Astronomy

Last month, our topic
was darkness. Let’s
make it a two-parter
and focus now on
light. This makes
sense, for we’re now in the
realm of greatest sun and longest
twilight. If you live north
of latitude 50°, for instance anywhere
in England, full darkness
never happens in June.
The brightness story begins
with photons, the universe’s
most abundant objects.
Contrary to popular belief,
photons have neither luminosity
nor color. They are magnetic
and electrical pulses. You can’t
see magnetism and you can’t
see electricity. So when no one’s
watching, garden roses are not
red, nor is grass intrinsically
green. They’re not even black,
but blank. Photons do deliver
the electromagnetic force,
which triggers some of our cells
to respond electrically, producing
the subjective perception of
light. As physicist Roy Bishop
says in the Observer’s Handbook
from the Royal Astronomical
Society of Canada, a rainbow
occurs strictly inside your skull.
As you gaze at June’s vivid
hues, you’re thus perceiving the
inside of your brain’s occipital
lobe. That’s where your brain’s
100 billion neurons are fashioning
the visual universe. All
brightness and color are created
there. Colors exist nowhere else.
Relatively few are able to
accept this. It seems too far out.
A lifetime of language creates
the illusion that the visual scene
is external to us. So let’s move
on to more comprehensible realities
— like the source of those
photons, the Sun itself.
STRANGEUNIVERSE
BY BOB BERMAN
Attracted by
the light
A solstitial exploration
of brightness
Barring nuclear war, the Sun
is the most brilliant thing we’ll
ever encounter. A supernova
is nine orders of magnitude
brighter, but we’ll never see one
up close, because no star in our
region of the galaxy is massive
enough to pop.
For the most part, the Sun’s
half-degree disk is not the originator
of light-photons. Rather,
the innermost 1/200th of the
solar globe (by volume) is the
solar fusion generator. This
dazzling minuscule sphere in
the Sun’s exact center produces
all the energy. The sharply
defined outer solar layer, the
photosphere, is merely where
light is released. It looks crisp
because it’s just a few hundred
miles thick. This light-emitting
layer is like a veneer, almost
painted onto the solar surface.
The brightness of the Sun is
400 trillion trillion watts. By
the time the light spreads out
and gets here, each square meter
of Earth’s surface (the size of a
wall poster) is illuminated by
about 1,000 watts when the Sun
is overhead. It was just
700 watts when earthly life
began: The Sun keeps getting
more luminous. Each billion
years it’s 7 percent brighter.
Doesn’t sound like much maybe,
but this increase will kill us all
and sterilize the planet within
the next few billion years.
Other suns contribute to the
photon flux. Most are superdim
and orange. To the naked
eye, there’s no trace of 43 of the
50 nearest stars. The night sky
instead displays the oddballs,
the galaxy’s lighthouses. One of
the most luminous marks the
Big Dog’s tail. This is Aludra. It’s
so lovely, two Navy ships were
named for it, as USS Aludra. But
the most famous warm weather
luminary is Deneb, now rising at
nightfall. Each of these powerhouse
stars could be as luminous
as 200,000 suns — but distance
BARRING NUCLEAR WAR,
THE SUN IS THE MOST BRILLIANT THING
WE’LL EVER ENCOUNTER.
BROWSE THE “STRANGE UNIVERSE” ARCHIVE AT www.Astronomy.com/Berman.
plays tricks on astronomers, and
both stars could be much closer,
and therefore dimmer.
So assessing brightness is not
easy. Nothing is obvious. Our
pupils change size while our retinas
photochemically alter their
sensitivity. Would you guess
Full moonlight is 400,000 times
dimmer than sunlight? Would
you ever guess that shiny white
printer paper illuminated by
that Full Moon is actually 2,000
times blacker than a black cat
in sunlight? It’s hard to believe
because Nature protects us from
huge brightness changes. Our
eyes cannot adequately adjust
to two simultaneous scenes that
FROM OUR INBOX
Evolution
On p. 14 in the February 2016 issue, Jeff Hester writes, “But the
only thing guiding evolution in nature is survival. Evolution
by natural selection isn’t moving toward anything.” Obviously,
Hester’s comments are ideological. And he does not tell us what
the guiding mechanism is. Since survival is an effect, what is
the cause? Is it magic? Is it chance (secular miracles)? Or, is survival
of the fittest a result of predetermined laws? There are no
mandates in science that restrict evolution to be without plan or
purpose. Rather, it is Hester’s worldview that rejects purposeful
instruction. This is indeed unfortunate. There are many reasons
for a purpose-driven universe, and we should hope for a more
universal understanding of the scientific evidence, as well as better
education in these matters. — Paul Kursewicz, Epping, New Hampshire
We welcome your comments at Astronomy Letters, P. O. Box 1612,
Waukesha, WI 53187; or email to letters@astronomy.com. Please
include your name, city, state, and country. Letters may be edited for
space and clarity.
have wildly different illumination.
This makes brightness
comparisons non-intuitive.
When telescopically studying
the Sun through appropriate
filters, would we ever guess
that each inky black sunspot,
if it could be seen on its own
in the night sky, would be dazzling
enough to cast shadows?
Or even damage our retina?
In rural unpolluted places,
would we guess that the dark,
“starless” background sky’s
glow is five times brighter than
the combined light of all the
visible stars?
Yet perceiving tiny bits
of light at the very limits of
our senses gives astronomers
a strange satisfaction. Have
you ever seen Uranus with the
naked eye? Late this month
before dawn, Uranus in Pisces
is indeed viewable in unspoiled
skies. Its 6th-magnitude glow
defines the traditional lower
terminus of the human visual
experience, whose upper end is
9 trillion times brighter. That
terminus, marked by our beloved
daystar, now hovers at its annual
high point, in eastern Taurus.
Happy solstice.
Contact me about
my strange universe by visiting
http://skymanbob.com.
8 ASTRONOMY • JUNE 2016