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2012.03.24 台北 / 擎天崗 (PS) — Fotopedia
F4 60secs ISO400 * 120 pics + F4 6mins ISO200
Wikipedia Article
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Yangmingshan

The Yangmingshan National Park (Chinese: 陽明山國家公園; pinyin: Yángmíngshān Guójiā Gōngyuán) is one of the eight national parks in Taiwan, located between Taipei City and New Taipei City. The districts that house parts of the park grounds include Taipei's Beitou and Shilin Districts; and New Taipei's Wanli, Jinshan and Sanzhi Districts. During the Japanese occupation era of Taiwan, it was known as Datun National Park (大屯国立公園). The National Park is famous for its cherry blossoms, hot springs, sulfur deposits, fumaroles, venomous snakes and hiking trails, including Taiwan's tallest inactive volcano, Seven Star Mountain (七星山, 1,120 m).


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Pole star

A pole star is a visible star, preferably a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent position is close to one of the celestial poles, and which lies approximately directly overhead when viewed from the Earth's North Pole or South Pole. A similar concept also applies to other planets than the Earth. In practice, the term pole star usually refers to Polaris, which is the current northern pole star, also known as the North Star.

The south celestial pole currently lacks a bright star like Polaris to mark its position. At present, the naked-eye star nearest to this imaginary point is the faint Sigma Octantis, which is sometimes known as the South Star.

While other stars' apparent positions in the sky change throughout the night, as they appear to rotate around the celestial poles, pole stars' apparent positions remain virtually fixed. This makes them especially useful in celestial navigation: they are a dependable indicator of the direction toward the respective geographic pole although not exact; they are virtually fixed, and their angle of elevation can also be used to determine latitude.

The identity of the pole stars gradually changes over time because the celestial poles exhibit a slow continuous drift through the star field. The primary reason for this is the precession of the Earth's rotational axis, which causes its orientation to change over time. If the stars were fixed in space, precession would cause the celestial poles to trace out imaginary circles on the celestial sphere approximately once every 26,000 years, passing close to different stars at different times. However, the stars themselves also exhibit proper motion, and this motion is another cause of the apparent drift of pole stars.


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Polaris

Polaris (α UMi, α Ursae Minoris, Alpha Ursae Minoris, commonly North Star, Northern Star or Pole Star, also Lodestar, sometimes Guiding star) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star.

It is a multiple star, consisting of the main star α UMi Aa, two smaller companions, α UMi B and α UMi Ab, and two distant components α UMi C and α UMi D. α UMi B was discovered in 1780 by William Herschel.


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Long-exposure photography

Long-exposure photography or time-exposure photography involves using a long-duration shutter speed to sharply capture the stationary elements of images while blurring, smearing, or obscuring the moving elements. The paths of moving light sources become clearly visible.


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Night photography

Night photography refers to photographs taken outdoors between dusk and dawn. Night photographers generally have a choice between using artificial light and using a long exposure, exposing the scene for seconds, minutes, and even hours in order to give the film or digital sensor enough time to capture a usable image. With the progress of high-speed films, higher-sensitivity digital image sensors, wide-aperture lenses, and the ever-greater power of urban lights, night photography is increasingly possible using available light.


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Star Trail Photography

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Astrophotography

Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photograph of an astronomical object (the Moon) was taken in 1840, but it was not until the late 19th century that advances in technology allowed for detailed stellar photography. Besides being able to record the details of extended objects such as the Moon, Sun, and planets, astrophotography has the ability to image objects invisible to the human eye such as dim stars, nebulae, and galaxies. This is done by long time exposure since both film and digital cameras can accumulate and sum light photons over these long periods of time. In professional astronomical research, photography revolutionized the field, with long time exposures recording hundreds of thousands of new stars and nebulae that were invisible to the human eye, leading to specialized and ever larger optical telescopes that were essentially big "cameras" designed to collect light to be recorded on film. Direct astrophotography had an early role in sky surveys and star classification but over time it has given way to more sophisticated equipment and techniques designed for specific fields of scientific research, with film (and later astronomical CCD cameras) becoming just one of many forms of sensor.

Astrophotography is a large sub-discipline in amateur astronomy where it is usually used to record aesthetically pleasing images, rather than for scientific research, with a whole range of equipment and techniques dedicated to the activity.


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Celestial pole

The north and south celestial poles are the two imaginary points in the sky where the celestial bodys' axis of rotation, indefinitely extended, intersects the imaginary rotating sphere of stars called the celestial sphere. The north and south celestial poles appear permanently directly overhead to an observer at the celestial body's North Pole and South Pole respectively. As the celestial body spins on its axis, the two celestial poles remain fixed in the sky, and all other points appear to rotate around them, completing one circuit per day (strictly per sidereal day).

The celestial poles are also the poles of the celestial equatorial coordinate system, meaning they have declinations of +90 degrees and −90 degrees (for the north and south celestial poles, respectively).

The celestial poles do not remain permanently fixed against the background of the stars. Because of a phenomenon known as the precession of the equinoxes, the poles trace out circles on the celestial sphere. On Earth, this takes a period of about 25,700 years. The celestial body's axis is also subject to other complex motions which cause the celestial poles to shift slightly over cycles of varying lengths; see nutation, polar motion and axial tilt. Finally, over very long periods the positions of the stars themselves change, because of the stars' proper motions.


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Night sky

The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight, starlight, and airglow, depending on location and timing.

The night sky and studies of it have a historical place in both ancient and modern cultures. In the past, for instance, farmers have used the state of the night sky as a calendar to determine when to plant crops. Many cultures have drawn constellations between stars in the sky, using them in association with legends and mythology about their deities.

The anciently developed belief of astrology is generally based on the belief that relationships between heavenly bodies influence or convey information about events on Earth. The scientific study of the night sky and bodies observed within it, meanwhile, takes place in the science of astronomy.


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Earth's rotation

Earth's rotation is the rotation of the solid Earth around its own axis. The Earth rotates from the west towards the east. As viewed from the North Star or polestar Polaris, the Earth turns counter-clockwise.

The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. This point is distinct from the Earth's North Magnetic Pole. The South Pole is the other point where the Earth's axis of rotation intersects its surface, in Antarctica.

The Earth rotates once in about 24 hours with respect to the sun and once every 23 hours 56 minutes and 4 seconds with respect to the stars (see below). Earth's rotation is slowing slightly with time; thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth's rotation. Atomic clocks show that a modern day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which UTC is adjusted by leap seconds.


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Star trail

A star trail is a type of photograph that utilizes long-exposure times to capture the apparent motion of stars in the night sky due to the rotation of the Earth. A star trail photograph shows individual stars as streaks across the image, with longer exposures resulting in longer streaks. Typical exposure times for a star trail range from 15 minutes to several hours, requiring a 'bulb' setting on the camera to open the shutter for a longer period than is normal.

Star trails have been used by professional astronomers to measure the quality of observing locations for major telescopes.