J2000

9C The Ninth Cambridge Catalog of Radio Sources (9C) is an astronomical catalogue of celestial radio sources as measured at 15-GHz. It was published in 2003 by the Cavendish Astrophysics Group of the University of Cambridge. The catalogue was originally made in order to locate radio sources which were interfering with observations using the Very Small Array, but the catalogue has also proved useful for other astronomical programs. Sources are labelled 9CJHHMM+DDMM where HHMM+DDMM are the coordinates in the J2000 system, e.g. 9CJ1510+4138. < ...

Including:

• 9C - External links
• 9C - References

Read more here: » 9C: Encyclopedia - 9C

In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. There are different celestial coordinate systems each using a coordinate grid projected on the celestial sphere, in analogy to the geographic coordinate system used on the surface of the Earth. The coordinate systems differ only in their choice of the fundamental plane, which divides the sky into two equal hemispheres along a great circle. (The fundamental plane of the geographic system is the Earth's equator). Each coordinate system i ...

Including:

• Celestial coordinate system - Converting coordinates
• Celestial coordinate system - Equatorial to Horizontal coordinates

Read more here: » Celestial coordinate system: Encyclopedia - Celestial coordinate system

The aberration of light (also referred to as astronomical aberration or stellar aberration) is an astronomical phenomenon which produces an apparent motion of celestial objects. It is caused by the twin facts that the speed of light is finite, and that an observer on Earth is moving in inertial space. It does not require Earth to carry an observer to some other position after some period of time—only that Earth have some instantaneous velocity. A change in the position of an observer causes parallax ...

Including:

• Aberration of light - Explanation
• Aberration of light - Moving in the rain
• Aberration of light - Types of aberration
• Aberration of light - Annual aberration
• Aberration of light - Diurnal aberration
• Aberration of light - Historical background
• Aberration of light - Search for stellar parallax
• Aberration of light - Bradley's observations
• Aberration of light - Aberration vs nutation
• Aberration of light - Development of the theory of aberration

Read more here: » Aberration of light: Encyclopedia - Aberration of light

Zeta Ceti (ζ Cet / ζ Ceti) is a star in the constellation Cetus. It also has the traditional name Baten Kaitos (Arabic batn qaytus - "belly of the sea monster"). Zeta Ceti is a yellowish star of spectral class K0 IIIBa0.1 and is approximately 260 light years from the Earth. Its apparent magnitude is +3.9. Coordinates for the equinox J2000: Right ascension: 01h 51m 28s

A constellation is a group of stars visibly related to each other in a particular configuration. Constellation - Explanation. In three-dimensional space, most of the stars we see have little relation to one another, but can appear to be grouped on the celestial sphere of the night sky. Humans excel at finding patterns and throughout history have grouped stars that appear close to one another into constellations. An "unofficial" constellation, that is, one that may be widely known but is not recognize ...

Including:

• Constellation - Explanation
• Constellation - History of the Constellations
• Constellation - Constellations in variant cultures
• Constellation - Star names

Read more here: » Constellation: Encyclopedia - Constellation

Theta Leonis (θ Leo / θ Leonis) is a star in the constellation Leo. It also has the traditional names Chertan ("two small ribs") or Chort ("small rib") or Coxa ("hip"). Theta Leonis belongs to the spectral class A0 and has apparent magnitude +3.4. It is 170 light-years from Earth. Coordinates for the epoch J2000: Right ascension: 11h11m35s Declination: +15°42'0" Categories: Leo constellation | Bayer objects ...

Read more here: » Chertan: Encyclopedia - Chertan

Xi Geminorum (ξ Gem / ξ Geminorum) is a star in the constellation Gemini. It also has the traditional name Alzir. Xi Geminorum belongs to spectral class F6 and has apparent magnitude +3.4. It is 64 light years from Earth. Coordinates (J2000): Right ascension: 6h42m30s Declination: +12°57'0" Categories: Gemini constellation | Bayer objects ...

Read more here: » Xi Geminorum: Encyclopedia - Xi Geminorum

In 1992, Wolszczan and Frail discovered that the pulsar has two planets. These were the first extrasolar planets ever discovered; as pulsar planets, they surprised many astronomers who expected to find planets only around main sequence stars. Additional uncertainty surrounded the system, because a claim of an earlier pulsar planet around PSR 1829-10 that had to be retracted due to errors in calculations. Later, an additional planet was discovered. Additionally, this system ...

