Hey smart people, Joe here.
For pretty much all of human history, this
has meant the end of our day. Sure, we harnessed
fire, and some artificial light, but we are
not natural creatures of the night. But now
we’re able to be part of the night like
never before in human history. All thanks
to the invention of the light bulb. Try to
imagine modern life without artificial lighting.
It just isn’t possible.
But… all of that light comes with a dark
side.
On January 17, 1994, a powerful earthquake
struck the Los Angeles area and caused a massive
blackout. Nearby Griffith Observatory started
receiving calls from residents asking about
the strange sky they were seeing. What those
people saw was… the Milky Way. With no artificial
light, the sight of the night sky was so unfamiliar;
they didn’t know what they were looking
at.
Today, more than 80% of the world and more
than 99% of the U.S. and Europe live under
light-polluted skies. A third of humans on
Earth can never see the Milky Way. And places
like Singapore are so polluted by light that
people’s eyes never fully adjust to the
dark.
While researching light pollution the past
couple months, I learned a new word: Scotopic.
It’s the type of vision we use in very low
light levels. Whereas our normal, bright-light
photopic vision is produced by three types
of color-sensitive cone cells, dark scotopic
vision is produced by the eye’s rod cells,
which are great at sensing something’s brightness,
but can’t discriminate different colors.
Anyway, the reason I’d never heard of scotopic
vision before is that most of us don’t experience
it much. Night has been taken over by light.
It still gets dark at night. Unless you’re
near the north or south pole in summer, the
sun still goes down every day. But it’s
not real darkness.
So, then… what is real darkness? I’ve
been struggling for a way to explain it, because
how do you describe the absence of something?
Well, I figure you don’t try describe what’s
missing, you look at what was hiding there
all along.
Now I’m not the world’s best astro-photographer
or anything, but I’ve been lucky enough
to take pictures in some of the darkest places
left in North America: Big Bend National Park.
The Grand Canyon in Arizona. 
And here at McDonald Observatory in West Texas.
And while I was out there, I met someone who’s
trying to save darkness.
I’m Bill Wren, special assistant to the
superintendent at the University of Texas
McDonald Observatory
And my job is to keep the skies dark for
ongoing astronomical research here at the observatory
“The places where you can go to see a naturally
starry sky are vanishing, they’re shrinking,
they’re becoming fewer and farther between.
You have to travel great distances from cities
in order to see a naturally dark sky.”
An amateur astronomer named John Bortle came
up with a scale to measure the night sky brightness
based on how many objects are visible
In perfectly dark skies, Bortle scale 1, there’s
between maybe four and five thousand stars
bright enough to be visible to the naked eye
from any spot on Earth. I used some software
called Stellarium to give you an idea of what
that looks like. It’s actually hard to even
pick out constellations. 
But most Americans live at Bortle scale 5
or higher, which means they aren’t seeing
98% of the stars in the sky.
We see people all the time at our public star parties who have never seen the Milky Way and they’re just awe inspired
Now the beauty of the night sky is one thing,
but there’s a bunch of other reasons we
should protect dark skies.
For astronomy I guess it’s pretty straightforward.
We’ve gotta be able to see the stars in
the sky to do astronomical research. And
there’s other questions about exposure to
too much artificial light at night not being
so good for your health. In fact, it affects
the biorhythms of all living creatures on
the planet.
There’s a cost efficiency question, in terms
of how much light we’re wasting into the
night sky, by poorly designed and poorly installed
light fixtures. On the order of billions
of dollars of electricity are wasted into
the night sky in the US alone. “This is
about dark skies, not dark ground… no reason
to shine it wasted above the horizon and into
the sky”
We’ve lit up streets, parking lots, buildings
and every populated space we can mostly to
make the night more safe.
So when you hear people saying we should use
less light at night, your first reaction might
be “That’ll make us less safe!” right?
But as hard as it is to believe, no study
has ever shown that more light leads to less
crime. Most property crime occurs during the
day. Even the worst crimes, like sexual assaults,
that we normally associate with bad guys in
dark alleys, are far more likely to occur
indoors at the hands of someone the victim
knows. And bad lighting can actually make
bad guys harder to see.
More light at night can actually make us less
healthy too. For hundreds of thousands of
years, humans evolved with the rhythms of
night and day. Like other creatures, we have
a natural biological clock, our circadian
rhythm, that’s controlled by the cycle of
light and dark.
