Great Fountain Geyser - 1

Sunset or sundown is the daily disappearance of the Sun below the horizon in the west as a result of Earth's rotation.

The time of sunset is defined in astronomy as the moment the trailing edge of the Sun's disk disappears below the horizon in the west. The ray path of light from the setting Sun is highly distorted near the horizon because of atmospheric refraction, making sunset appear to occur when the Sun’s disk is already about one diameter below the horizon. Sunset is distinct from dusk, which is the moment at which darkness falls, which occurs when the Sun is approximately eighteen degrees below the horizon. The period between sunset and dusk is called twilight.

Locations north of the Arctic Circle and south of the Antarctic Circle experience no sunset or sunrise at least one day of the year, when the polar day or the polar night persist continuously for 24 hours.

Sunset creates unique atmospheric conditions such as the often intense orange and red colors of the Sun and the surrounding sky.

Yellowstone National Park, established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872, is a national park located primarily in the U.S. state of Wyoming, although it also extends into Montana and Idaho. Yellowstone, widely held to be the first national park in the world, is known for its wildlife and its many geothermal features, especially Old Faithful Geyser, one of the most popular features in the park. It has many types of ecosystems, but the subalpine forest is dominant.

Native Americans have lived in the Yellowstone region for at least 11,000 years. The region was bypassed during the Lewis and Clark Expedition in the early 19th century. Aside from visits by mountain men during the early-to-mid-19th century, organized exploration did not begin until the late 1860s. The U.S. Army was commissioned to oversee the park just after its establishment. In 1917, administration of the park was transferred to the National Park Service, which had been created the previous year. Hundreds of structures have been built and are protected for their architectural and historical significance, and researchers have examined more than 1,000 archaeological sites.

The Great Fountain Geyser is a fountain-type geyser located in the Firehole Lake area of Lower Geyser Basin of Yellowstone National Park, Wyoming. It is the only predicted geyser in the Lower Geyser Basin.

The geyser erupts every 9 to 15 hours. Great Fountain's maximum height ranges from about 75 feet (23 m) to over 220 feet (67 m). Its duration is usually about one hour but durations of over two hours have been seen. The duration of an eruption affects the interval that will elapse before the next eruption, so that if the duration of an eruption is recorded, the time of the following eruption can be predicted to a precision of about two hours. The prediction can be refined, to plus or minus 15 minutes or so, through observation of overflow from the crater during the period between eruptions. While this pattern of behavior is observed most of the time, there are occasional episodes of so-called "wild-phase" activity during which the eruptions are of greatly extended duration and intervals between eruptions may be as long as three days. The geyser is then unpredictable until wild-phase activity ceases and more normal eruptions resume.

Nearby White Dome Geyser, which erupts considerably more frequently (albeit less powerfully) from a large geyserite cone, is easily seen from the same parking lot that affords a viewpoint for Great Fountain. The thermophilic bacterium Thermus aquaticus, important because it produces an enzyme used in polymerase chain reaction laboratory procedures central to modern molecular biology, was first isolated from Mushroom Pool, a non-eruptive hot spring a few hundred feet from White Dome Geyser.