ASTRO

• Sun


  A star that is brighter than about 80% of the stars in the Galaxy, by far the most massive member of the solar system. An enormous ball about 1.4 million kilometers in diameter, with surface layers of incandescent gas and an interior temperature of millions of degrees.
• We have also been discovering smaller worlds beyond Neptune that are called trans-Neptunian objects or TNOs
• The first to be found, in 1930, was Pluto, but others have been discovered during the twenty-first century
• The four planets closest to the Sun

  • Mercury
  • Venus
  • Earth
  • Mars
• Terrestrial planets


  Relatively small worlds, composed primarily of rock and metal, with solid surfaces that bear the records of their geological history in the forms of craters, mountains, and volcanoes
• The next four planets

  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• Jovian planets


  Much larger and composed primarily of lighter ices, liquids, and gases
• The asteroids, rocky bodies that orbit the Sun like miniature planets, mostly in the space between Mars and Jupiter. Most asteroids are remnants of the initial population of the solar system that existed before the planets themselves formed
• Comets


  Objects composed mostly of ice, made of frozen gases such as water, carbon dioxide, and carbon monoxide. Remnants from the formation of the solar system, formed and continue to orbit the Sun in distant, cooler regions
• Countless grains of broken rock, which we call cosmic dust, scattered throughout the solar system. When these particles enter Earth's atmosphere (as millions do each day) they burn up, producing a brief flash of light in the night sky known as a meteor (meteors are often referred to as shooting stars)
• Meteorite


  A larger chunk of rocky or metallic material that survives its passage through the atmosphere and lands on Earth
• Three largest moons


  • Ganymede
  • Callisto
  • Titan
• The orbits of the planets are prograde (i.e. if seen from above the North pole of the Sun they all revolve in a counter-clockwise direction)
• The Nebular Theory of the origin of the Solar System

  Solar system formed about 4.6 billion year ago, when gravity pulled together low-density cloud of interstellar gas and dust called nebula. The Orion Nebula, an interstellar cloud in which star systems and possibly planets are forming. Initially the cloud was about several light years across.
• The asteroid belt -- located between Mars and Jupiter -- is made of thousands of rocky planetesimals from 1,000 km to a few meters across
• The Sun


  The star at the center of the Solar System. A nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. It is the largest object in the solar system, with a diameter of about 1.39 million kilometers, or 109 times that of Earth, and a mass about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. The Sun is classified as a yellow dwarf star.
• The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol
• Layers of the Sun

  • Core
  • Radiative zone
  • Tachocline
  • Convective zone
  • Photosphere
• Layers of the atmosphere of the Sun

  • Chromosphere
  • Solar transition region
  • Corona
  • Heliosphere
• The Sun rotates more quickly at its equator than it does close to its poles. This is known as differential rotation
• Moons


  Also called natural satellites, they are generally solid bodies, and few have atmospheres
• The Moon


  The only natural satellite of Earth. It was created 4.6 billion years ago, and it is widely accepted that it was created when Earth collided with a planet-sized object called Theia
• Comets


  Sometimes called dirty snowballs or "icy mudballs". They are a mixture of ices (both water and frozen gases) and dust that for some reason didn't get incorporated into planets when the solar system was formed. Comets are invisible except when they are near the Sun.
• Parts of the comet when it is active and near the Sun

  • Nucleus
  • Coma
  • Hydrogen cloud
  • Dust tail
  • Ion tail
• In the first day of January 1801, Giuseppe Piazzi discovered an object which he first thought was a new comet. But after its orbit was better determined it was clear that it was not a comet but more like a small planet. Piazzi named it Ceres, after the Sicilian goddess of grain.
• Classification of asteroids (spectra and albedo)

  • C-types (chondrites)
  • S-types (siliceous)
  • M-types (metallic)
• Asteroid categories by position in the solar system

  • Main Belt
  • Near-Earth Asteroids (NEAs)
  • Atens
  • Apollos
  • Amors
  • Trojans
• Between the main concentrations of asteroids in the Main Belt are relatively empty regions known as the Kirkwood gaps
• Some of the larger asteroids can also be referred to as planetoids and minor planets. Ceres is the only dwarf planet to still keep its asteroid label
• The asteroid belt was first discovered in 1801. This is when Giuseppe Piazzi discovered Ceres. Ceres is a dwarf planet and was the first object to be observed in the asteroid belt
• The asteroid belt is a disc shape, located between the orbits of Mars and Jupiter
• Ceres is the only dwarf planet in the asteroid belt. The four largest objects in the belt are Ceres, Vesta, Pallas and Hygiea
• Meteoroid


  A solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom
• Meteor shower


  A series of many meteors appearing seconds or minutes apart and appearing to originate from the same fixed point in the sky
• Meteor


  The visible passage of a glowing meteoroid, micrometeoroid, comet or asteroid through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere creating a streak of light via its rapid motion and sometimes also by shedding glowing material in its wake
• Meteorite


  A portion of a meteoroid or asteroid that survives its passage through the atmosphere and hits the ground without being destroyed
• The five dwarf planets

  • Pluto
  • Ceres
  • Haumea
  • Makemake
  • Eris
• Pluto


  The largest known dwarf planet in the Solar System, thought to be the 9th planet of our system for 75 years until the discovery of Eris and other similar objects that led to its demotion from a planet to a dwarf planet in 2006
• Moons of Pluto

  • Charon
  • Nix
  • Styx
  • Kerberos
  • Hydra
• Ceres


  A dwarf planet, and the only one who isn't located in the Kuiper Belt but rather in the inner solar system in the asteroid belt between the orbits of Mars and Jupiter