Saving Our SkiesPointing a camera at Earth’s night
side from within the space station, which
orbits Earth at 17,500 miles (28,000 km)
per hour, isn’t easy. Astronauts must com-
pensate for the station’s orbital motion to
avoid trailed images of city lights. NASA
astronaut Don Pettit introduced a barn-
door tracker on board the ISS to cancel
the orbital motion. This enabled him to
take long-exposure photos of Earth’s city
lights and capture details as fi ne as indi-
vidual city blocks without blurring
In 2012, European Space Agency astro-
naut André Kuipers installed NightPod, a
device that automatically tracks individual
objects on Earth. As a result, ISS images
are much more detailed than the famous
Earth at Night photos from the Defense
Meteorological Satellite Program (DMSP)
or even the new “black marble” imagesWASHINGTON, D.C. Many would agree that a lot of things need to be fi xed in Washing-
ton, D.C. Outdoor lighting might not be at the top of the list, but it’s so poorly executed that
the city’s borders are visible at night from space. Although the intense monument lighting on
the National Mall illuminates the night, ISS images show that area to be the darkest in D.C.
aside from the region’s waterways. Washington’s borders are visible because there is essentially
no unshielded lighting in the city, yet shielded lighting is used literally across the street in the
suburbs. The post-top acorn lamps that dominate the D.C. landscape scatter their light in every
direction, making them wasteful and bad sources of glare and skyglow.from the Suomi National Polar-orbiting
Partnership (Suomi NPP) satellite.
Although the astronauts generally
don’t take photos with scientifi c rigor,
their images document the misdirected
light responsible for light pollution. More
thoughtful use of nighttime lighting
would signifi cantly diminish the view
of city lights from space and make our
night skies dark again. To minimize light
pollution at night, outdoor lights should
be pointed downward, used only when
needed, and used only in the amount
that’s needed.
You can download images of indi-
vidual cities from NASA’s Gateway to
Astronaut Photography of Earth web-
site (http://eol.jsc.nasa.gov). You can
even stack frames of nighttime images
together much in the same way you’dcombine images of the Sun, Moon, or
planets to create more detailed pictures.
The results reveal the stunning fact that
city lights vastly outshine the stars even
when viewed from space. It doesn’t have
to be that way. With more responsible
policies, we can limit the footprint of our
lighting, and make the stars easier to see
from the ground and from space. ✦Scott Kardel defends the night as the man-
aging director of the International Dark-Sky
Association (http://darksky.org). Follow
him on Twitter @darkskyscott.28 July 2014 sky & telescope