ASTRONOMYSUNPLANETSANDGALAXY

WHATISASTRONOMY?Astronomy is a natural science which is the study of celestial objects such as stars, galaxies, planets, moons, asteroids, comets and nebulae. It also deals with physics, chemistry, and phenomena that originate outside the atmosphere of Earth, including supernovae explosions, gamma ray bursts, and cosmic microwave background radiation.

PHYSICALCOSMOLOGYA related but distinct subject, physical cosmology, is concerned with studying the universe as a whole.

HISTORYAstronomy is one of the oldest sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, and Maya performed methodical observations of the night sky.

THESOLARSYSTEMThe Solar System comprises the Sun and the objects that orbit it. Of those objects that orbit the Sun directly, the largest eight are the planets that form the planetary system around it, while the remainder are smaller objects, such as dwarf planets and small Solar System bodies such as comets and asteroids.

STARSPLANETSSATELLITESCOMETSStars: 1 Sun Planets: 8 – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, NeptuneKnown dwarf planets: Possibly several hundred; five currently recognized: Ceres, Pluto, Haumea, Makemake, ErisKnown natural satellites: 450 (173 planetary and 277 minor planetary)Known minor planets: 688,621Known comets: 3,354Identified rounded satellites: 19

THESUNThe Sun is the star at the center of the Solar System and is by far the most important source of energy for life on Earth. It is a nearly perfect spherical ball of hot plasma.Its diameter is about 109 times that of Earth, and it has a mass about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System.

MERCURYMercury is the smallest and closest to the Sun of the eight planets in the Solar System, with an orbital period of about 88 Earth days. It has no known natural satellites.The planet is named after the Roman messenger to the gods.

Composite of the north pole of Mercury, where NASA confirmed the discovery of a large volume of water ice, in permanently dark craters that exist there

VENUSVenus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has no natural satellite. It is named after the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky.Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar: Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass). Their densities and chemical compositions are similar.

EARTHEarth, also called the world and, less frequently, Gaia or, in Latin, Terra, is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to accommodate life.

MARSMars is the fourth planet from the Sun and the second smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is often referred to as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance.Mars is a terrestrial planet with a thin atmosphere, having the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth.

JUPITERJupiter is the fifth planet from the Sun and the largest planet in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, but is two and a half times that of all the other planets in the Solar System combined. Jupiter is a gas giant, along with Saturn (Uranus and Neptune are ice giants). Jupiter was known to astronomers of ancient times. The Romans named it after their god Jupiter.

SATURNSaturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant with an average radius about nine times that of Earth. Although only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive. Saturn is named after the Roman god of agriculture, its astronomical symbol represents the god's sickle.

URANUSUranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants.It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of −224 °C. The interior of Uranus is mainly composed of ices and rock.

NEPTUNENeptune is the eighth and farthest planet from the Sun in the Solar System. It is the fourth-largest planet by diameter and the third-largest by mass. Among the giant planets in the Solar System, Neptune is the most dense. Neptune is 17 times the mass of Earth.Named after the Roman god of the sea, its astronomical symbol is , a ♆stylised version of the god Neptune's trident.

PLUTOPluto was discovered in 1930 by Clyde Tombaugh, and was originally considered the ninth planet from the Sun. After 1992, its status as a planet fell into question following the discovery of several objects of similar size in the Kuiper belt.It is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun.

THEMILKYWAYThe Milky Way is the galaxy that contains our Solar System.Its name "milky" is derived from its appearance. The term "Milky Way" is a translation of the Latin via lactea.The Milky Way is estimated to contain 100–400 billion stars, although this number may be as high as one trillion.There are probably at least 100 billion planets in the Milky Way.The Solar System is located within the disk, about 27,000 light-years from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm.