GEOGRAPHY: CHAPTER - 2: SOLAR SYSTEM

1.    SOLAR SYSTEM: 

• Solar system consists of Planets, moons, asteroids, comets and meteoroids of the objects that travel around it.
• The Solar System formed 4.6 billion years ago from a dense cloud of interstellar gas and dust.
• The size of solar system has been estimated to at about 105 A.U. 
• It takes our solar system about 230 million years to complete one orbit around the galactic center.
• The planets of our solar system and even some asteroids hold more than 150 moons in their orbits.
• The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way.  
• Jupiter, Saturn, Uranus and Neptune are called Terrestrial Planets(Inner planet) & Mercury, Venus, Earth, Mars are called Gaseous Planets(Outer Planet)
• The Solar System also contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter, Beyond Neptune's orbit lie the Kuiper belt and scattered disc, and beyond them a newly discovered population of sednoids.

2.    SUN: 

• The Sun is the Solar System's star and by far its most massive component, its diameter is 14 lakh kms.
• The sun is about 150 million kms. Away from the Earth.
• The Sun is the center of our solar system and makes up 99.8 percent (92.1 percent hydrogen and 7.8 percent helium) held together by its own gravity.
• The Sun's core is about 27 million degrees Fahrenheit (15 million degrees Celsius).
• The Sun is a population I star; it has a higher abundance of elements heavier than hydrogen and helium ("metals" in astronomical parlance) than the older population II stars.
• This high metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets form from the accretion of "metals".

3.    INNER PLANETS: 

• The inner planets are Mercury, Venus, Earth and Mars.
• The four terrestrial or inner planets have dense, Rocky  compositions, few or no moons, and no ring systems.
• Inner Planets are made up of dense metallic minerals & they move faster and have a shorter period of revolution.
• The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth. (I.e. Mercury and Venus).

a)    Mercury: 

• Mercury is the closest planet to the Sun and the smallest planet in the Solar System. 
• Mercury's very tenuous atmosphere consists of atoms blasted off its surface by the solar wind.
• One day on Mercury the time it takes 59 Earth days. One day-night cycle on Mercury takes 175.97 Earth days. Mercury makes a complete orbit around the Sun (a year in Mercury time) in just 88 Earth days.
• Mercury has no moons. There are no rings around Mercury. 

b)    Venus: 

• Venus is the second closest planet to the sun at a distance of about 67 million miles (108 million km).
• One day on Venus lasts 243 Earth days because Venus spins backwards, with its sun rising in the west and setting in the east.
• Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C (752 °F), most likely due to the amount of greenhouse gases in the atmosphere.
• Venus has no moons and no rings.

c)    Earth: 

• Earth is the third planet from the Sun and the fifth largest in the solar system.
• A day on Earth is 24 hours. Earth makes a complete orbit around the sun (a year in Earth time) in about 365 days.
• Earth is a rocky planet with a solid and dynamic surface of mountains, canyons, plains and more. Most of our planet is covered in water.
• Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen, it has one natural satellite.

d)    Mars: 

• Mars (1.5 AU from the Sun) is smaller than Earth and Venus. 
• It has an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars.
• Mars is a rocky planet. Its solid surface has been altered by volcanoes, impacts, winds, crustal movement and chemical reactions.
• Mars has two tiny natural satellites (Deimos and Phobos).

4.    ASTEROID BELT:  

• The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter.
• The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar Systems for mation that failed to coalesce because of the gravitational interference of Jupiter.
• The largest asteroid in the main belt is Ceres, with a diameter of 600 miles.

a)    Ceres: 
       Ceres (2.77 AU) is the largest asteroid, a proto planet, and a dwarf planet. It has a diameter of slightly under 1,000 km, and a mass large enough for its own gravity to pull it into a spherical shape.
b)    Asteroid groups: 
       Asteroids in the asteroid belt are divided into asteroid groups and families based on their orbital characteristics.

5.    OUTER PLANETS: 

• The Outer Planets are far away from the sun (I.e. Jupiter, Saturn, Uranus and Neptune), the outer planets are also called the Jovian planets or gas giants.
• Outer Planets are made up of hot gases, minly hydrogen and helium & they move rather slowly and have a longer period of revolution.

a)    Jupiter: 

• Jupiter is the largest planet of the solar system.
• Jupiter (5.2 AU), at 318 Earth masses, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. 
• Jupiter's strong internal heat creates semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. Jupiter has 79 known satellites. 

b)    Saturn: 

• Saturn is the sixth planet from the sun and the second largest planet in our solar system. 
• Saturn is the only planet of the Solar System that is less dense than water.
• Saturn's atmosphere is made up mostly of hydrogen (H2) and helium (He).
• Saturn is a gas-giant planet and therefore does not have a solid surface like Earth’s. But it might have a solid core somewhere in there.
• Saturn (9.5 AU), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere.  

c)    Uranus: 

• Uranus is the seventh planet from the sun with the third largest diameter in our solar system, Uranus is very cold and windy. 
• Uranus has 27 known satellites, the largest ones being Titania,  Oberon,  Umbriel, Ariel, and Miranda.
• Uranus takes about 17 hours to rotate once (a Uranian day), and about 84 Earth years to complete an orbit of the Sun (a Uranian year).
• Uranus has an atmosphere made mostly of molecular hydrogen and atomic helium, with a small amount of methane.

d)    Neptune: 

• Neptune is the 8th planet of the hydrogen and helium gas giants in our solar system.
• Neptune's atmosphere is made up mostly of molecular hydrogen, atomic helium and methane.
• Neptune (30.1 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and hence more dense. 
• Neptune has 13 moons (and one more awaiting confirmation of discovery), which are named after sea gods and nymphs in Greek mythology.

6.    TRANS-NEPTUNIAN REGION: 

• The orbit of Neptune lies the area of the "trans-Neptunian region", 
• With the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets. 
• The Kuiper Belt should not be confused with the Oort cloud, which is a thousand times more distant.
• The entire region is still largely unexplored.

7.    KUIPER BELT: 

• The Kuiper Belt is a vast rim of primordial debris encircling our solar system.
• It extends between 30 and 50 AU from the Sun.
• There may be hundreds of thousands of icy bodies larger than 100 km (62 miles) and an estimated trillion or more comets within the Kuiper Belt.
• The Kuiper belt can be roughly divided into the "classical" belt and the resonances. Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two).

8.    PLUTO AND CHARON: 

• Pluto’s five moons and approximately the size of Texas is almost half the size of Pluto itself.
• Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion.
• Charon neither rises nor sets, but hovers over the same spot on Pluto's surface, and the same side of Charon always faces Pluto a phenomenon called mutual tidal locking.
• Pluto has a 3:2 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits.

9.    METEORS & METEORITES: 

• A small body moving in the solar system that would become a meteor if it entered the earth's atmospherae. Little chunks of rock and debris in space are called meteoroids.
• Meteoroids have a pretty big size range. They include any space debris bigger than a molecule and smaller than about 330 feet.
• One of the most intact impact craters is the Barringer Meteorite Crater in Arizona, about 1 kilometer (0.6 mile) across, formed by the impact of a piece of iron-nickel metal approximately 50 meters (164 feet) in diameter.

10.     COMETS: 

• Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun.
• As theorized by astronomer Gerard Kuiper in 1951, a disc-like belt of icy bodies exists beyond Neptune, where a population of dark comets orbits the Sun in the realm of Pluto.
• Each comet has a tiny frozen part, called a nucleus, often no larger than a few kilometers across.
• Most comets travel a safe distance from the Sun.
• Comet Halley comes no closer than 89 million kilometers (55 million miles).

11.     STARS:  

• A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. 
• The nearest star to Earth is the Sun. 
• A solar system is a star and all of the objects that travel around it—planets, moons, asteroids, comets and meteoroids. 
• Most stars host their own planets, so there are likely tens of billions of other solar systems in the Milky Way galaxy alone. 
• Astronomers have determined that these stars are orbiting a massive black hole that lies at the very center of the galaxy.
• A star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space.
• A star with mass greater than 0.4 times the Sun's will expand to become a red giant when the hydrogen fuel in its core is exhausted.

12.     CONSTELLATIONS: 

• A constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices.
• In 1928, the International Astronomical Union (IAU) ratified and recognized 88 modern constellations, with contiguous boundaries defined by right ascension and declination. 
• The Pleiades and Hyades within the constellation Taurus and the Cross split between the southern constellations Carina and Vela.

13.     GALAXY: 

• A Galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.
• Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular.
• The majority of galaxies are gravitationally organized into groups, clusters, and super clusters. 
• The largest structure of galaxies yet recognized is a cluster of super clusters that has been named Laniakea, which contains the Virgo super cluster.

14.    NEBULAE: 

• A Nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases.
• Nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way.
• Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula
• The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.