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32-424: The survey covered 94% of the sky area between the limiting declinations of 63°N and 36°S with a resolution at 1415 MHz of 40 arc minutes in declination. The survey was carried out primarily at a frequency of 1415 MHz but observations were also made at 2650 MHz and 612 MHz. Roughly 19,620 sources were identified over the course of the survey of which 60% were previously uncatalogued. The survey

64-510: A full circle . Astronomers have chosen this unit to measure right ascension because they measure a star's location by timing its passage through the highest point in the sky as the Earth rotates . The line which passes through the highest point in the sky, called the meridian , is the projection of a longitude line onto the celestial sphere. Since a complete circle contains 24 of right ascension or 360° ( degrees of arc ), ⁠ 1 / 24 ⁠ of

96-498: A circle is measured as 1 of right ascension, or 15°; ⁠ 1 / 1440 ⁠ of a circle is measured as 1 of right ascension, or 15 minutes of arc (also written as 15′); and ⁠ 1 / 86400 ⁠ of a circle contains 1 of right ascension, or 15 seconds of arc (also written as 15″). A full circle, measured in right-ascension units, contains 24 × 60 × 60 = 86 400 , or 24 × 60 = 1 440 , or 24 . Because right ascensions are measured in hours (of rotation of

128-656: A net change of   0h. The right ascension of Polaris is increasing quickly—in AD 2000 it was 2.5h, but when it gets closest to the north celestial pole in 2100 its right ascension will be 6h. The North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18 and 6 respectively. The currently used standard epoch is J2000.0 , which is January 1, 2000 at 12:00 TT . The prefix "J" indicates that it

160-547: A particular point measured eastward along the celestial equator from the Sun at the March equinox to the ( hour circle of the) point in question above the Earth. When paired with declination , these astronomical coordinates specify the location of a point on the celestial sphere in the equatorial coordinate system . An old term, right ascension ( Latin : ascensio recta ) refers to

192-403: A two-letter prefix followed by three digits. The first letter, O, stood for Ohio, and the second letter, B–Z inclusive (omitting O) indicated the source right ascension in hours (0–23 inclusive). The first digit indicated the declination zone in increments of 10°, while the last two digits give the source number within the specified region of right ascension and declination. Data reduction for

224-417: Is a Julian epoch . Prior to J2000.0, astronomers used the successive Besselian epochs B1875.0, B1900.0, and B1950.0. The concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC. But Hipparchus and his successors made their star catalogs in ecliptic coordinates , and the use of RA was limited to special cases. With

256-490: Is always a negative number for southern latitudes). An extreme example is the pole star which has a declination near to +90°, so is circumpolar as seen from anywhere in the Northern Hemisphere except very close to the equator. Circumpolar stars never dip below the horizon. Conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earth's surface (except extremely close to

288-455: Is called midnight sun . Likewise, near the local winter solstice, the Sun remains below the horizon all day, which is called polar night . When an object is directly overhead its declination is almost always within 0.01 degrees of the observer's latitude; it would be exactly equal except for two complications. The first complication applies to all celestial objects: the object's declination equals

320-460: Is currently located in the constellation Pisces . Right ascension is measured continuously in a full circle from that alignment of Earth and Sun in space, that equinox, the measurement increasing towards the east. As seen from Earth (except at the poles), objects noted to have 12 RA are longest visible (appear throughout the night) at the March equinox; those with 0 RA (apart from the sun) do so at

352-423: Is given as North Pole Distance (N.P.D.), which is equivalent to 90 – (declination). For instance an object marked as declination −5 would have an N.P.D. of 95, and a declination of −90 (the south celestial pole) would have an N.P.D. of 180. Declination in astronomy is comparable to geographic latitude , projected onto the celestial sphere , and right ascension is likewise comparable to longitude. Points north of

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384-409: Is measured north (positive) or south (negative) of the celestial equator , along the hour circle passing through the point in question. The root of the word declination (Latin, declinatio ) means "a bending away" or "a bending down". It comes from the same root as the words incline ("bend forward") and recline ("bend backward"). In some 18th and 19th century astronomical texts, declination

416-452: Is the celestial equivalent of terrestrial longitude . Both right ascension and longitude measure an angle from a primary direction (a zero point) on an equator . Right ascension is measured from the Sun at the March equinox i.e. the First Point of Aries , which is the place on the celestial sphere where the Sun crosses the celestial equator from south to north at the March equinox and

448-453: Is the complement of right ascension with respect to 24 . It is important not to confuse sidereal hour angle with the astronomical concept of hour angle , which measures the angular distance of an object westward from the local meridian . The Earth's axis traces a small circle (relative to its celestial equator) slowly westward about the celestial poles , completing one cycle in about 26,000 years. This movement, known as precession , causes

480-448: The ascension , or the point on the celestial equator that rises with any celestial object as seen from Earth 's equator , where the celestial equator intersects the horizon at a right angle . It contrasts with oblique ascension , the point on the celestial equator that rises with any celestial object as seen from most latitudes on Earth, where the celestial equator intersects the horizon at an oblique angle . Right ascension

