Star transit

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Star transits (Reticle 2deg, magnif. ~10, two stars passing the vertical thread). Timing accuracy may be +-0,5 s. StarTransit-Reticle2deg-21vul.png
Star transits (Reticle 2°, magnif. ~10, two stars passing the vertical thread). Timing accuracy may be ±0,5 s.

A star transit is the passage of a star across the field of view of a telescope eyepiece.

Field of view

The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.

Telescope Optical instrument that makes distant objects appear magnified

Telescopes are optical instruments that make distant objects appear magnified by using an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses. They found use in both terrestrial applications and astronomy.

Eyepiece type of lens attached to a variety of optical devices such as telescopes and microscopes; usually the lens that is closest to the eye when someone looks through the device, placed near the focal point of the objective to magnify the image

An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.

The precise observation of star transits is the basis of many methods in astronomy and in geodesy. The measurements can be done in different ways:

Astronomy natural science that deals with the study of celestial objects

Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets; the phenomena also includes supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, which is the study of the Universe as a whole.

Geodesy The science of the geometric shape, orientation in space, and gravitational field of the Earth

Geodesy, is the earth science of accurately measuring and understanding the Earth's geometric shape, orientation in space, and gravitational field. The field also incorporates studies of how these properties change over time and equivalent measurements for other planets. Geodynamical phenomena include crustal motion, tides, and polar motion, which can be studied by designing global and national control networks, applying space and terrestrial techniques, and relying on datums and coordinate systems.

  1. visually (mostly up to 1990): accuracy 0,1" to 2" (depending on the instrument); timing with digital clocks about 0,05–0,2 seconds
  2. by CCD and other electro-optical sensors: as above, time often better
  3. semi automatic instruments: Photography or "impersonal micrometer", ca. 2 times better than No.1
  4. by Scanning methods: Astrometry satellites like Hipparcos about 0,01".

See also

Precision is a description of random errors, a measure of statistical variability.

Instrument error refers to the combined accuracy and precision of a measuring instrument, or the difference between the actual value and the value indicated by the instrument (error). Measuring instruments are usually calibrated on some regular frequency against a standard. The most rigorous standard is one maintained by a standards organization such as NIST in the United States, or the ISO in European countries. However, in physics—precision, accuracy, and error are computed based upon the instrument and the measurement data. Precision is to 1/2 of the granularity of the instrument's measurement capability. Precision is limited to the number of significant digits of measuring capability of the coarsest instrument or constant in a sequence of measurements and computations. Error is ± the granularity of the instrument's measurement capability. Error magnitudes are also added together when making multiple measurements for calculating a certain quantity. When making a calculation from a measurement to a specific number of significant digits, rounding must be done properly. Accuracy might be determined by making multiple measurements of the same thing with the same instrument, and then calculating the result with a certain type of math function, or it might mean for example, a five-pound weight could be measured on a scale and then the difference between five pounds and the measured weight could be the accuracy. The second definition makes accuracy related to calibration, while the first definition does not.

Meridian circle instrument for timing of the passage of stars across the local meridian

The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purpose telescopes mounted so as to allow pointing only in the meridian, the great circle through the north point of the horizon, the north celestial pole, the zenith, the south point of the horizon, the south celestial pole, and the nadir. Meridian telescopes rely on the rotation of the Earth to bring objects into their field of view and are mounted on a fixed, horizontal, east–west axis.

Literature

Karl Ramsayer was a German geodesist and is well known as one of the most important scientists in geodetic astronomy and in electronic navigation.

Geodetic astronomy or astro-geodesy is the application of astronomical methods into networks and technical projects of geodesy.

International Astronomical Union Association of professional astronomers

The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the internationally recognized authority for assigning designations and names to celestial bodies and any surface features on them.

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Astrometry part of astronomy, covers star positions and their movements

Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of the Solar System and our galaxy, the Milky Way.

