Sky and Telescope - June 2018 - 68

Cosmic Voyage

Soaring alone in the
uncrowded constellation
Hercules, the globular
cluster M13 shines
down from a distance of 22,000
light-years. The
softly golden
light of M13 may
look warm, but
it comes to us
from a time when
Earth was anything but. Twentytwo thousand years
ago the world was in
the grip of an Ice Age
glacial maximum. North
Dakota was buried under two
miles of ice, and glacial gouges can
still be seen on boulders in New York's
Central Park.
M13 is one of the closest and
brightest globular clusters visible in
the northern sky. At the other end
of the scale, NGC 2419 (Caldwell
25), the "Intergalactic Wanderer"
in the constellation Lynx, is the
most distant of the Milky Way's
star clusters. Its look-back time
of 275,000 years corresponds to
the oldest evidence of anatomically

The Lagoon
Nebula

8

modern humans. Both genetic dating and new fossils from
Jebel Irhoud in Morocco have pushed the origin of Homo
sapiens to 250,000 to 300,000 years ago. Our ancestors would share the world with other humans -
Neanderthals, Denisovans, and tiny Homo floresiensis - until only 40,000 to 50,000 years ago.
Our last step took us 10 times farther out
than the one before. Now we leap more than
100 times farther, to the Sombrero Galaxy,
M104, in the constellation Virgo, whose light
reaches us from across 31 million light-years.
Thirty-one million years ago, Antarctica was
separating from South America and Australia.
This allowed cold water to circulate all the way
around Antarctica for the first time, and it triggered a period of global cooling. Tropical rainforests contracted to a belt around the equator, and the
first grasslands appeared. New animals evolved
to take advantage of the open plains,
including camels, horses, rhinos, and -
eventually - a family of bipedal apes
with a gift for making tools.
The spiral galaxy NGC 5005
(Caldwell 29), in Canes Venatici, the Hunting Dogs, is our

M11

9

M13

10

THE ICE AGE COMETH As you
observe M13, imagine Earth as it
was 22,000 years ago, when large
w
sheets of ice covered much of
Europe and North America and
mammoths roamed in Mexico.
68

J U N E 2 018 * SK Y & TELESCOPE



Sky and Telescope - June 2018

Table of Contents for the Digital Edition of Sky and Telescope - June 2018

Contents
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