Galaxies and stars

• A massive gravitationally bound system consisting of stars stellar remnants and interstellar medium of gas and dust and dark matter


  Galaxy
• Contains varying numbers of planets, star systems, star clusters and types of interstellar stars

  Galaxy
• Galaxy derived from the Greek word 


  Galaxias meaning milky cone or kylkos ("circle") galaktikos ("milky")
• Types of galaxies


  Elliptical, Spiral, Barred - Spiral Galaxy, Irregular Galaxy
• Shaped like spheroid or elongated sphere

  Elliptical Galaxy
• Have no particular axis rotation

  Elliptical Galaxy
• Have three main components

  Spiral Galaxy
• The three main components of spiral Galaxy

  Bulge, disk, halo
• Spherical structure found in the center of the galaxy

  Bulge
• Made up of gas, dust, and younger stars

  DISK
• loose, spherical structure located around the bulge and some of the disk

  Halo
• Bulge ontains old clusters of stars, know as ________ _______

  globular clusters
• Spiral Galaxy with a central bar - shaped structure composed of stars


  Barred - Spiral Galaxy
• Have no regular or symmetrical structure neither spiral or elliptical

  Irregular Galaxy
• Among the smallest galaxies and contain a vast amount of gas and dust

  Irregular Galaxy
• Examples of galaxy


  Andromeda, Milky Way, Dwarf Spheroidal Galaxy, Large Magellanic Clouds,
• A spiral galaxy approximately 2.5 million light years from earth


  Andromeda Galaxy
• Similar to milky way size and shape with about 100 billion stars gas and dust turning in spiral pinwheel

  Andromeda Galaxy
• Is a barred spiral galaxy with a flat rotating disc consisting of gas dust and stars estimated 100,000 to 120,000 light years across

  Milky Way
• Nearest galactic neighbor for about 80,000 light years from the solar system diameter of only 1,000 light years

  Dwarf Spheroidal Galaxy
• Irregular galaxy which is also a neighboring galaxy of milky way duo of irregular dwarf galaxies


  Large Magellanic Clouds
• Massive luminous sphere of plasma held together by its own gravity

  Stars
• Most widely recognized astronomical objects and represent the most fundamental building blocks of galaxies

  Stars
• Stars are born from swirling clouds of hydrogen gas in deep space between stars


  Nebulae
• Radiating band and accumulation of cloud of gas formed due to condensation of mutual gravitational attraction which further lead to the birth of a star

  Protostar
• Brightness of stars is measured from

  Amount of light produced, size of the star, distance to a particular star
• Measures the brightness of stars which is based on a system established

  Apparent magnitude scale
• Who is established the system of apparent magnitude scale

  Hipparchus
• Star types

  Main sequence star, Red giants, white dwarfs, variable stars, alpha centuari, proxima centuari, Rigel, Canopus, Sirius, Betelgeuse, Antares, Aldebaran, Procyon, Sun
• Normal, mature stars


  Main sequence stars
• Bright full but low temperature reddish stars

  Red giants
• Can be hundred times larger than the sun but have the same mass of that of the sun

  Red giants
• Faint white hot stars

  White dwarfs
• Change the brightness over time

  Variable Stars
• Is a bright variable star that is used to measure distances

  Cepheid variable
• Brightest star in the southern constellation of centaurus and the third brightest star in the night sky

  Alpha centuari
• A red dwarf star which is approximately 424 light years distance from the sun making it the closest and the nearest star from the sun

  Proxima centuari
• Too faint to see in the naked eye with the apparent magnitude of 11.05

  Proxima centuari
• Brightest star in the constellation orion and the seven brightest star in the night sky with visual magnitude 0.13

  Rigel
• A blue - white supergiant which is a triple star system with an absolute magnitude -7.84 and around 120,000 times as luminous is the sun

  Rigel