In January 1994, a 6.7-magnitude earthquake
knocked out power in Los Angeles. In the following hours, emergency services
fielded an alarming number of phone calls from people asking if the big silvery cloud
hovering in the night sky somehow caused the quake. They were referring to the Milky Way. Which is maybe a little sad on several levels,
but not all that surprising. About two-thirds of Americans, and half of
all Europeans, can no longer see our own galaxy in the night sky. Why? Light pollution. It started innocently enough, eons ago, with
fire, and then oil lamps and candles, and then, not too long ago, electricity. Since the first electric street lights appeared
in the late 1870s, our world, indoors and out, has been awash in the glow of artificial
light. At this point it’s so ubiquitous that most
of us don’t even notice it until it suddenly goes out. Today we’ve got lights rigged everywhere
-- buildings, billboards, streetlights, stadiums, yards, and parking lots. If you live in a city or even a suburb, it
can be hard to find any real darkness these days, let alone look up and see many stars. Of course artificial light isn’t evil. It’s awesome. We all use it; it’s done a lot for us. That’s why we invented it and pay lots of
money for it. But much of our outdoor artificial lighting
has made life more difficult -- and not just for frustrated astronomers and light sleepers. We’re starting to see just how dangerous
light pollution can be to our environment, our wildlife, and even our own health. [INTRO] Light pollution! Let’s define it as the adverse effects of
excessive artificial light, and it comes in lots of different forms. Urban sky glow, for example, is the overall
brightening of the night sky, caused by light being scattered by water or particles in the
air. It’s that bright halo that appears over
cities at night and keeps urbanites from seeing stars. According to the International Dark-Sky Association,
LA’s skyglow can be seen from an airplane 200 miles away. Light trespass, meanwhile, happens when artificial
light falls where it is unwanted, like how your neighbor’s floodlight shines directly
onto your otherwise nice and dark pillow. Glare occurs when super-bright lights aren’t
properly shielded and shine horizontally. It decreases visibility and even be dangerously
blinding at times. And finally there’s clutter, the general
bright, bombastic, and over-the-top combination of various light sources in over-lit urban
areas. Think like the Las Vegas Strip, or Manhattan. Clutter contributes to urban sky glow, light
trespass, and glare, and just demolishes any nighttime ambiance. You can measure a landscape’s night-sky
brightness, astronomical observability, and light pollution using an assessment scale
called the Bortle Scale. John E. Bortle created the scale in 2001 to
help amateur astronomers compare stargazing spots. The scale ranges from one to nine, one being
the darkest of wilderness skies, and nine being the dense inner-city skies that so frustrate
star-gazers. It’s easy to imagine how light pollution
interferes with our ability to study the sky. All that sky glow projects up as much as it
does down, and it makes it hard to see the more subtle lights and objects in space without
special filters. But all this extra light ruins astronomers’
nights in another way--it messes with their spectrographs. Spectrographs are instruments that record
how an object’s light disperses into different signature color components. If you know how to read a spectrum of a celestial
object, you can determine certain things about it, like its mass, chemical composition, temperature,
luminosity, and just what the heck it is. This makes spectroscopy a vital part of astronomy,
and light pollution mucks it all up, in part because artificial light shows up as bright,
obscuring lines in those spectra. So the light that comes from mercury vapor
lamps, for instance, creates a specific “fingerprint” line associated with mercury, while metal
halide lamps leave markers for halogen gases that they use. These lines break up and obscure the otherwise
smooth spectra we see from celestial objects, and they can be hard to filter out. And as you can imagine, astronomers find this
interference really annoying. But excessive artificial lighting is more
than an irritating variable for scientists -- it’s also a huge energy suck. As much as a quarter of all electricity worldwide
goes to generating light. A 2008 survey in Austria found that public
lighting was the largest source of their government’s greenhouse emissions, accounting for between
30 and 50 percent. Powering the country’s nearly two million
public lights consumed 1,035 Gigawatt hours of electricity and released over a million
tons of CO2 in the process. And we all know how destructive these emissions
are to our environment. But the light itself can also be a very powerful
biological force. If you think back to your last summer night
on the porch, you’ll recall lots of creatures are inherently drawn to light. Many of those animals get burned. Meaning, they die. Many flying insects swarm around streetlights,
which is great for industrious spiders who know where to build a web, but it can throw
