Sky & Telescope - September 2019 - 45

Under the Stars by Fred Schaaf

Musings on Eternity
The arch of the Milky Way provides the setting for thoughts on the passage of time.
I saw Eternity the other night,
Like a great Ring of pure and
endless light,
      All calm, as it was bright;
And round beneath it, Time in
hours, days, years,
      Driv'n by the spheres
Like a vast shadow mov'd; in
which the world
      And all her train were hurl'd.
-Henry Vaughan,
The World

Cygnus
Star Cloud

Scutum
Star Cloud

Gamma
Scuti
Star Cloud

BOB KING

T

he lines of the poem above are
the most famous penned by the
17th-century Welsh metaphysical poet
Henry Vaughan. The topic of those
lines - and of my column this month
and next - is as much about eternity
as it is for our thoughts when we stare
at the majesty of the Milky Way band
after nightfall at summer's end. But the
topic is also time and the productions
of time - for time and eternity are
inextricably linked.
A ring of pure and endless light.
Vaughan's line about the ring of pure
and endless light brings to mind the
Milky Way band in our sky. Our solar
system lies within the equatorial disk
of the ﬂattened spiral galaxy that is
the Milky Way. So we see a relatively
narrow, heavens-encircling band of
glow that's the combined radiance of
millions of distant stars in the equatorial disk. They're stars that are too faint
from being far away - a few thousand
light-years - for us to see them individually with the naked eye.
Actually, the entire ring of the Milky
Way band is only above the horizon
when it is low along that horizon -
and thus too dimmed by thick air and
haze low in the sky to see properly. In
late summer we see only about half
the ring. But what a half! It arches

high across the evening sky, displaying prominently the brightest of Milky
Way star clouds ever visible from midnorthern latitudes.
As viewed from those latitudes, the
cloud overhead is the Cygnus Star Cloud
(enwreathing the neck and body of Cygnus, the Swan). About halfway to the
southern horizon is the badge of beauty
known as the Scutum Star Cloud. Next
is the bright spot of the little-known
Gamma Scuti Star Cloud (also called
the "Seventh Glow"). Last and lowest
but not least are the Large Sagittarius
Star Cloud and the Small Sagittarius
Star Cloud (the latter is also known as
M24) - puffs of glowing "steam" hanging, respectively, above the spout and
above the lid of the Teapot.
Steppingstones to eternity. Not
even the stars, not even the star clouds,
not even our mighty Milky Way Galaxy
is eternal. However, when we compare
the age of these things to the span of
a human lifetime or human history
we ﬁnd our sights and thoughts take
us stunningly far down the (endless)
road to eternity.

Small
Sagittarius
Star Cloud
Large
Sagittarius
Star Cloud

Much of the Earth's crust is less than
a billion years old (the average age of
the oceans' ﬂoors is some 200 million
years). Remarkably, some of our brightest stars are similarly "young." The Sun
and planets are less than 5 billion years
old. What's the oldest bright star in our
sky? It could be the one low in the west
right after September nightfalls - Arcturus, whose original galaxy may have
collided with ours as much as 8 billion
years ago. The Milky Way Galaxy itself,
whose greater structure we begin to
glimpse in the glowing band these evenings, is perhaps more than 13 billion
years old - as are some of its globular
star clusters, so well represented in the
September evening sky.
Next month: Eternity - Part 2!
All jests aside, next month here we'll
explore the rural area "on the edge of
forever" and the interface of now and
eternity. We'll also discuss just why
it is that "Eternity is in love with the
productions of time."
¢ FRED SCHAAF welcomes your letters
and comments at fschaaf@aol.com.
sk yandtele scope.com * S E P TE M B E R 2 019

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Sky & Telescope - September 2019

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