See also:

PSR 1257+12, PSR 1257+12 - The pulsar, PSR 1257+12 - The planets, PSR 1257+12 - PSR 1257+12 A, PSR 1257+12 - PSR 1257+12 B, PSR 1257+12 - PSR 1257+12 C, PSR 1257+12 - PSR 1257+12 D, PSR 1257+12 - Gas giant

Read more here: » PSR 1257+12: Encyclopedia II - PSR 1257+12 - The planets

Longitude - The search for a solution. The measurement of longitude is important to both cartography and navigation. Historically, the most important practical application of these was to provide safe ocean navigation. Knowledge of both latitude and longitude was required. Whereas latitude was easy to determine by celestial navigation using the elevation of the pole star or of the sun at noon, for longitude early ocean navigators had to rely on dead reckoning. This was inaccurate on long voyages out ...

See also:

Longitude, Longitude - History of the measurement of longitude, Longitude - The search for a solution, Longitude - The Longitude Act and Harrison's chronometer, Longitude - Later developments, Longitude - Ecliptic latitude and longitude, Longitude - Longitude on bodies other than Earth

Read more here: » Longitude: Encyclopedia II - Longitude - History of the measurement of longitude

In three-dimensional space, most of the stars we see have little relation to one another, but can appear to be grouped on the celestial sphere of the night sky. Humans excel at finding patterns and throughout history have grouped stars that appear close to one another into constellations. An "unofficial" constellation, that is, one that may be widely known but is not recognized by the International Astronomical Union, is called an asterism. An example is the grouping c ...

See also:

Constellation, Constellation - Explanation, Constellation - History of the Constellations, Constellation - Constellations in variant cultures, Constellation - Star names

Read more here: » Constellation: Encyclopedia II - Constellation - Explanation

The discovery of the aberration of light in 1725 by James Bradley was one of the most important in astronomy. It was totally unexpected, and it was only by extraordinary perseverance and perspicuity that Bradley was able to explain it in 1727. Its origin is based on attempts made to discover whether the stars possessed appreciable parallaxes. The Copernican theory of the solar system – that the Earth revolved annually about the Sun – had received confirmation by the observations of Galileo and Tycho Brahe (who, however, never accepted heliocentris ...

See also:

Aberration of light, Aberration of light - Explanation, Aberration of light - Moving in the rain, Aberration of light - Types of aberration, Aberration of light - Annual aberration, Aberration of light - Diurnal aberration, Aberration of light - Historical background, Aberration of light - Search for stellar parallax, Aberration of light - Bradley's observations, Aberration of light - Aberration vs nutation, Aberration of light - Development of the theory of aberration

Read more here: » Aberration of light: Encyclopedia II - Aberration of light - Historical background

Note that Julian years in astronomy are purely a unit for measuring time intervals and durations, and are not used as any kind of calendar or timekeeping system. Astronomers do not use the Julian calendar for modern events: when they need to mention a particular date (the date of a solar eclipse for instance), they use the Gregorian calendar like everyone else. However, for events before the introduction of the Gregorian calendar on 15 October 1582, the Ju ...

See also:

Julian year astronomy, Julian year astronomy - Specifying and naming epochs, Julian year astronomy - Reference, Julian year astronomy - External link

Read more here: » Julian year astronomy: Encyclopedia II - Julian year astronomy - Specifying and naming epochs

Because of cool interstellar dust along the line of sight, the Galactic Center cannot be studied at visible, ultraviolet or soft X-ray wavelengths. The available information about the Galactic Center comes from observations at gamma ray, hard X-ray, infrared, sub-millimetre and radio wavelengths. The complex radio source Sagittarius A appears to be located almost exactly at the Galactic Center, and contains an intense compact radio source, Sagittarius A*, which many astronomers believe may coincide with a supermassive black hole at th ...

See also:

Galactic Center, Galactic Center - Proof of existence and location, Galactic Center - Predictions

Read more here: » Galactic Center: Encyclopedia II - Galactic Center - Proof of existence and location

Planetary co-ordinate systems are defined relative to their mean axis of rotation and various definitions of longitude depending on the body. The longitude systems of most of those bodies with observable rigid surfaces have been defined by references to a surface feature such as a crater. The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system (the ecliptic). The location of the prime meridian as well as the position of body's north pole on the celestial sphere may vary with time due to ...

See also:

Longitude, Longitude - History of the measurement of longitude, Longitude - The search for a solution, Longitude - The Longitude Act and Harrison's chronometer, Longitude - Later developments, Longitude - Ecliptic latitude and longitude, Longitude - Longitude on bodies other than Earth

Read more here: » Longitude: Encyclopedia II - Longitude - Longitude on bodies other than Earth

Stellar aberration causes the apparent position of a star to be displaced, and occurs when the observer's motion has a component that is perpendicular to a line between the star and observer. In the diagram to the right, S represents the position of the star, and E the position of the observer on Earth. The true direction of the star relative to the observer is thus ES, whose length represents the speed of light. However, Earth has a velocity in the direction represented by the line EE’, whose length represents ...

