Related Research Articles
The astronomical unit is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres or ~8 light minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once each year. The astronomical unit was originally conceived as the average of Earth's aphelion and perihelion; however, since 2012 it has been defined as exactly 149597870700 m.
The ecliptic is the plane of Earth's orbit around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars. The ecliptic is an important reference plane and is the basis of the ecliptic coordinate system.
The term ephemeris time can in principle refer to time in association with any ephemeris. In practice it has been used more specifically to refer to:
- a former standard astronomical time scale adopted in 1952 by the IAU, and superseded during the 1970s. This time scale was proposed in 1948, to overcome the disadvantages of irregularly fluctuating mean solar time. The intent was to define a uniform time based on Newtonian theory. Ephemeris time was a first application of the concept of a dynamical time scale, in which the time and time scale are defined implicitly, inferred from the observed position of an astronomical object via the dynamical theory of its motion.
- a modern relativistic coordinate time scale, implemented by the JPL ephemeris time argument Teph, in a series of numerically integrated Development Ephemerides. Among them is the DE405 ephemeris in widespread current use. The time scale represented by Teph is closely related to, but distinct from, the TCB time scale currently adopted as a standard by the IAU.
A time standard is a specification for measuring time: either the rate at which time passes or points in time or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time standard can be a time scale, specifying a method for measuring divisions of time. A standard for civil time can specify both time intervals and time-of-day.
In astronomy and celestial navigation, an ephemeris is a book with tables that gives the trajectory of naturally occurring astronomical objects as well as artificial satellites in the sky, i.e., the position over time. The etymology is from Latin ephemeris 'diary' and from Greek ἐφημερίς (ephemeris) 'diary, journal'. Historically, positions were given as printed tables of values, given at regular intervals of date and time. The calculation of these tables was one of the first applications of mechanical computers. Modern ephemerides are often provided in electronic form. However, printed ephemerides are still produced, as they are useful when computational devices are not available.
Barycentric Dynamical Time is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System. TDB is now defined as a linear scaling of Barycentric Coordinate Time (TCB). A feature that distinguishes TDB from TCB is that TDB, when observed from the Earth's surface, has a difference from Terrestrial Time (TT) that is about as small as can be practically arranged with consistent definition: the differences are mainly periodic, and overall will remain at less than 2 milliseconds for several millennia.
Newcomb's Tables of the Sun is a work by the American astronomer and mathematician Simon Newcomb, published in volume VI of the serial publication Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac. The work contains Newcomb's mathematical development of the position of the Earth in the Solar System, which is constructed from classical celestial mechanics as well as centuries of astronomical measurements. The bulk of the work, however, is a collection of tabulated precomputed values that provide the position of the sun at any point in time.
Urania is a large main-belt asteroid that was discovered by English astronomer John Russell Hind on July 22, 1854. It was his last asteroid discovery. This object is named after Urania, the Greek Muse of astronomy. Initial orbital elements for 30 Urania were published by Wilhelm Günther, an assistant at Breslau Observatory. It is orbiting the Sun with a period of 3.64 years and is spinning on its axis once every 13.7 hours.
JPL Horizons On-Line Ephemeris System provides access to key Solar System data and flexible production of highly accurate ephemerides for Solar System objects.
An astronomical constant is any of several physical constants used in astronomy. Formal sets of constants, along with recommended values, have been defined by the International Astronomical Union (IAU) several times: in 1964 and in 1976. In 2009 the IAU adopted a new current set, and recognizing that new observations and techniques continuously provide better values for these constants, they decided to not fix these values, but have the Working Group on Numerical Standards continuously maintain a set of Current Best Estimates. The set of constants is widely reproduced in publications such as the Astronomical Almanac of the United States Naval Observatory and HM Nautical Almanac Office.
Lunar theory attempts to account for the motions of the Moon. There are many small variations in the Moon's motion, and many attempts have been made to account for them. After centuries of being problematic, lunar motion can now be modeled to a very high degree of accuracy.
The Astronomical Almanac is an almanac published by the United States Naval Observatory (USNO) and Her Majesty's Nautical Almanac Office (HMNAO); it also includes data supplied by many scientists from around the world. It is considered a worldwide resource for fundamental astronomical data, often being the first publication to incorporate new International Astronomical Union resolutions. The almanac largely contains Solar System ephemeris and catalogs of selected stellar and extragalactic objects. The material appears in sections, each section addressing a specific astronomical category. The book also includes references to the material, explanations, and examples. It is available one year in advance of its date.
