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Space Topics: Planetary AnalogsStars Above, Earth BelowAstronomy and Space Exploration in America's National Parks
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The Milky Way and Tyler Nordgren Credit: Tyler Nordgren |
by Tyler
Nordgren
March 20, 2008
Standing Tall in the Galaxy
Big Bend National Park -- This wasn’t
in my original plans. I kept telling myself that as I drove over 10 miles
of the worst road I have ever seen in my life down along the Rio Grande
in West Texas. Big Bend National Park is one of the largest national parks
in the Continental U.S., yet it is also one of the least visited. As I
bounced through gullies and climbed over rocks with bone-dry brush scraping
down both sides of my truck I began to see why.
If you’ve ever been to a national park on a moonless night, you’ve
probably seen the Milky Way. For many park visitors, this is an integral part
of their park experience since, according to Chad Moore of the National Park
Service Night Sky Team, 60% of us live in places where the Milky Way is no
longer visible. The lack of light pollution in and around most parks is what
allows us to be able to see the faint stars, nebulosity, and dark interstellar
dust lanes that make the Milky Way so impressive. One of the goals of this
project I’m engaged in is to measure the average sky brightness over
the parks I am visiting and record images of what the sky looks like for the
typical park visitor. How else are we to excite the public in the wonders of
space and space exploration if they can’t see any of it for themselves?
Hubble and Mars Rover images are breathtaking, but an important element of
emotional engagement is lost if one can’t look at the sky and see the
red glow of Mars and know that that is where the rovers currently are.
Light pollution over west Texas
A false-color image of the light visible from space over the western portion of Texas. Pristine, dark skies are in black, while white shows the brightest nighttime light. Interstate highways are shown in blue with red regions denoting national parks and monuments. Big Bend National Park is the large red region along the southern border in the midst of some of the last remaining truly dark skies. El Paso is to the northwest while the San Antonio-Austin-Dallas corridor is to the east. Credit: Chad Moore (NPS) |
Galactic geography
An artist's rendering of our Galaxy. The arms are labeled and yellow arrows indicate sight-lines towards various stars or constellations in our sky. Credit: NASA / JPL-Caltech / R. Hurt (SSC) for underlying galaxy painting |
I have been able to see and photograph the Milky Way from each of the parks I have visited over the last eight months. This is possible because the Milky Way forms a band in the sky that loops completely around the Earth. No matter the time of year, some part of that band is always up in the sky. The Milky Way appears as a band because it is a collection of 100 billion stars (more or less), arrayed in a flat disk. Sitting within this disk, we see the rest of the galaxy as a thin band across the sky. Since we sit in the outskirts of the galaxy, the band looks bigger and brighter in one direction (towards the center of the Galaxy in the direction of Sagittarius) and fainter in the opposite direction (towards the outer reaches of our galaxy in the direction of Taurus the Bull). In summer and fall we look toward Sagittarius at night and the Milky Way is a riot of star clusters, luminous nebulae, and dark, knotty dust clouds. It’s spectacular. In winter and spring we look the other direction and have to be under the darkest of skies in order to make out the dim lights and darks of the Galactic hinterland.
But at this time of year, as spring begins to transition to summer, something amazing happens, especially here down by the southern border in this nearly empty part of the southwest. When I saw I had a free couple weeks in my schedule, I knew I couldn’t pass this up. Starting now, and lasting for about two months, the winter Milky Way sets in late evening while the summer Milky Way rises in early morning. At the transition between the two events, the Milky Way wraps around the horizon, provided you are near a latitude of 27 degrees north and have absolutely no sources of light pollution along the horizon. The darkest place with clean, dry air is right here in Big Bend National Park. Fortunately, the weather at this time of year has the best chance of being good, with clear air blowing out of the north (at other times of year, the wind is more likely to be blowing from other directions, carrying hazy, polluted air that obscures the horizon).
I contacted Rangers Raymond Skiles and Mary Kay Manning of Big Bend who very helpfully found me a camp site in the back country of the park that required, they told me, a high clearance vehicle to get me there. They weren’t kidding. They are very proud of their dark starry skies here and the park newspaper does a great job of advertising the opportunities for stargazing here. The campsite they found for me was 10 miles from the nearest paved road and nearly three miles from the nearest other campsite. On any given day I saw no more than one other car. The sense of isolation was terrific. What was most surprising, though, occurred after dark and took me almost half the night to realize. There was absolutely no source of artificial light anywhere. None. There were no campfires next door to me. There were no street lights down the road. There were no lights of any town or intersection in the distance. There were no cell phone, radio, or TV towers blinking on the horizon. There were no cities over the horizon casting a light dome into the sky. There weren’t even any airplanes in the sky flashing their way from coast to coast (I think this is because Big Bend lies along the Rio Grande at a place where it loops south into Mexico, so any flight overhead would have to pass in and out of U.S. and Mexican airspace). With the exception of one single faint satellite, I did not see a single sign of the Electric Age during my time there. Even in my time in Alaska I could not say the same, as my evenings routinely saw the polar flights of vacationers to and from Europe and Asia.
As the night wore on, the Moon set and the winter Milky Way passed on towards the west. As it set, it grew ever fainter, because its light passed through ever more atmosphere. Finally, near 2:00am, it disappeared completely. At that moment, with the North Galactic Pole, the point directly above the plane of the Galaxy passing overhead, I was standing upright in the Milky Way. Although invisible to the obscuring effects of our atmosphere, I was standing parallel to the rotation axis of the Galaxy. Look to the southeast and I am looking towards the center of the Milky Way. Hold my hands out to both sides and my left points to the direction beyond Cygnus, toward which our Sun is traveling. Towards my right, my hand points to where we have most recently been. Directly above me is the shortest route toward intergalactic space.
The Milky Way and Tyler Nordgren
At 3:30 am I watch the Galaxy rise. Before me is the center of the Galaxy, 8,500 parsecs (30 thousand light years) away. To my left is Cygnus, the direction the Sun travels as it orbits the Galactic center. To my right is the direction from which we have traveled. The Sun makes one complete orbit every 250 million years or so. Notice the Milky Way looks dim and reddened near the horizon. This is due to dust in our atmosphere, just as the light of the rising or setting sun is red and dim. Now, however, it is the light of a billion sunrises. Credit: Tyler Nordgren |
As I stood there marveling at what was only apparent in the mind (darn that atmosphere) the summer Milky Way began to rise. Slowly, a faint glow was apparent before me, where the center of our Galaxy lay nearly 30,000 light years away. Then, silently, the entire eastern horizon became backlit by the pale light of the entire Galaxy. From any other latitude, the light of the Milky Way would have begun at one spot and slowly unraveled as the tilted band rose above the horizon. But here, because of the privileged location of Big Bend National Park, the entire Milky Way rose in unison and just as the Moon appears huge when low upon the horizon with foreground objects to lend it scale, the Milky Way dwarfed mountain and canyon alike. It is an experience I will never forget, and at that moment I knew exactly where I stood in the Galaxy.
Next week, I head to Arches and Canyonlands National Parks. A lot of work has been done in that part of Utah regarding Mars analogs, and I look forward to seeing a little bit of what it must be like to rove across the surface of the Red Planet.
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