user: From the text provided, give me a summary of the most popular attractions in Yosemite National Park.

assistant: <think>
Yosemite Valley represents only one percent of the park area, but this is where most visitors arrive and stay. The Tunnel View is the first view of the Valley for many visitors and is extensively photographed. El Capitan, a prominent granite cliff that looms over Yosemite Valley, is one of the most popular rock climbing destinations in the world because of its diverse range of climbing routes in addition to its year-round accessibility. Granite domes such as Sentinel Dome and Half Dome rise 3,000 and 4,800 feet (910 and 1,460 m), respectively, above the valley floor. The park contains dozens of other granite domes.

The high country of Yosemite contains beautiful areas such as Tuolumne Meadows, Dana Meadows, the Clark Range, the Cathedral Range, and the Kuna Crest. The Sierra crest and the Pacific Crest Trail run through Yosemite, with peaks of red metamorphic rock, such as Mount Dana and Mount Gibbs, and granite peaks, such as Mount Conness. Mount Lyell is the highest point in the park, standing at 13,120 feet (4,000 m). The Lyell Glacier is the largest glacier in Yosemite National Park and is one of the few remaining in the Sierra Nevada.

The park has three groves of ancient giant sequoia (Sequoiadendron giganteum) trees; the Mariposa Grove (200 trees), the Tuolumne Grove (25 trees), and the Merced Grove (20 trees). This species grows larger in volume than any other and is one of the tallest and longest-lived.

Water and ice

The Merced River flowing through Yosemite Valley, a U-shaped valley
The Tuolumne and Merced River systems originate along the crest of the Sierra Nevada in the park and have carved river canyons 3,000 to 4,000 feet (910 to 1,220 m) deep. The Tuolumne River drains the entire northern portion of the park, an area of approximately 680 square miles (1,800 km2). The Merced River begins in the park's southern peaks, primarily the Cathedral and Clark Ranges, and drains an area of approximately 511 square miles (1,320 km2).

Hydrologic processes, including glaciation, flooding, and fluvial geomorphic response, have been fundamental in creating landforms in the park. The park also contains approximately 3,200 lakes (greater than 100 m2), two reservoirs, and 1,700 miles (2,700 km) of streams, all of which help form these two large watersheds. Wetlands in Yosemite occur in valley bottoms throughout the park, and are often hydrologically linked to nearby lakes and rivers through seasonal flooding and groundwater movement. Meadow habitats, distributed at elevations from 3,000 to 11,000 feet (910 to 3,350 m) in the park, are generally wetlands, as are the riparian habitats found on the banks of Yosemite's numerous streams and rivers.


Bridalveil Fall flows from a U-shaped hanging valley that was created by a tributary glacier.
Yosemite is famous for its high concentration of waterfalls in a small area. Numerous sheer drops, glacial steps and hanging valleys in the park provide many places for waterfalls to exist, especially during April, May, and June (the snowmelt season). Located in Yosemite Valley, the Yosemite Falls is the highest in North America at 2,425 feet (739 m). Also in Yosemite Valley is the much lower volume Ribbon Falls, which has the highest single vertical drop, 1,612 feet (491 m). Perhaps the most prominent of the Yosemite Valley waterfalls is Bridalveil Fall, which is the waterfall seen from the Tunnel View viewpoint at the east end of the Wawona Tunnel. Wapama Falls in Hetch Hetchy Valley is another notable waterfall. Hundreds of ephemeral waterfalls can become active in the park after heavy rains or melting snowpack.

All glaciers in the park are relatively small glaciers that occupy areas that are in almost permanent shade, such as north- and northeast-facing cirques. Lyell Glacier is the largest glacier in Yosemite (the Palisades Glaciers are the largest in the Sierra Nevada) and covers 160 acres (65 ha). None of the Yosemite glaciers are a remnant of the Ice Age alpine glaciers responsible for sculpting the Yosemite landscape. Instead, they were formed during one of the neoglacial episodes that have occurred since the thawing of the Ice Age (such as the Little Ice Age). Many Yosemite glaciers, such as the Black Mountain Glacier that was discovered in 1871 and gone by the mid-1980s, have disappeared. Yosemite's final two glaciers – the Lyell and Maclure glaciers – have receded over the last 100 years and are expected by scientists to eventually disappear as a result of natural melting and climate change.</think>
Although Yosemite National Park is perhaps best known for attractions located in the seven square mile Yosemite Valley, the park is quite large and contains popular attractions ranging from groves of giant sequoias, to glaciers and waterfalls, to dozens of granite domes.  The granite domes in particular draw millions of visitors each year, with many attempting to climb them or watch others do so.  Two of the most famous are El Capitan and Half Dome.

user: Why does the time of sunrise vary throughout the year?

assistant: <think>
Although the Sun appears to "rise" from the horizon, it is actually the Earth's motion that causes the Sun to appear. The illusion of a moving Sun results from Earth observers being in a rotating reference frame; this apparent motion caused many cultures to have mythologies and religions built around the geocentric model, which prevailed until astronomer Nicolaus Copernicus formulated his heliocentric model in the 16th century.
Astronomically, sunrise occurs for only an instant: the moment at which the upper limb of the Sun appears tangent to the horizon. However, the term sunrise commonly refers to periods of time both before and after this point:
Twilight, the period in the morning during which the sky is brightening, but the Sun is not yet visible. The beginning of morning twilight is called astronomical dawn.
The period after the Sun rises during which striking colors and atmospheric effects are still seen.
The timing of sunrise varies throughout the year and is also affected by the viewer's latitude and longitude, altitude, and time zone. These changes are driven by the axial tilt of Earth, daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other. The analemma can be used to make approximate predictions of the time of sunrise.
In late winter and spring, sunrise as seen from temperate latitudes occurs earlier each day, reaching its earliest time near the summer solstice; although the exact date varies by latitude. After this point, the time of sunrise gets later each day, reaching its latest sometime around the winter solstice. The offset between the dates of the solstice and the earliest or latest sunrise time is caused by the eccentricity of Earth's orbit and the tilt of its axis, and is described by the analemma, which can be used to predict the dates.
Variations in atmospheric refraction can alter the time of sunrise by changing its apparent position. Near the poles, the time-of-day variation is exaggerated, since the Sun crosses the horizon at a very shallow angle and thus rises more slowly.
Accounting for atmospheric refraction and measuring from the leading edge slightly increases the average duration of day relative to night. The sunrise equation, however, which is used to derive the time of sunrise and sunset, uses the Sun's physical center for calculation, neglecting atmospheric refraction and the non-zero angle subtended by the solar disc.</think>
The timing of sunrise varies throughout the year and is also affected by the viewer's latitude and longitude, altitude, and time zone. These changes are driven by the axial tilt of Earth, daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other.

user: What are the top Sports Movies ever?

assistant: The top sports movies are somewhat subjective but certainly could include the following movies.
1. Miracle
2. Caddyshack
3. The Blind Side
4. Rocky 1
5. The Blind Side
6. Hooziers
7. Slap Shot
8. A field of Dreams
9. Prefontaine
10. Moneyball