Elena Vladimirovna Pitjeva is a Russian astronomer working at the Institute of Applied Astronomy, Russian Academy of Sciences, St. Petersburg. She has published over 100 articles, as listed in Google Scholar and the Astrophysics Data System in the field of solar system dynamics and celestial mechanics.
Jet Propulsion Laboratory Development Ephemeris designates one of a series of mathematical models of the Solar System produced at the Jet Propulsion Laboratory in Pasadena, California, for use in spacecraft navigation and astronomy. The models consist of numeric representations of positions, velocities and accelerations of major Solar System bodies, tabulated at equally spaced intervals of time, covering a specified span of years. Barycentric rectangular coordinates of the Sun, eight major planets and Pluto, and geocentric coordinates of the Moon are tabulated.
In astronomy, planetary mass is a measure of the mass of a planet-like astronomical object. Within the Solar System, planets are usually measured in the astronomical system of units, where the unit of mass is the solar mass (M☉), the mass of the Sun. In the study of extrasolar planets, the unit of measure is typically the mass of Jupiter (MJ) for large gas giant planets, and the mass of Earth (MEarth) for smaller rocky terrestrial planets.
Éphéméride Lunaire Parisienne is a lunar theory developed by Jean Chapront, Michelle Chapront-Touzé, and others at the Bureau des Longitudes in the 1970s to 1990s.
A fundamental ephemeris of the Solar System is a model of the objects of the system in space, with all of their positions and motions accurately represented. It is intended to be a high-precision primary reference for prediction and observation of those positions and motions, and which provides a basis for further refinement of the model. It is generally not intended to cover the entire life of the Solar System; usually a short-duration time span, perhaps a few centuries, is represented to high accuracy. Some long ephemerides cover several millennia to medium accuracy.
The JPL Small-Body Database (SBDB) is an astronomy database about small Solar System bodies. It is maintained by Jet Propulsion Laboratory (JPL) and NASA and provides data for all known asteroids and several comets, including orbital parameters and diagrams, physical diagrams, close approach details, radar astrometry, discovery circumstances, alternate designations and lists of publications related to the small body. The database is updated daily when new observations are available. In April 2021 the JPL Small-Body Database Browser started using planetary ephemeris (DE441) and small-body perturber SB441-N16. Most objects such as asteroids get a two-body solution (Sun+object) recomputed twice a year. Comets generally have their two-body orbits computed at a time near the perihelion passage as to have the two-body orbit more reasonably accurate for both before and after perihelion. For most asteroids, the epoch used to define an orbit is updated twice a year.
Venus has an orbit with a semi-major axis of 0.723 au, and an eccentricity of 0.007. The low eccentricity and comparatively small size of its orbit give Venus the least range in distance between perihelion and aphelion of the planets: 1.46 million km. The planet orbits the Sun once every 225 days and travels 4.54 au in doing so, giving an average orbital speed of 35 km/s (78,000 mph).
2019 XS is a small Apollo near-Earth asteroid discovered on 2 December 2019 by the Mount Lemmon Survey in Arizona, United States. It passed 1.493 lunar distances from Earth on 9 November 2021 at 03:48 UTC, after which observations were checked by the International Asteroid Warning Network for timing accuracy. During the close pass, the asteroid trailed across the far Southern Hemisphere to the Northern Hemisphere and reached a peak apparent magnitude of 13. Over 1,500 observations of 2019 XS were collected by the Minor Planet Center during the 2021 apparition.
References
- ↑ Standish, E. M., Jr.; Keesey, M. S. W.; and Newhall, X. X. (Feb 1976), JPL Development Ephemeris number 96
- ↑ Newhall, X. X., Standish, E. M., & Williams, J. G (1983), DE 102 – A numerically integrated ephemeris of the moon and planets spanning forty-four centuries Astronomy and Astrophysics (ISSN 0004-6361), vol. 125, no. 1, Aug. 1983, pp. 150–167. (The long ephemeris DE102 has since been superseded by DE406, which is a long (6000-year) version of the current standard DE405.)
- ↑ For example E M Standish (1997) Jet Propulsion Laboratory Planetary and Lunar Ephemerides, (including DE200, DE405 and DE406) published on CD-ROM and other (e.g. online) formats.
- ↑ "(History of USNO Almanac Publications)". Archived from the original on 2009-03-05. Retrieved 2009-02-27.
- ↑ Standish, E. M. & Nobili, A. M. (1997), Galileo's observations of Neptune, Baltic Astronomy, vol. 6, pp. 97–104.
