SUMMARY / RELATED TOPICS

Ecliptic

The ecliptic is the mean plane of the apparent path in the Earth's sky that the Sun follows over the course of one year. This plane of reference is coplanar with Earth's orbit around the Sun; the ecliptic is not noticeable from Earth's surface because the planet's rotation carries the observer through the daily cycles of sunrise and sunset, which obscure the Sun's apparent motion against the background of stars during the year. The motions as described above are simplifications; because of the movement of Earth around the Earth–Moon center of mass, the apparent path of the Sun wobbles with a period of about one month. Because of further perturbations by the other planets of the Solar System, the Earth–Moon barycenter wobbles around a mean position in a complex fashion; the ecliptic is the apparent path of the Sun throughout the course of a year. Because Earth takes one year to orbit the Sun, the apparent position of the Sun takes one year to make a complete circuit of the ecliptic. With more than 365 days in one year, the Sun moves a little less than 1° eastward every day.

This small difference in the Sun's position against the stars causes any particular spot on Earth's surface to catch up with the Sun about four minutes each day than it would if Earth would not orbit. Again, this is a simplification, based on a hypothetical Earth that orbits at uniform speed around the Sun; the actual speed with which Earth orbits the Sun varies during the year, so the speed with which the Sun seems to move along the ecliptic varies. For example, the Sun is north of the celestial equator for about 185 days of each year, south of it for about 180 days; the variation of orbital speed accounts for part of the equation of time. Because Earth's rotational axis is not perpendicular to its orbital plane, Earth's equatorial plane is not coplanar with the ecliptic plane, but is inclined to it by an angle of about 23.4°, known as the obliquity of the ecliptic. If the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes.

The Sun, in its apparent motion along the ecliptic, crosses the celestial equator at these points, one from south to north, the other from north to south. The crossing from south to north is known as the vernal equinox known as the first point of Aries and the ascending node of the ecliptic on the celestial equator; the crossing from north to south is descending node. The orientation of Earth's axis and equator are not fixed in space, but rotate about the poles of the ecliptic with a period of about 26,000 years, a process known as lunisolar precession, as it is due to the gravitational effect of the Moon and Sun on Earth's equatorial bulge; the ecliptic itself is not fixed. The gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of Earth's orbit, hence of the ecliptic, known as planetary precession; the combined action of these two motions is called general precession, changes the position of the equinoxes by about 50 arc seconds per year.

Once again, this is a simplification. Periodic motions of the Moon and apparent periodic motions of the Sun cause short-term small-amplitude periodic oscillations of Earth's axis, hence the celestial equator, known as nutation; this adds a periodic component to the position of the equinoxes. Obliquity of the ecliptic is the term used by astronomers for the inclination of Earth's equator with respect to the ecliptic, or of Earth's rotation axis to a perpendicular to the ecliptic, it is about 23.4° and is decreasing 0.013 degrees per hundred years because of planetary perturbations. The angular value of the obliquity is found by observation of the motions of Earth and other planets over many years. Astronomers produce new fundamental ephemerides as the accuracy of observation improves and as the understanding of the dynamics increases, from these ephemerides various astronomical values, including the obliquity, are derived; until 1983 the obliquity for any date was calculated from work of Newcomb, who analyzed positions of the planets until about 1895: ε = 23° 27′ 08″.26 − 46″.845 T − 0″.0059 T2 + 0″.00181 T3 where ε is the obliquity and T is tropical centuries from B1900.0 to the date in question.

From 1984, the Jet Propulsion Laboratory's DE series of computer-generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated: ε = 23° 26′ 21″.45 − 46″.815 T − 0″.0006 T2 + 0″.00181 T3 where hereafter T is Julian centuries from J2000.0. JPL's fundamental ephemerides have been continually updated; the Astronomical Almanac for 2010 specifies:ε = 23° 26′ 21″.406 − 46″.836769 T − 0″.0001831 T2 + 0″.00200340 T3 − 0″.576×10−6 T4 − 4″.34×10−8 T5 These expressions for the obliquity are intended for high precision over a short time span ± several centuries. J. Laskar computed an expression to order T10 good to 0″.04/1000 years over 10,000 years. All of these expressions are for the mean obliquity, that is, without the nutation of the equator included; the true or instantaneous obliquity includes the nutation. Most of the major bodies of the So

PĂ©ligre Dam

The Péligre Dam is a gravity dam located off the Centre department on the Artibonite River of Haiti. At 72 m it is the tallest dam in Haiti; the dam was created as a flood-control and an energy-providing measure in the Artibonite River Valley during the 1950s as part of the Artibonite Valley Agricultural Project. This dam impounds Lake Péligre. Despite its purpose of providing energy throughout Haiti, many contend that the energy provided by the dam is not distributed equitably. Furthermore, the dam has had significant environmental and health consequences on the local people who were forced to relocate as a result of the dam's completion; these are points of concern to academics and human rights activists who, noting heavy North American involvement in the planning and construction of the dam, believe that neoliberal influences may be at play. The Péligre dam is in the largest hydrographic basin in Haiti; the power plant contains three 17 MW Francis turbine-generators for an installed capacity of 51 MW.

