34 ASTRONOMY • JUNE 2020
De Vaucouleurs’ classification scheme
was more complex, forming a 3D “cosmic
lemon” that accounted for more proper-
ties of the basic types of galaxies. For spi-
ral galaxies, this included further details
on bars, whether a galaxy showed rings
of encircling material, and how tightly or
loosely wound the arms appeared to be.
De Vaucouleurs also cataloged details
about irregular galaxies and described
peculiar galaxies, which had experienced
galactic train wrecks — interactions with
nearby galaxies that warped their shapes.The incredible scope
of the cosmos
For years, astronomers have quoted the
results of deep galaxy surveys that sug-
gest something like 100 billion galax-
ies exist in the universe. A 2016 studysuggests that the total number of galaxies
could be 2 trillion. But that study looks
back into the early universe, and many
galaxies have merged over time, creating
a smaller “current” number like 100 bil-
lion. We are hanging out in just one of
them, the Milky Way. These basic struc-
tures of the cosmos, like ships f loating
on an ocean of vast darkness, give us a
glimpse beyond our world to understand
the meaning of why we’re here.
As astronomers have discovered more
and more galaxies since the 1920s, they
have acquired one fundamental piece of
knowledge: The universe is really big!
Let’s imagine that you could climb into
a spaceship and travel out into the uni-
verse, seeing more and more distant
things as you went on. Let’s also imagine
that the spaceship could travel at the
speed of light — the fastest speed we
know of in the cosmos. That’s about
186,000 miles per second, the speed at
which photons — particles of light — are
striking your eyes, enabling you to read
this article. (Photons can travel that fast
because they have no mass; spaceships
have mass, so we know that spaceships
couldn’t move that fast. But, for the sakeThe Sunflower Galaxy’s
tightly wound spiral arms
Sometimes called the Sunflower Galaxy, M63
in Canes Venatici lies at a distance of 27 million
light-years. It is bright and is a favorite target for
backyard observers. M63 is a flocculent galaxy
with patchy, indistinct arms. It is also a so-called
LINER galaxy, with an active nucleus powered
by a supermassive black hole. R. JAY GABANYA fireworks galaxy:
Face-on spiral NGC 6946
The speckled face of NGC 6946 in Cygnus, right
on the border with Cepheus, suggests a fireworks
display of color. Bluish spiral arms surround a
yellowish central hub and are speckled with
bright pinkish regions of active star formation.
The galaxy lies at a distance of 22 million light-
years and has frequently served up supernovae —
exploding stars. Ten bright supernovae appeared
in this galaxy between 1917 and 2017.
SUBARU TELESCOPE (NAOJ) AND ROBERT GENDLER