off the balance of an entire ecosystem. Bats, for example, have different reactions
to introduced lights-- some won’t cross into the light, while others use it to their
advantage. When some Swiss towns installed new streetlamps,
the European lesser horseshoe bat suddenly vanished, because, scientists think, they
were outcompeted by all the more light-tolerant pipistrelle bats that moved in to hunt insects
drawn to the light. An innate attraction to light can be so strong
that it can sort of mesmerize certain song- and seabirds, who are drawn to searchlights
on land, and the bright gas flares of marine oil rigs. The poor birds circle the lights over and
over until they just drop out of the sky from exhaustion. This seemingly uncontrollable attraction is
known as positive phototaxis, and while there are lots of competing theories about what
causes it, we still don’t understand its origins. Meanwhile, hundreds of species of night-migrating
birds rely on constellations to navigate in the dark, and researchers speculate that bright
lights may short-circuit their internal guidance mechanisms, causing them to smash into lit-up
buildings, radio towers, and even each other and the ground. And, of courses, all that artificial light
can also disrupt organisms’ otherwise precisely timed biological clocks. For a few billion years now, life on earth
has evolved under a steady, dependable day-to-night schedule. Pretty much all plants and animals and even
a lot of microbes have adjusted their activities to the regularity of sunrises and sunsets. But with widespread artificial light, some
birds think spring has come early and start breeding ahead of schedule, or migrate prematurely. Nesting sea turtles, too, seek out the darkest
beaches, which are becoming harder and harder to find. Hatchlings naturally gravitate toward the
bright, reflective ocean, but get easily turned around by the big, bright cabana lights behind
them. I could go on, you guys! Light pollution disrupts the nighttime breeding
choruses of frogs and toads, confuses lovestruck fireflies, makes zooplankton more vulnerable
to fish, and exposes a host of nocturnal animals to predators, limiting their foraging and
mate-finding time. And somewhere on the list is us! Humans need darkness, too. We need that balance of light and dark in
our environment to maintain our circadian rhythm -- the physical, mental, and behavioral
changes within a 24-hour cycle. These rhythms greatly influence our sleep-wake
patterns, body temperature, and the release of hormones! The production of the sleep hormone melatonin
is regulated by a group of nerve cells called the suprachiasmatic nucleus, or SCN, which
sits in the brain just above the optic nerves, so it’s constantly receiving information
about incoming light. When it registers less light, like it usually
would at night, these cells ramp up the melatonin, which leaves you drowsy and ready for bed. But without that signal coming at regular,
somewhat predictable intervals, it can throw the circadian rhythm out of whack. These cycle disruptions have been linked to
sleep disorders, depression, obesity, and seasonal affective disorder. But I think that we can all agree that a lack
of sleep is not that huge a deal, compared to cancer. Several recent studies have suggested that
prolonged exposure to artificial light at night increases the risk of certain types
of cancer, especially breast cancer and other types that require hormones to spread. Some of these studies have shown that women
who work night shifts have higher rates of breast cancer, and in 2007, the International
Agency for Cancer Research classified night work as a “probable human carcinogen.” The good news, if you can see it, is that
of the many, many, MANY forms of pollution we face today, light pollution is one of the
most easily remedied. Simple changes in lighting design, materials,
and zoning could go a long way in limiting the light pointing up into the atmosphere. The International Dark-Sky Association has
developed guidelines to help cities like Flagstaff, Arizona -- the world’s “first international
dark sky city” -- to reduce light pollution. Their tricks include things like shielding
light sources so they point downward, limiting the lumens -- that’s the unit we use to
measure perceived brightness -- that individual lights can emit, and putting caps on the number
of lumens emitted per acre. Even Paris, the City of Lights, now requires
storefronts and office buildings to turn off their lights between 1 and 7 am. Not the Eiffel Tower though, that can stay
on. Standards like these can save communities
a lot of energy, money, and work toward restoring some ecological integrity. Not only that, getting a handle on this pollution
may give us back something vital to humanity-- our ability to look beyond the smallness of
ourselves, out into the infinite beyond. It’s like what Neil de Grasse Tyson once
said, “When you look at the night sky, you realize how small we are within the cosmos. It's kind of resetting of your ego. To deny yourself of that state of mind, either
willingly or unwittingly, is to not live to the full extent of what it is to be human.” Thanks for watching this SciShow Infusion
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Awesome!