along
the line from Arcturus to Vega. Corona
Borealis is adorned with its 2nd-magni-
tude gem of a star, known as Gemma or
Alphecca. The Northern Crown offers
us legendary variable stars to keep an
eye on and double stars for us to split.
It doesn’t offer us something that the
Keystone does, though: a spectacular
globular cluster. In fact, Hercules holds
the most famous and most-observed
globular cluster of all, M13.Globulars and galaxies — and so
much more. Three of the four great-
est globular clusters visible from
mid-northern latitudes — M13, M3
of Canes Venatici, and M5 of Serpens
— are now all rather near the merid-
ian. (The fourth of the globular greats,
M22, is barely above the horizon as
Sagittarius rises in the southeast.)
But most of us forget that as we begin
the season of globular clusters most
of spring’s bounty of galaxies is still
pretty high (the Virgo Galaxy Cluster,
in particular, is well up in the south-
west, not that far from Arcturus).
Ursa Major is still fairly high, the
front half of Scorpius is creeping
towards the meridian, underappreci-
ated Libra, the Scales, is balanced on
the meridian, and Draco is coiling
(back-half fi rst) towards the meridian.
They’re all part of the start of your visit
to June’s wonderful island of night in
the midst of the ocean of long days. And
this island vacation called June nights is
well worth the wait.¢FRED SCHAAF welcomes your letters
and comments at [email protected].Under the Stars by Fred Schaafskyandtelescope.com • JUNE 2019 45
pANCIENT CLUSTER Messier 5 (M5) is one of the Milky Way’s oldest globular clusters, with most
of its stars clocking in at 12 billion years old or even older. However, astronomers have spotted
young, blue stars in M5, which they think may have arisen through stellar collisions or mass transfer
between binary stars. While scanning the June skies, see if you can spot this globular in Serpens.