Stellar and Astrometric

Look up stellar in Wiktionary, the free dictionary.

Typically, stellar is an adjective referring to one or more stars. See also:

• The Narrabri Stellar Intensity Interferometer was the first astronomical instrument to measure the diameters of a large number of stars at visible wavelengths.
• Stellar abberation is an astronomical phenomenon defined as an apparent motion of the heavenly bodies
• A stellar association is a very loose star cluster, looser than both open clusters and globular clusters.
• Stellar astronomy is the study of stars and the phenomena exhibited by the various forms/developmental stages of stars. Timeline of stellar astronomy
• Stellar atmosphere. Different stars have different atmospheres.
• A stellar black hole is a black hole formed by the collapse of a massive star at the end of its lifetime.
• Stellar cartography. In astronomy, a term used to refer to the mapping of stars, nebula, and other interstellar phonomena.
• Stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics.
• Stellar dynamics is the branch of astrophysics which describes in a statistical way the collective motions of stars subject to their mutual gravity.
• A stellar engine is a hypothetical device that employs a significant part of a star's radiation to generate energy.
• Stellar evolution is the sequence of changes that a star undergoes during its lifetime, the millions or billions of years during which it emits light and heat.
• Stellar Loussier is a fictional character in the anime series Gundam SEED Destiny.
• Stellar magnitude. The apparent magnitude (m) of a star, is a measure of its apparent brightness; that is, the amount of light received from the star.
• Stellar navigation
• Stellar near-collision
• Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements.
• Stellar parallax is the change of angular position of two stars relative to each other as seen from earth, due to the different orbital positions of the Earth.
• Stellar population. Stars can be grouped into two general types called Population I and Population II.
• Stellar spectra/Stellar spectroscopy
• Stellar Stone LLC, a Russian game developer.
• Stellar structure
• Stellar system is a grouping of one or more stars, with (sometimes) non-stellar planetary systems, having a common centre of gravity.
• Stellar uplifting refers to the theoretic prospect of converting lifeless stellar matter into intelligent and sentient substrate.
• Stellar wind. A solar wind is a stream of charged particles (i.e., a plasma) which are ejected from the upper atmosphere of a star.
• The Combination of Stellar Influences is a significant astrological reference and research text.
• The Mooseheart Faith Stellar Groove Band was a Los Angeles based rock band, who operated their own record label, now defunct, called Stellar Records.
• Hyundai Stellar, a car built by Hyundai Motor Company.

Illustration of the use of optical wavelength interferometry to determine precise positions of stars. Courtesy NASA/JPL-Caltech.

Astrometry is a branch of astronomy that deals with the positions of stars and other celestial bodies, their distances and movements.

It is one of the oldest subfields of the science, the successor to the more qualitative study of positional astronomy. Astrometry dates back at least to Hipparchus, who compiled the first catalogue of stars visible to him and in doing so invented the brightness scale basically still in use today. Modern astrometry was founded by Friedrich Bessel with his Fundamenta astronomiae, which gave the mean position of 3222 stars observed between 1750 and 1762 by James Bradley.

Apart from the fundamental function of providing Astronomers with a reference frame to report their observations in, astrometry is also fundamental for fields like celestial mechanics, stellar dynamics and galactic astronomy. In observational astronomy, astrometric techniques help identify stellar objects by their unique motions. It is instrumental for keeping time, in that UTC is basically the atomic time synchronized to Earth's rotation by means of exact observations. Astrometry is also involved in creating the cosmic distance ladder because it is used to establish parallax distance estimates for stars in the Milky Way.

Advances in astrometry

• Sundials were effective at measuring time.
• Astrolabes were invented for measuring celestial angles.
• Astrometric applications led to the development of spherical geometry
• Careful measurement of planetary motions by Tycho Brahe, followed by analysis by Johannes Kepler proved the Copernican principle, that Earth revolves about the Sun.
• The sextant dramatically improved measurement of celestial angles.
• James Bradley measured stellar aberration with a precise transit telescope.
• The development of charge coupled devices (CCDs), and their adoption by astronomers in the 1980s, improved the precision of professional astrometric work.
• The development of inexpensive CCDs, software, and telescopes allowed for large-scale amateur astrometric observation of minor planets.
• From 1989 to 1993, the European Space Agency's Hipparcos satellite performed astrometric measurements resulting in a catalogue of positions accurate to 20-30 milliarcsec for over a million stars.

Astronomers use astrometric techniques for the tracking of near-Earth objects. It has been also been used to detect extrasolar planets by measuring the displacement they cause in their parent star's apparent position on the sky, due to their mutual orbit around the center of mass of the system. NASA's planned Space Interferometry Mission (SIM PlanetQuest) will utilize astrometric techniques to detect terrestrial planets orbiting 200 or so of the nearest solar-type stars.

Astrometric measurements are used by astrophysicists to constrain certain models in celestial mechanics. By measuring the velocities of pulsars, it is possible to put a limit on the asymmetry of supernova explosions. Also, astrometric results are used to determine the distribution of dark matter in the galaxy.

Astrometrics

Astrometrics is the science of stellar measurements and motion. Astrometrics was used, during the 1990s, to detect extrasolar gas giants orbiting various solar systems. This was done by observing the "stellar wobble" of a star and calculating what kinds of gravitational forces would cause such motion; it was then determined that planetary forces must be affecting the stars in question.

Other references

In the fictional Star Trek: Voyager, the Astrometrics lab is the set for various scenes.

See also

• Astrometric binary
• Gaia Probe (ESA -- Planned for 2009-14)
• Hipparcos Space Astrometry Mission (ESA -- 1989-93)
• Spherical astronomy