See also:

Aberration of light, Aberration of light - Explanation, Aberration of light - Moving in the rain, Aberration of light - Types of aberration, Aberration of light - Annual aberration, Aberration of light - Diurnal aberration, Aberration of light - Historical background, Aberration of light - Search for stellar parallax, Aberration of light - Bradley's observations, Aberration of light - Aberration vs nutation, Aberration of light - Development of the theory of aberration

Read more here: » Aberration of light: Encyclopedia II - Aberration of light - Explanation

As seen from Earth, the pulsar is located in the sky at RA 13 00 01.00, DE +12 40.00 declination, as seen from Earth in the constellation of Virgo, using J2000 coordinates, hence the alternate names PSR 1300+1240 or PSR J1300+1240 (using B1950 coordinates, it would be located at RA 12 57 00, DE +12 00 declination, hence the alternate name PSR B1257+12). It is about 620 parsecs from Earth. PSR 1257+12 was discovered by the Polish astronomer Aleksander Wolszczan in 1990 using the Arecibo radio telescope. It is a mil ...

See also:

PSR 1257+12, PSR 1257+12 - The pulsar, PSR 1257+12 - The planets, PSR 1257+12 - PSR 1257+12 A, PSR 1257+12 - PSR 1257+12 B, PSR 1257+12 - PSR 1257+12 C, PSR 1257+12 - PSR 1257+12 D, PSR 1257+12 - Gas giant

Read more here: » PSR 1257+12: Encyclopedia II - PSR 1257+12 - The pulsar

As seen from Earth, the pulsar is located in the sky at RA 13 00 01.00, DE +12 40.00 declination, as seen from Earth in the constellation of Virgo, using J2000 coordinates, hence the alternate names PSR 1300+1240 or PSR J1300+1240 (using B1950 coordinates, it would be located at RA 12 57 00, DE +12 00 declination, hence the alternate name PSR B1257+12) PSR 1257+12 was discovered by the Polish astronomer Aleksander Wolszczan in 1990 using the Arecibo radio telescope. It is a millisecond pulsar, a kind of neutron st ...

See also:

PSR 1257+12, PSR 1257+12 - The pulsar, PSR 1257+12 - The planets, PSR 1257+12 - PSR 1257+12 A, PSR 1257+12 - PSR 1257+12 B, PSR 1257+12 - PSR 1257+12 C, PSR 1257+12 - PSR 1257+12 D, PSR 1257+12 - Gas giant

Read more here: » PSR 1257+12: Encyclopedia II - PSR 1257+12 - The pulsar

Our current list is based on those listed by the Roman astronomer, Claudius Ptolemy, who lived in Alexandria, Egypt. (Claudius Ptolemy, the astronomer, was not related to the Greek kings of Egypt named Ptolemy.) In more recent times this list has been added to, to fill gaps between Ptolemy's patterns. The Greeks considered the sky as including both constellations and dim spaces between. But Renaisance star catalogs by Johann Bayer and John Fla ...

See also:

Constellation, Constellation - Explanation, Constellation - History of the Constellations, Constellation - Constellations in variant cultures, Constellation - Star names

Read more here: » Constellation: Encyclopedia II - Constellation - History of the Constellations

Ecliptic latitude and longitude are defined for the planets, stars, and other celestial bodies in a similar way to that in which the terrestrial counterparts are defined. The pole is the normal to the ecliptic nearest to the celestial north pole. Ecliptic latitude is measured from 0° to 90° north (+) or south (−) of the ecliptic. Ecliptic longitude is measured from 0° to 360° eastward (the direction that the Sun appears to move relative to the stars) along the ecliptic from the vernal equinox. The equinox at a specific date and time i ...

See also:

Longitude, Longitude - History of the measurement of longitude, Longitude - The search for a solution, Longitude - The Longitude Act and Harrison's chronometer, Longitude - Later developments, Longitude - Ecliptic latitude and longitude, Longitude - Longitude on bodies other than Earth

Read more here: » Longitude: Encyclopedia II - Longitude - Ecliptic latitude and longitude

All modern constellation names are Latin proper names or words, and some stars are named using the genitive of the constellation in which they are found. The genitive is formed using the usual rules of Latin grammar, and for those unfamiliar with that language the form of the genitive is unpredictable and must be memorized. Some examples include: Aries → Arietis; Taurus → Tauri; Gemini → Geminorum; Virgo → Virginis; Libra → Li ...

See also:

Constellation, Constellation - Explanation, Constellation - History of the Constellations, Constellation - Constellations in variant cultures, Constellation - Star names

Read more here: » Constellation: Encyclopedia II - Constellation - Star names