The Péligre Dam was proposed as a means to rehabilitate the agricultural lands of the Central Plateau through control of floods as well as to generate hydroelectricity to fuel the industrial expansion of Haiti. The dam was built on the Artibonite River; this river was the first source of hydroelectric irrigation water in Haiti. The dam was popularized throughout the country as a mechanism for increased crop yields via controlled irrigation. Rice grown for export, in particular, was the target of this irrigation intervention. In addition, it was believed that the generation of a reliable supply of electricity from the dam would drive economic growth and reduce social disparity. Planning and construction of the dam was influenced by the United States of America; the dam was nicknamed the “Little TVA” after the Tennessee Valley Authority, because of its purpose of providing energy for all of Haiti. The dam was designed by the United States Army Corps of Engineers, it was funded by the Export Import Bank of the United States.

Construction on the dam was overseen by engineer André A. Loiselle; the dam was completed in 1956 by the US Army Corps of Engineers and Brown & Root thus creating Lake Péligre in the process. The Péligre Hydroelectric Plant, the power plant associated with the dam, went online in 1971, 15 years after the completion of the dam itself, it is operated by the Electricite d’Haiti, or Electricity of Haiti, which reports to the Ministry of Public Works and Communications in Haiti. The main purpose of Electricite d’Haiti is electricity generation. Under the management of Electricite d’Haiti, the Péligre Hydroelectric Plant supplies 30% of the country's electricity. Despite the plant's purpose to provide reliable energy to all of Haiti, there are some questions as to whether or not the dam achieves that goal in reality. Lumas Kendrick, of the Inter-American Development Bank states that, of the energy, generated by the dam, over half is lost due to poor power lines, defective transformers, billing issues.

Of the energy, generated and distributed, it is limited in its ability to reach all of Haiti, as only 12 per cent of the country has electrical wires. These areas with electricity are concentrated around urban centers, thereby reducing the overall impact of the hydroelectric power on rural development in the country. Silting has reduced the operational capacity of the dam for the generation of electricity; the upper Artibonite watershed is faced with issues of severe erosion, caused by deforestation and agriculture. The erosion is estimated at 1,305 metric tons per km2 per year on average; the problems of heavy deforestation and soil erosion in rainy seasons have caused a large amount of sediment to become trapped in the dam, reducing its functionality. Additionally, the silt in the Péligre reservoir has decreased the reservoir storage capacity from 600 million cubic metres to 300 MCM in 60 years. Reforestation and erosion control methods discussed before the dam's creation have not been carried out.

As a result of the dam's reduced functioning, Haiti's electricity generation fell by more than 30 per cent from 2004-2010. The dam and power plant were damaged during the 2010 Haiti earthquake. With the functional lifespan of the dam coming to a close, the Inter-American Development Bank and several other international organizations decided to fund a three-year, forty-eight million dollar rehabilitation for the dam, to be undertaken by Alstom and Compagnie de Montages Electriques a l’Exportation; this project is intended by the Inter-American Development Bank to increase the lifespan of the dam and power station by another twenty years. Despite being called a technical success by donor agencies and NGOs, the Péligre Dam is considered in many local and humanitarian circles to be a failure, due the destruction of local communities and the displacements of residents. In terms of power distribution, it has been asserted that the electricity from the dam is distributed to agribusinesses, foreign-owned factories, homes of the wealthier class in Port-au-Prince.

Additionally, the continued energy starvation of rural residences is considered to contribute to the low development indicators in rural parts of the country, linked to lack of access to clean water and energy poverty and insecurity. The dam is set in the Péligre basin of the Central Plateau in Haiti; this area is home to several hundred thousand rural people. As a result of the completion of the dam in 1956, thousands of families were forced to flee their fertile land in the Artibonite Valley due to flooding caused by the Péligre Dam; these families, all of which were poor, rural peasant farmers, were forced to move to seek employmen

GU Piscium b

GU Piscium b is a directly imaged planetary-mass companion orbiting the star GU Piscium, with an large orbit of 2,000 AU, an apparent angular separation of 42 arc seconds. The planet is located at right ascension 01h 12m 36.48s declination +17° 04′ 31.8″ at a distance of 48 pc. An orbital revolution around its parent star or "year", would take 163,000 years to complete, considering a circular orbit with 2000 AU as the semi-major axis, it is a gas giant located in the constellation of Pisces, 155 light-years from the Solar System, estimated to have a mass nine to thirteen times that of Jupiter, a surface temperature of 1000 K. It is a young stellar system, part of the AB Doradus moving group of ca. 30 main stars created from the same molecular cloud less than 100 million years ago, the only one found among the 90 stars of the group examined. The discovery was made by an international team of astronomers led by Marie-Eve Naud of the Université de Montréal in Quebec, combining observations from telescopes of the Gemini Observatory, the Mont Mégantic Observatory, the Canada–France–Hawaii Telescope and the W. M. Keck Observatory.

Its large distance away from its parent star permitted the use of combined infra-red and visible light images to detect it, a technique astronomers hope to reproduce to discover much closer planets with the Gemini Planet Imager in Chile. Near-infrared spectroscopy of the companion was obtained with the GNIRS spectrograph on the Gemini North Telescope, which shows evidence of low surface gravity confirming the planet's youth. Weak methane absorption was detected in H and K band corresponding to a spectral type of T3.5. List of exoplanet extremes List of directly imaged exoplanets CFBDSIR 2149−0403 - Possible rogue planet in the AB Doradus moving group WD 0806−661 Y-type sub-brown dwarf, it is the planetary-mass object with the widest known separation from its host star and it has the widest angular separation as seen from Earth. IOPscience: DISCOVERY OF A WIDE PLANETARY-MASS COMPANION TO THE YOUNG M3 STAR GU PSC arXiv: Discovery of a wide planetary-mass companion to the young M3 star GU Psc NASA ADS: Discovery of a Wide Planetary-mass Companion to the Young M3 Star GU Psc