In darkness, our bodies produce a hormone
called “melatonin” that helps us sleep,
boosts our immune system, and helps a bunch
of organs function. Light at night, especially
blue light, can mess with that. And LED lighting,
while it saves energy and money, often peaks
in the blue part of the spectrum, making this
problem worse. Night work has even been classified
by some medical groups as a risk factor for
many cancers.
So consider putting this away at night, and
if you do have to look at a screen, use night
mode or an app to reduce the blue light given
off by your screen.
The more that scientists study this, the more
it looks like we’ve underestimated the negative
effects of light, that it is truly a “pollutant”
in its effect on humans and on wildlife.
There are countless wild species being negatively
affected by our light pollution, whether they
are nocturnal (active at night) or crepuscular
(active during twilight). Everything from
fireflies that can’t find mates to dung
beetles who can no longer navigate by the
Milky Way and from baby sea turtles walking
into roads instead of the sea to millions
of birds killed every year in collisions with
buildings.
Every September 11th in lower Manhattan, 88
7,000 watt searchlights shine into the night
sky as a “Tribute in Light”
It’s one of the brightest light installations
ever constructed, and even though it’s only
on for one night a year, over a million birds
have been lured in by these lights, disrupting
their annual migrations, and many have died
after colliding with buildings. That is, until
scientists started working with the people
running the Tribute in Light to keep that
from happening. Now, if more than a thousand
birds are counted in the lights, they’re
turned off for twenty minutes. You can watch
on this radar image as the lights alternate
between on and off, and huge clouds of disoriented
birds go safely on their way.
I think this is an inspiring example of how
humans and nature can co-exist in a world
of artificial light. Because stopping light
pollution doesn’t mean getting rid of all
artificial light. That’s crazy. Light pollution
is not “all light at night”.
It’s “light out of place”. The reason
satellite views of the dark side of our planet
look like this, is because we’re wasting
that light by shining it up into space, instead
of using it to light our way down here.
Light pollution is unique because it’s the
only kind of pollution we can clean up instantly.
Polluted water and air take decades to cleanse
them of human impacts, but cleaning up the
night skies is easy. Just turn out the light.
“Definitely a sense of awe to stand and
look up at the milky way and see the stars
splashed across the sky, and realize the 3-dimensional,
the depth that you can see when you look into
the plane of the galaxy. Just the scale that
surrounds us, the dimensions of the universe
on the grand scale is just awe-inspiring.”
“I do believe that seeing a naturally dark
sky provides one with a sense of context,
that sense of living in a very large space,
and being part of something on a very grand
scale, and it does give one a sense, just
a thrill. Sometimes a chill up the spine.
To realize that we came out of this universe
as opposed to being put into it… but we
won’t get too philosophical here.”
Well, Bill may not want to get philosophical,
but I think that beautifully sums up why dark
is just as important to our lives as the light.
Now, many of the beautiful shots of the night
sky you’ve seen in this video are time lapses,
made with long-exposure photos that show you
a bit more than you can see with your own
eyes. But I wanted to give you some idea of
what you really can see with the naked eye
under those dark skies so few of us get to
experience.
and while it’s not the crispiest
shot in the world, I hope it captures a feeling
for you…
I’ve been trying to think of a way to describe
what it is like to see this. And it is really
hard to come up with the words. It is something
that you just have to see. And it’s something
that I hope people still get the chance to
see. It makes you feel small and big at the
same time. It makes you feel far away and
connected at the same time. And all I know
for sure is… it’s good for ya.
Stay curious.
Hey. You want more space? PBS is bringing
you the universe with SUMMER OF SPACE, which
includes six incredible new science and history
shows streaming on PBS.org and the PBS Video
app, along with lots of space-y episodes from
PBS Digital Studios creators
Follow me over to AMERICA FROM SCRATCH to
check out their Summer of Space episode on
WHETHER OR NOT WE SHOULD COLONIZE MARS.
Big thank you to McDonald Observatory for
having me out to experience their dark skies.
McDonald Observatory and the International
Dark Sky Association have some fantastic resources
on which types of lighting to minimize wasted
light, and maximize useful light without unintended
effects on wildlife and plants. We’ll put
links to that and a lot more down in the description.
