The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury; the Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter; the four smaller inner planets, Venus and Mars, are terrestrial planets, being composed of rock and metal. The four outer planets are giant planets, being more massive than the terrestrials; the two largest and Saturn, are gas giants, being composed of hydrogen and helium. All eight planets have circular orbits that lie within a nearly flat disc called the ecliptic.
The Solar System contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed of ices, beyond them a newly discovered population of sednoids. Within these populations are several dozen to tens of thousands of objects large enough that they have been rounded by their own gravity; such objects are categorized as dwarf planets. Identified dwarf planets include the trans-Neptunian objects Pluto and Eris. In addition to these two regions, various other small-body populations, including comets and interplanetary dust clouds travel between regions. Six of the planets, at least four of the dwarf planets, many of the smaller bodies are orbited by natural satellites termed "moons" after the Moon; each of the outer planets is encircled by planetary rings of dust and other small objects.
The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; the Oort cloud, thought to be the source for long-period comets, may exist at a distance a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy. For most of history, humanity did not understand the concept of the Solar System. Most people up to the Late Middle Ages–Renaissance believed Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system.
In the 17th century, Galileo discovered that the Sun was marked with sunspots, that Jupiter had four satellites in orbit around it. Christiaan Huygens followed on from Galileo's discoveries by discovering Saturn's moon Titan and the shape of the rings of Saturn. Edmond Halley realised in 1705 that repeated sightings of a comet were recording the same object, returning once every 75–76 years; this was the first evidence that anything other than the planets orbited the Sun. Around this time, the term "Solar System" first appeared in English. In 1838, Friedrich Bessel measured a stellar parallax, an apparent shift in the position of a star created by Earth's motion around the Sun, providing the first direct, experimental proof of heliocentrism. Improvements in observational astronomy and the use of unmanned spacecraft have since enabled the detailed investigation of other bodies orbiting the Sun; the principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally.
The Sun's four largest orbiting bodies, the giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. The remaining objects of the Solar System together comprise less than 0.002% of the Solar System's total mass. Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic; the planets are close to the ecliptic, whereas comets and Kuiper belt objects are at greater angles to it. All the planets, most other objects, orbit the Sun in the same direction that the Sun is rotating. There are exceptions, such as Halley's Comet; the overall structure of the charted regions of the Solar System consists of the Sun, four small inner planets surrounded by a belt of rocky asteroids, four giant planets surrounded by the Kuiper belt of icy objects. Astronomers sometimes informally divide this structure into separate regions; the inner Solar System includes the asteroid belt. The outer Solar System is including the four giant planets.
Since the discovery of the Kuiper belt, the outermost parts of the Solar Sys
NGC 1073 is a barred spiral galaxy in the constellation Cetus. It has an H II nucleus. NGC 1073 is about 55 million light years from Earth. NGC 1073 is about 80,000 light years across. NGC 1073 can be viewed with a mid-sized telescope and is found in the Cetus constellation called the Sea Monster. NGC 1073 is a barred spiral galaxy like the Milky Way. NGC 1073 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images Video
NGC 3953 is a barred spiral galaxy located in the constellation Ursa Major. The galaxy is known to exhibit an inner ring structure that encircles the bar.. Two supernovae have been identified within NGC 3953: the type Ia supernova SN 2001dp and SN 2006bp. NGC 3953 is a member of the M109 Group, a large group of galaxies located within the constellation Ursa Major that may contain over 50 galaxies. Spiral Galaxy NGC 3953 - Supernova 2001 dp SEDS: Spiral Galaxy NGC 3953
NGC 4921 is a barred spiral galaxy in the Coma Cluster, located in the constellation Coma Berenices. It is about 320 million light-years from Earth; the galaxy has a nucleus with a bar structure, surrounded by a distinct ring of dust that contains formed, hot blue stars. The outer part consists of unusually smooth, poorly distinguished spiral arms. In 1976, Canadian astronomer Sidney Van den Bergh categorized this galaxy as "anemic" because of the low rate at which stars are being formed, he noted that it has "an unusually low surface brightness and exhibits remarkably diffuse spiral arms". Nonetheless, it is the brightest spiral galaxy in the Coma Cluster; this galaxy is located near the center of the cluster and has a high relative velocity compared to the mean cluster velocity. When examined at the 21 cm wavelength Hydrogen line, NGC 4921 was found to be H I deficient, indicating it is low in hydrogen; the distribution of hydrogen has been perturbed toward the SE spiral arm and is less extended than the optical disk of the galaxy.
This may have been caused by interaction with the intergalactic medium, stripping off the gas. On May 4, 1959, a supernova explosion was observed in this galaxy by M. L. Humason using a Schmidt telescope at the Palomar Observatory, it appeared "quite far from the center" of the galaxy, reached an estimated peak magnitude of 18.5. The light curve proved similar to supernova SN 1987a in the Large Magellanic Cloud, it displayed "unusual photometric behavior"
Messier 95 known as M95 or NGC 3351, is a barred spiral galaxy located about 33 million light-years away in the zodiac constellation Leo. It was discovered by Pierre Méchain in 1781, catalogued by fellow French astronomer Charles Messier four days later. On 16 March 2012, a supernova was discovered in M95; the galaxy has a morphological classification of SBb, with the SBb notation indicating it is a barred spiral with arms that are intermediate on the scale from to loosely wound, an" meaning an inner ring surrounds the bar. The latter is a ring-shaped, circumnuclear star-forming region with a diameter of 2,000 light-years; the spiral structure extends outward from the ring. The ring structure of M95 has a mass of 3.5×108 M☉ in molecular gas and a star formation rate of 0.38 M☉ yr−1. The star formation is occurring in at least five regions with diameters between 100 and 150 pc that are composed of several star clusters ranging in size from 1.7 to 4.9 pc. These individual clusters contain ×106 M☉ of stars, may be on the path to forming globular clusters.
