Variable Star, Types of Variable Stars, Supernova, Observations of Variable Stars (For CBSE, ICSE, IAS, NET, NRA 2022)

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Variable Star

  • Variable star, any star whose observed light varies notably in intensity
  • Astronomy is a science that allows amateurs to contribute to front-line professional research.
  • The changes in brightness may be periodic, semiregular, or completely irregular.
  • For more than a century, amateurs have collected the brightness data record of variable stars of several significant types using simple backyard telescopes.

About Variable Stars

  • They are stars that change brightness.
  • The change can vary from – thousandth of a magnitude to as much as twenty magnitudes over periods of a fraction of a second to years.
  • Almost 150,000 variable stars are known and documented, and as many as thousands more are speculated to be variable.
  • They change brightness due to several reasons.
  • For example, pulsating variables shrink and swell due to internal forces.
  • An eclipsing binary will dim when obscured by a faint partner and then brightens when the occulting partner moves away.
  • The different causes for light variation in variable star render stimulus for classifying stars into different categories.

Types of Variable Stars

Types of Variable Stars
  • They are classified as intrinsic and extrinsic, depending on the cause of fluctuation.
    • Intrinsic – Physical changes such as pulsation or eruption in the star or cosmic system result in the variation
    • Extrinsic – Variability is induced by the eclipse of one star by another, the transit of an extrasolar planet, or by the effects of stellar rotation

Different Types of Intrinsic Variables Include

  • Pulsating variables
  • Eruptive variables
  • Cataclysmic or explosive variables

There Are Two Main Subgroups of Extrinsic Variables

  • Eclipsing binaries
  • Rotating stars


  • It is a cataclysmic stage towards the end of a star՚s life that is characterized by a sudden and dramatic rise in brightness.
  • A typical supernova may see a star become brighter by up to 20 magnitudes to an absolute magnitude of about -15. This means that a typical supernova may outshine the rest its galaxy for several days or a few weeks.
  • They are caused by one of two main mechanisms.
  • The first takes place when accreting material falling onto a white dwarf in a binary system takes it over the mass set by the Chandrasekhar limit.
  • The resulting instability triggers a runaway thermonuclear explosion that destroys the star and releases large amounts of radioactive and heavy elements into space.
  • The second process occurs in very massive stars once all the material in their core has been fused into iron. As fusion cannot occur in elements heavier than iron the drop in outwards radiation pressure means that gravitational collapse overwhelms the core which rapidly implodes.

Observations of Variable Stars

  • A pair of binoculars or a telescope
  • Variable star chart to help you navigate
  • Some basic instructions
  • A little patience
  • All of this might seem like a lot to keep in mind. But with time, it becomes easier. Devoted variable star-gazers become so familiar with the procedures that they cover dozens of stars a night swinging from one star to another without the help of charts.

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