There are times when it's hard not to take a decent photograph. I encountered one of those moments in early September in the backcountry of Yellowstone Lake in Yellowstone National Park. From a beach in a cove on the lake's Flat Mountain Arm, I watched as the sunset moved almost in slow motion over the glassy waters. Over a period of 10-15 minutes I watched as the sunset lazily ebbed, its rays lighting up the low-hanging clouds with a slowly changing range of hues. And then it was gone.

Gear: Nikon D80, 35-80mm F 5.6, 1/125 sec

Most often we look at the obvious in national parks: gorgeous waterfalls or mountain settings, so-called charismatic mega-fauna such as wolves, bears or moose, colorful wildflowers.

But beyond those scenes and subjects there's an amazing world of life. Since the late 1990s biologists have been involved in an All Taxa Biological Inventory at Great Smoky Mountains National Park. Designed to inventory all the various forms of life in the park, the inventory to date has discovered nearly 900 life forms new to science and 5,000 new to the park.

People often ask me what my favorite national park is, and I always answer Yellowstone. Why? Because it's so rich. You've got incredible wildlife, great mountains, lakes and streams, and, of course, the geothermal resources.

While most geothermal attention seems to go to Old Faithful, there are countless geysers that will impress you with their displays. Jeremy Sullivan nailed this shot of Great Fountain Geyser along Firehole Lake Drive. The backlighting really lends texture and even a little personality to Great Fountain.

There is something about pitching a tent in a national park. It becomes not just your refuge from the weather and bugs, but your home, your comfort zone in the natural world. Is there any more relaxing night than one spent in a tent, preferably gazing through a no-see-um mesh roof so you can watch the stars?

The Rainbow Falls Trail is a long-time favorite in Great Smoky Mountains National Park. In fact, it's thought to be the first route that led to the top of Mount LeConte. Found off the Cherokee Orchard Road just beyond downtown Gatlinburg, the Rainbow Falls Trail follows, and occasional hopscotches, LeConte Creek on the way to the 80-foot waterfall.

Our National Park System is rich in history, not just natural resources. One such example is the statute that recalls a man who had perhaps one of the most significant impacts any one individual could bring to bear on the whaling industry of the early 19th century.

At the New Bedford Whaling National Historical Park on the Massachusetts coast stands a statute in honor of Lewis Temple, an inventor who lived from 1800-1854. His significance? He invented the "toggle iron."

Summer, many will argue, is the season to go camping in the national parks. And, surely, this photo from Cedar Breaks National Monument by Ranger Lee Rademaker supports that argument. The dark, star-punched sky, towering pines, surrounded by the natural world. Can it get any better?

Brooks River Falls in Katmai National Park and Preserve is a popular fishing spot for brown bears, which manage to tolerate close quarters when the salmon are running.

The Cascade Pass Trail is the most popular day hike in North Cascades National Park. According to the park, the trail offers spectacular views of peaks and glaciers. The trail climbs steadily to the pass, with views of peaks such as Eldorado, Johannesburg, Magic, Mixup and McGregor.

This trail provides the shortest and easiest access in the park to the alpine environment. As a result, Cascade Pass is the most popular day hike in the national park and can be quite busy on summer weekends.

These cannons stand today in what is thought to be much the same location as the Union cannonry did on May 3, 1863, when they confronted Confederate cannons 1,200 yards distant atop Hazel Grove.