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Space Topics: Planetary AnalogsStars Above, Earth BelowAstronomy and Space Exploration in America's National Parks
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Receding from the Lake
A century of aerial photography shows the changing face of Portage Glacier. The glacier has almost totally receded from the lake and valley it carved. The position of the terminus in 2007 is roughly at the position of the 1999 edge. Credit: 1914 photo R.P. Strough, 1984 photo Aeromap U.S., (Kennedy et al. 2006, USGS Fact Sheet "A Century of Retreat at Portage Glacier") |
Down the lake, a tour boat will take you out and around that ridge where the glacier, for now, still rests in the water. But even that is changing as recent recession has revealed an enormous chunk of black shore rock right in the middle of the glacier wall. With each passing day in the land of the midnight sun the heat of that exposed rock is only going to further melt the ice. From the boat I watch as water pours down its face and massive chunks of ice calve into the lake.
Receding from the Lake
The terminus of Portage Glacier has finally begun to recede from the lake it formed. Numerous streams of water cascade down the rock face as nearly 20 hours of sunlight warm the newly exposed dark rock. Credit: Tyler Nordgren |
Planets are dynamic places. In my time growing up in the Pacific Northwest, I’ve been fortunate to see the planet change. Some changes were exciting. My father and I pointed our telescope at Mount St. Helens the Sunday morning in May 1980 when the perfect cone I’d always known suddenly became a trapezoid. Years later, I carried off to graduate school a mayonnaise jar full of volcanic ash I shoveled off our driveway. However, the disappearance of a glacier in less than my lifetime leaves me concerned. In the Begich-Boggs Visitor Center there is a display on climate change partially funded by NASA, and in the bookstore I picked up a copy of a book called “Alaska Park Science: Scientific Studies in Climate Change in Alaska’s National Parks” published by the National Park Service. And so my thoughts turn to Venus and Mars.
Glaciers and the National Parks
One of the exhibits in the Begich-Boggs Visitor Center from which the glacier is no longer visible. Credit: Tyler Nordgren |
For those of you checking in on this first entry in my project to facilitate astronomy education through the mechanism of the national parks, the receding glaciers in Alaskan parks along with those in many parks down here in the Lower 48 (Glacier National Park is one of the places I will be visiting in September) serve as an excellent first-hand example of how planetary climates can change. While no one is yet blaming Venus’ runaway greenhouse effect on an early Venusian dependence on fossil fuels, it does serve to show that planetary climates are not set in stone. The very fact that they can change for natural reasons, should lead us to be extra careful that they are not changed accidentally due to unnatural ones.
What once was then, is not now
Viking imagery plus Mars Global Surveyor altimetry data reveal vast and ancient river or outflow channels traveling from Mars' southern highlands to the northern lowlands. The environmental conditions under which these channels could have formed were likely very different from conditions on Mars today. Current Mars exploration is driven, in part, to understand more about this warmer, wetter, period in Martian history. Credit: NASA / JPL / USGS |
While checking out Alaskan glaciers I also spent several nights in Denali National Park. Only a week after the summer solstice the Sun sets to the extreme northwest about 11:30 at night only to rise again in the extreme northeast about four hours later. Between sunset and sunrise is one continuous twilight as the sun never gets more than three degrees (six times its apparent diameter) below the northern horizon. My first night there was full moon. Or at least it should have been.
If the Moon’s orbit was in the same plane as the Earth’s orbit around the Sun, then at full moon it would be exactly 180 degrees away from the Sun in all directions and thus three degrees above the southern horizon. In such a world we would, of course, have lunar and solar eclipses every month as the Moon passed in at out of Earth’s shadow and the Moon’s shadow crossed the face of Earth. This obviously doesn’t happen and the reason is that the Moon’s orbit is tilted by about five degrees with respect to Earth’s orbit. Most months the full Moon glides just above or just below Earth’s shadow in space. As a result of this extra five degrees, the full Moon on June 30th passed below Earth’s shadow (as viewed from my camping spot near the Earth’s north pole) and never passed above the southern horizon. Thus there was a month with a full moon that never rose and never set.
Three nights later, as the Sun made its ever so slight passage beneath the northern horizon, the Moon had moved far enough around in its orbit that it did rise to the south above the mountains of the Alaska Range and yet in its western path it was so low it actually passed horizontally behind the 20,000 ft mass of Denali (Mt. McKinley), the highest peak in North America. I was all set up with my camera, ready to capture this event when clouds rolled in and totally obscured the view. They didn’t part until two hours later when the moon was fully behind the mountain. Such is the life of an observational astronomer.
Two hours too late
The 20,000-foot (6,000-meter) peak of Denali hides the disk of the moon. As an observational astronomer I am constantly playing amateur meteorologist. The unique weather conditions around Denali result in only one in three visitors ever actually seeing it. Had they cleared only a few hours earlier the nearly full moon would have passed horizontally right through my picture. Credit: Tyler Nordgren |
So that’s the first entry. It was a short trip to Alaska. There wasn’t time for any public talks and the astrophotography is obviously limited in a land with no night. Starting in August I will be in Rocky Mountain National Park and then on to Glacier National Park in September. Stay tuned for topics ranging from tectonism and mountain building to the search for extrasolar planets.
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