A Type II supernova, designated as SN 2012aw, was discovered in M95 on 16 March 2012. The light curve of the supernova displayed a significant flattening after 27 days, thus classifying it as a Type II-P, or "plateau", core-collapse supernova; the disappearance of the progenitor star was confirmed from near-infrared imaging of the region. The brightness of the presumed red supergiant progenitor allowed its mass to be estimated as 12.5±1.5 M☉. M95 is one of several galaxies within a group of galaxies in the constellation Leo; the group includes the Messier objects M96 and M105. Messier 95 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images SEDS: Spiral Galaxy M95 NASA Astronomy Picture of the Day: Barred Spiral Galaxy M95 Merrifield, Michael. "Supernova in M95 – SN 2012aw and its progenitor". Deep Space Videos. Brady Haran
Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, its symbol is ♍. Lying between Leo to the west and Libra to the east, it is the second-largest constellation in the sky and the largest constellation in the zodiac, it can be found through its brightest star, Spica. The bright star Spica makes it easy to locate Virgo, as it can be found by following the curve of the Big Dipper/Plough to Arcturus in Boötes and continuing from there in the same curve. Due to the effects of precession, the First Point of Libra, lies within the boundaries of Virgo close to β Virginis; this is one of the two points in the sky where the celestial equator crosses the ecliptic This point will pass into the neighbouring constellation of Leo around the year 2440. Besides Spica, other bright stars in Virgo include β Virginis, γ Virginis, δ Virginis and ε Virginis. Other fainter stars that were given names are ζ Virginis, η Virginis, ι Virginis, κ Virginis, λ Virginis and φ Virginis; the star 70 Virginis has one of the first known extrasolar planetary systems with one confirmed planet 7.5 times the mass of Jupiter.
The star Chi Virginis has one of the most massive planets detected, at a mass of 11.1 times that of Jupiter. The sun-like star 61 Virginis has three planets: one is a super-Earth and two are Neptune-mass planets. SS Virginis is a variable star with a noticeable red color, it varies in magnitude from a minimum of 9.6 to a maximum of 6.0 over a period of one year. There are 35 verified exoplanets orbiting 29 stars in Virgo, including PSR B1257+12, 70 Virginis, Chi Virginis, 61 Virginis, NY Virginis, 59 Virginis; because of the presence of a galaxy cluster within its borders 5° to 12° west of ε Vir, this constellation is rich in galaxies. Some examples are Messier 49, Messier 58, Messier 59, Messier 60, Messier 61, Messier 84, Messier 86, Messier 87, Messier 89 and Messier 90. A noted galaxy, not part of the cluster is the Sombrero Galaxy, an unusual spiral galaxy, it is located about 10° due west of Spica. NGC 4639 is a face-on barred spiral galaxy located 78 Mly from Earth, its outer arms have a high number of Cepheid variables, which are used as standard candles to determine astronomical distances.
Because of this, astronomers used several Cepheid variables in NGC 4639 to calibrate type 1a supernovae as standard candles for more distant galaxies. Virgo possesses several galaxy clusters, one of, HCG 62. A Hickson Compact Group, HCG 62 is at a distance of 200 Mly from Earth and possesses a large central elliptical galaxy, it has a heterogeneous halo of hot gas, posited to be due to the active galactic nucleus at the core of the central elliptical galaxy. M87 is the largest galaxy in the Virgo cluster, is at a distance of 60 Mly from Earth, it is a major radio source due to its jet of electrons being flung out of the galaxy by its central supermassive black hole. Because this jet is visible in several different wavelengths, it is of interest to astronomers who wish to observe black holes in a unique galaxy. M84 is another elliptical radio galaxy in the constellation of Virgo. Astronomers have surmised that the speed of the gas clouds orbiting the core indicates the presence of an object with a mass 300 million times that of the sun, most a black hole.
The Sombrero Galaxy, M104, is an edge-on spiral galaxy located 28 million light-years from Earth. It has a bulge at its center made up of older stars, larger than normal, it is surrounded by large, bright globular clusters and has a prominent dust lane made up of polycyclic aromatic hydrocarbons. NGC 4438 is a peculiar galaxy with an active galactic nucleus, at a distance of 50 Mly from Earth, its supermassive black hole is ejecting jets of matter, creating bubbles with a diameter of up to 78 ly. NGC 4261 has a black hole 20 ly from its center with a mass of 1.2 billion solar masses. It is located at a distance of 45 Mly from Earth, has an unusually dusty disk with a diameter of 300 ly. Along with M84 and M87, NGC 4261 has strong emissions in the radio spectrum. IC 1101 is a supergiant elliptical galaxy in the Abell 2029 galaxy cluster located about 1.07 Gly from Earth. At the diameter of 5.5 million light years, or more than 50 times the size of the Milky Way, it was the largest known galaxy in the universe.
Virgo is home to the quasar 3C 273, the first quasar to be identified. With a magnitude of ~12.9 it is the optically brightest quasar in the sky. In the Babylonian MUL. APIN, part of this constellation was known as "The Furrow", representing the goddess Shala and her ear of grain. One star in this constellation, retains this tradition as it is Latin for "ear of grain", one of the major products of the Mesopotamian furrow. For this reason the constellation became associated with fertility; the constellation of Virgo in Hipparchus corresponds to two Babylonian constellations: the "Furrow" in the eastern sector of Virgo and the "Frond of Erua" in the western sector. The Frond of Erua was depicted as a godde