Sky and Telescope - June 2015 - 6

Peter Tyson
Spectrum
Founded in 1941
by Charles A. Federer, Jr.
and Helen Spence Federer

Take a Number
Hed.GillSans.30
One of the things i love about astronomy is all the enor-

BOB FRANKE

mous numbers we blithely throw around. We use them, rely on them, wow
ourselves with them, even as we fail in many cases to truly comprehend
the magnitude each represents.
Take a few examples from this issue: A Chinese spacecraft discovers
subsurface layers on the Moon thought be 2.5 to 3.3 billion years old (page
14). Sagittarius A*, the supermassive black hole at the heart of the Milky
Way, has a mass of 4.3 million Suns (page 16). A galaxy cluster called Abell
2065 lies 1.1 billion light-years away (page 60).
We toss such ﬁgures around like so much confetti: 2.5 to 3.3 billion
years ago? Sure. A mass of 4.3 million Suns? No big deal. A galaxy cluster
1.1 billion light-years away? What of it?
What of it? Think about that last one for a moment. How far away is 1.1
billion light-years? It's 6.5 x 1021 miles, or 6,500,000,000,000,000,000,000
miles. Can you really get your mind around that?
I feel reasonably comfortable with the idea of 3,000 miles, the rough
distance across the continental
U.S., having traveled it many times.
I would even venture to say that
I can somewhat grasp the concept
of 239,000 miles, the rounded-up
distance to the Moon. But 93,000,000
miles to the Sun? Forget it. You've
lost me there, much less to Abell
2065. Maybe you're more adept with
huge numbers than I am, but no one
can wrap his or her brain around 1.1
billion light-years.
And that's okay.
I'm reminded of an incident in
The Snow Leopard, by the late Peter
The galaxy cluster Abell 2065 is 1.1 bilMatthiessen. The writer is visiting a
lion light-years away. And that's ﬁne.
Buddhist lama at his isolated hermitage high in the Nepalese Himalaya. Because of crippling arthritis, the monk
has not left his cliﬀ-side haunt in eight years and may never again, yet he
seems happy. Through an interpreter, Matthiessen asks him for his opinion
on his apparent fate. The lama laughs, points dismissively at his lame legs,
and says, "Of course I am happy here! It's wonderful! Especially when I have
no choice!"
We amateurs regularly crunch colossal numbers because they help us
get a grip on what we're dealing with way out there. But we have to admit to
ourselves that they are so whopping as to be essentially absurd. All we can
really do is shake our heads and smile. We have no other choice. A billion
light-years? It's wonderful! ✦

Edi i Chief
Editor in Chi f
6

June 2015 sky & telescope

The Essential Guide
to Astronomy
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Sky and Telescope - June 2015

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