Sky and Telescope - June 2018 - 69
L AGOON NEBUL A: NOAO / AUR A / NSF; M11: N. A . SH A RP / REU PROG R A M / NOAO / AUR A / NSF; M13: N. A . SH A RP / REU PROG R A M / NOAO / AUR A / NSF;
G L ACIER ILLUSTR ATION: LE A H TISCIONE / S&T; NGC 2419: A DA M BLOCK / M OUN T LEM M ON CEN TER / UNIV ERSIT Y OF A RIZON A; SO MBRERO G A L A X Y: N ASA /
ESA / THE HUBBLE HERITAG E TE A M / STSCI / AUR A; OLIGOCENE: JAY M AT TER NES / PUBLIC DO M AIN
next stop. From approximately 69 million light-years away, its
light has traveled to us from the end of the Age of Dinosaurs.
Our mammalian ancestors had been mostly living in trees
and burrows for 160 million years, but astronomy was about
to reach down to Earth and reset the course of evolution. The
impact of a 10-kilometer-wide (6-mile-wide) asteroid in what
is now Mexico's Yucatán Peninsula collapsed global ecosystems, clearing the way for mammals and one surviving line
of dinosaurs - birds - to take over the world.
Our last two targets were spiral galaxies not vastly different from our own. Now we venture out even farther, to visit
the largest galaxy easily visible from Earth.
NGC 4889 (Caldwell 35) is a supermassive elliptical galaxy in Coma
Berenices. The galaxy may be up
to a thousand times the mass of
the Milky Way, and its central
black hole is an estimated
21 billion solar masses. This
at the center of the
Coma Supercluster of
The Earth of 308 million years ago was dominated
by coal swamps. High levels of
atmospheric oxygen fueled the evolution of giants: dragonﬂies with 27-inch wingspans, millipedes 7 feet long, and
amphibians the size of crocodiles. But the Carboniferous
rainforest collapse of 305 million years ago led to global cooling and drying, conditions which would favor a new group
of animals with drought-resistant scales and hard-shelled
eggs. These were the ﬁrst amniotes, the progenitors of all later
reptiles, dinosaurs, birds, and mammals.
u USHER IN THE SAVANNA Thirty-one million years ago, which is how
far back in time you are looking when you observe M104, grasslands first
appeared and new animals, such as rhinos and horses, began to roam.
In time, tool-wielding bipedal apes would join them.
sk yandtelescope.com * J U N E 2 018