14 ASTRONOMY • MARCH 2020
STRANGE UNIVERSE
If you enjoy new vocabulary words, you’ll prob-
ably get pleasure from the word subitize. It’s the
ability to immediately perceive how many
objects you’re looking at without counting them. Some
elementary school and kindergarten educa-
tors now utilize the concept, which was first
advocated for in the early 20th century.
Adults generally have no trouble subitiz-
ing up to four objects, and some can do a bit
better. Try it yourself with vitamin tablets or
grapes. If you place three pills on a table, you
won’t have to mentally count out 1-2-3.
Instead, a quick glance instantly tells you
three pills are present.
Try it with four. Then five, which is a bit
harder, and which studies show will delay
your “count” by a quarter of a second. Some
people can subitize higher numbers, but
accuracy normally declines after four.
Patterns can help us cheat when we’re subitizing.
Most famously, the pips on a set of dice are sufficiently
familiar that the majority of us can glance at a die and
immediately distinguish between the face that depicts
four and the face that displays six.
You might already see how this could take us to
astronomical observing. Most of us probably alreadysubitize when we’re setting up for an astro-session. We
may routinely use the same favorite three eyepieces, for
example, and once we’re out in the field, a simple glance
assures us they’re all present. At a public night with a
local astronomy club, a mere glance tells us if four tele-
scopes are pointing at the clouds. But the real usefulness
arrives when we subitize celestial objects.
We immediately perceive if Jupiter is accompanied
by three Galilean satellites, as opposed to all four. And
since one of them — Ganymede — is distinctly brighter
than the others, while only one — Callisto — wanders
more t ha n 10 Jupiter w idt hs f rom t he pla net (a nd i s a l so
the dimmest), we can even “subitize” their identifica-
tions, meaning we grasp it all instantly. OK, you’ve got
to recognize a third moon to identify all four. The easi-
est instant-glance method: Of the remaining two, both
of which are never far from Jupiter, Europa is a discern-
ible 0.3 magnitude dimmer than Io.
Voilà. Instant subitization of the Galilean satellites
and an almost-as-fast identification of each one.
Announce the info to your companions, seem like a
genius, throw your scope back into your SUV, and drive
away. All pointlessly accomplished in 14 seconds.
Under dark skies, the Pleiades beg for your subitizing
skills. Average eyes can see six stars under most subur-
ban conditions. If you already know that six falls within
your subitization skill set, you’re in business. Especially
since here, the pattern provides extra assurance.
Experienced observers know the Pleiades’ outline in
their sleep: It resembles a little dipper. Like pips on a
die, this makes their total number easy to discern and
also lets you instantly spot any additional members that
excellent skies or a recent optometrist visit may turn up.
Where I live, eight stars are always visible
to the naked eye, and spying 11 is not uncom-
mon. The easiest “extra” Pleiad (when using
the singular, you’re supposed to say
“PLEE-ad”) is the star Pleione (“PLEE-oh-
nee”) on the upper left, just above Atlas, the
leftmost bright member. In the always-
enjoyable one-upmanship part of an astro-
meet, you could be the first to claim
subitization of the Seven Sisters.
Probably we all subitize the Hyades too,
whose five main stars and easy V shape make
it a snap. So, let’s at least stretch it to six by
including Lambda (λ) Tauri, the star the
entire V points to li ke a n a rrow. A nd, bingo,
you can’t deny the Hyades are subitizable.
Bet you’ve never read that last sentence anywhere
else. If you have, let us know and we’ll send you a pair
of giant fuzzy dice.How many stars can you count — without counting?
Subitize the sky
How many Pleiades
can you subitize? This
well-known pattern of
stars lets you instantly
determine how many
stars appear to your
peering eyes without
actually counting
them up, one by one.
SERGIY VAKULENKO (FLICKR) Adultsgenerally
have no
trouble
subitizing
up to four
objects, and
some can
do a bit
better.
BY BOB BERMAN
Join me and Pulse
of the Planet’s
Jim Metzner
in my podcast,
Astounding Universe,
at http://www.astounding
universe.comBROWSE THE “STRANGE UNIVERSE” ARCHIVE
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