512-413: The equator . Upon flat terrain, the distance has to be within approximately 2 km, although this varies based upon the observer's altitude and surrounding terrain). Generally, if a star whose declination is δ is circumpolar for some observer (where δ is either positive or negative), then a star whose declination is − δ never rises above the horizon, as seen by the same observer. (This neglects

544-402: The poles , declination is uniform around the entire horizon, approximately 0°. Non-circumpolar stars are visible only during certain days or seasons of the year. The Sun's declination varies with the seasons . As seen from arctic or antarctic latitudes, the Sun is circumpolar near the local summer solstice , leading to the phenomenon of it being above the horizon at midnight , which

576-444: The Earth ), they can be used to time the positions of objects in the sky. For example, if a star with RA = 1 30 00 is at its meridian, then a star with RA = 20 00 00 will be on the/at its meridian (at its apparent highest point) 18.5 sidereal hours later. Sidereal hour angle, used in celestial navigation , is similar to right ascension but increases westward rather than eastward. Usually measured in degrees (°), it

608-484: The Earth's Northern Hemisphere , celestial objects with declinations greater than 90° −  φ (where φ = observer's latitude ) appear to circle daily around the celestial pole without dipping below the horizon , and are therefore called circumpolar stars . This similarly occurs in the Southern Hemisphere for objects with declinations less (i.e. more negative) than −90° −  φ (where φ

640-507: The September equinox. On those dates at midnight, such objects will reach ("culminate" at) their highest point (their meridian). How high depends on their declination; if 0° declination (i.e. on the celestial equator ) then at Earth's equator they are directly overhead (at zenith ). Any angular unit could have been chosen for right ascension, but it is customarily measured in hours ( ), minutes ( ), and seconds ( ), with 24 being equivalent to

672-432: The celestial equator have positive declinations, while those south have negative declinations. Any units of angular measure can be used for declination, but it is customarily measured in the degrees (°), minutes (′), and seconds (″) of sexagesimal measure , with 90° equivalent to a quarter circle. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of

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704-491: The celestial sphere. An object at the The sign is customarily included whether positive or negative. The Earth's axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession , causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates (including declination) are inherently relative to

736-453: The coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates (including right ascension) are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch . Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. Right ascension for "fixed stars" on

768-423: The effect of atmospheric refraction .) Likewise, if a star is circumpolar for an observer at latitude φ , then it never rises above the horizon as seen by an observer at latitude − φ . Neglecting atmospheric refraction, for an observer at the equator, declination is always 0° at east and west points of the horizon . At the north point, it is 90° − | φ |, and at the south point, −90° + | φ |. From

800-468: The equator increases by about 3.1 seconds per year or 5.1 minutes per century, but for fixed stars away from the equator the rate of change can be anything from negative infinity to positive infinity. (To this must be added the proper motion of a star.) Over a precession cycle of 26,000 years, "fixed stars" that are far from the ecliptic poles increase in right ascension by 24h, or about 5.6' per century, whereas stars within 23.5° of an ecliptic pole undergo

832-437: The invention of the telescope , it became possible for astronomers to observe celestial objects in greater detail, provided that the telescope could be kept pointed at the object for a period of time. The easiest way to do that is to use an equatorial mount , which allows the telescope to be aligned with one of its two pivots parallel to the Earth's axis. A motorized clock drive often is used with an equatorial mount to cancel out

864-433: The observer's astronomical latitude, but the term "latitude" ordinarily means geodetic latitude, which is the latitude on maps and GPS devices. In the continental United States and surrounding area, the difference (the vertical deflection ) is typically a few arcseconds (1 arcsecond = ⁠ 1 / 3600 ⁠ of a degree) but can be as great as 41 arcseconds. The second complication is that, assuming no deflection of

896-460: The successive Besselian Epochs B1875.0, B1900.0, and B1950.0. A star 's direction remains nearly fixed due to its vast distance, but its right ascension and declination do change gradually due to precession of the equinoxes and proper motion , and cyclically due to annual parallax . The declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity. As seen from locations in

928-425: The survey was done using a computer program developed by John D. Kraus and Robert S. Dixon . The Ohio Sky Survey was published in seven installments and two supplements. Declination In astronomy , declination (abbreviated dec ; symbol δ ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system , the other being hour angle . The declination angle

960-419: The vertical, "overhead" means perpendicular to the ellipsoid at observer's location, but the perpendicular line does not pass through the center of the Earth; almanacs provide declinations measured at the center of the Earth. (An ellipsoid is an approximation to sea level that is mathematically manageable). Right ascension Right ascension (abbreviated RA ; symbol α ) is the angular distance of

992-413: The year of their observation, and astronomers specify them with reference to a particular year, known as an epoch . Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. The currently used standard epoch is J2000.0 , which is January 1, 2000 at 12:00 TT . The prefix "J" indicates that it is a Julian epoch . Prior to J2000.0, astronomers used

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1024-411: Was unique in that it covered a larger portion of the sky, to a greater depth, and at a higher frequency, than any previous survey. In addition, all previously catalogued sources were tabulated and maps of the areas surveyed were included with the positions of all catalogued sources. Sources discovered in the course of the survey were assigned names according to a coordinate numbering system consisting of

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