Stellar parallax apparent shift of position of a nearby star against the background of distant objects during Earths orbital period

Stellar parallax is the apparent shift of position of any nearby star against the background of distant objects. Created by the different orbital positions of Earth, the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at exactly opposite sides of the Sun in its orbit, giving a baseline distance of about two astronomical units between observations. The parallax itself is considered to be half of this maximum, about equivalent to the observational shift that would occur due to the different positions of Earth and the Sun, a baseline of one astronomical unit (AU).

Hipparcos scientific satellite of the European Space Agency

Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permitted the accurate determination of proper motions and parallaxes of stars, allowing a determination of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, this pinpointed all six quantities needed to determine the motion of stars. The resulting Hipparcos Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. Hipparcos' follow-up mission, Gaia, was launched in 2013.

Very-long-baseline interferometry type of astronomical interferometry used in radio astronomy

Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth. The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.

Figure of the Earth mathematical descriptions of Earths complex shape

The figure of the Earth is the size and shape of the Earth in geodesy. Its specific meaning depends on the way it is used and the precision with which the Earth's size and shape is to be defined. While the sphere is a close approximation of the true figure of the Earth and satisfactory for many purposes, geodesists have developed several models that more closely approximate the shape of the Earth so that coordinate systems can serve the precise needs of navigation, surveying, cadastre, land use, and various other concerns.

Naked eye practice of engaging in visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"

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<i>Gaia</i> (spacecraft) European Space Agency astrometric mission

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Lunar distance (astronomy) distance from center of Earth to center of Moon

Lunar distance, also called Earth–Moon distance, Earth–Moon characteristic distance, or distance to the Moon, is a unit of measure in astronomy. It is the average distance from the center of Earth to the center of the Moon. More technically, it is the mean semi-major axis of the geocentric lunar orbit. It may also refer to the time-averaged distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth–Moon distance. The lunar distance is approximately a quarter of a million miles.

Satellite geodesy geodesy by means of artificial satellites

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Atmospheric refraction deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere

Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. This refraction is due to the velocity of light through air, decreasing with increased density. Atmospheric refraction near the ground produces mirages. Such refraction can also raise or lower, or stretch or shorten, the images of distant objects without involving mirages. Turbulent air can make distant objects appear to twinkle or shimmer. The term also applies to the refraction of sound. Atmospheric refraction is considered in measuring the position of both celestial and terrestrial objects.

Spherical astronomy or positional astronomy is the branch of astronomy that is used to determine the location of objects on the celestial sphere, as seen at a particular date, time, and location on Earth. It relies on the mathematical methods of spherical geometry and the measurements of astrometry.

ELODIE was an echelle type spectrograph installed at the Observatoire de Haute-Provence 1.93m reflector in south-eastern France for the Northern Extrasolar Planet Search. Its optical instrumentation was developed by André Baranne from the Marseille Observatory. The purpose of this instrument was extrasolar planet detection by the radial velocity method. This instrument was also used for the M-Dwarf Programmes.

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Methods of detecting exoplanets

Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the extrasolar planets reported as of April 2014 have been observed directly, with even fewer being resolved from their host star.

Star position

Star position is the apparent location of any given star in the sky, which seems fixed onto an arbitrary sphere centered on Earth. The location is defined by a pair of angular coordinates relative to the celestial equator: right ascension (α) and declination (δ). This pair based the equatorial coordinate system.

Transit instrument astronomical instrument

In astronomy, a transit instrument is a small telescope with extremely precisely graduated mount used for the precise observation of star positions. They were previously widely used in astronomical observatories and naval observatories to measure star positions in order to compile nautical almanacs for use by mariners for celestial navigation, and observe star transits to set extremely accurate clocks which were used to set marine chronometers carried on ships to determine longitude, and as primary time standards before atomic clocks. The instruments can be divided into three groups:

VINITI Database RAS is a database provided by the All-Russian Institute for Scientific and Technical Information (VINITI). The database is devoted to scientific publications. It is described as a large abstracting database. In general, it is indexed for the natural sciences, exact sciences, and technical sciences. Included in this database is AJ, indexed from 1981 to the present day.

Warkworth Radio Telescope

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