Stars and Their Characteristics

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Stars and Their Characteristics
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Constellations

• A group of stars that appear to form a pattern in
  the sky
• Is the big dipper the largest?
• No
• Ursa Major (big bear)

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Circumpolar constellations

• These never set below the horizon and can be seen
  all year long

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Seasonal changes in constellations

• Some like the big dipper only change the position
  in the sky
• Others can only be seen during certain seasons

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Summer Sky
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Fall Sky
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Winter
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Spring Sky
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Distance to Stars

• Astronomical Unit (AU) - 150 million kilometers,
  which defines the distance between the sun and
  earth
• Light Year (LY) this is a unit of distance, not
  a unit of timethe distance that a ray can travel
  in one yeara ray can travel 9.5 trillion
  kilometers in 1 year

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Elements in Stars

• Using a spectrum analysis stars contain mainly
• Hydrogen
• Helium
• Trace amounts of the following
• Oxygen
• Carbon
• Nitrogen
• Calcium
• Sodium
• and others

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What is used to figure this out?
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Star Brightness

• Apparent magnitude How bright / dim a star
  looks here on Earth
• Luminosity actual true brightness
• Depends on the size and temperature
• Absolute magnitude the luminosity of stars
  assuming the same distance

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Stars comparison
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Different kinds of Stars

• Sun
• Giants
• Supergiants

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Red Giants

• Cooler large red stars

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Supergiants

• Stars that are hundreds of times more luminous
  than the red giants
• Examples
• Blue-white Rigel
• White Yellow Canopus
• Antares and Betelgeuse
• Red Supergiants are the largest of all stars

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Dwarf stars

• These stars have a very low luminous (lower then
  1)
• Colors
• Orange
• Red
• Yellow
• Exceptions white dwarf
• These are very faint, very small, very dense
• These stars are the same size as the Earth BUT
  100000 times more dense than Earth

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Merging of two white dwarfs
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Sun

• Which category does the sun fall into?
• Why
• What will happen to the Earth as the Sun ages?

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Variable Stars

• Stars that usually shine with the same
  brightness, but there are times where for days or
  even years the brightness may vary

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Pulsating stars

• Stars that change in brightness as they expand
  and contract.
• Examples
• Cepheid / variables are yellow supergiants
  whose brightness changes from 1 to 50 days at a
  time

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Nonpulsating Stars

• Stars that appear to be changing in brightness,
  but instead of being one star you are really
  looking at two stars of unequal brightness
  (together these two stars form an eclipsing
  binary)

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Pulsars

• When one star emits both light and radio waves
  which to us look like a flickering of the star

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Formation of Stars
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Origin of a Star

• Nebulas clouds of gas and dust
• Diffuse nebula
• Dark nebula

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How do the Stars age?
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Red Giants

• The energy inside this star is used up allowing
  gravity to become unbalanced
• This allows the core to expand

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White Dwarfs

• When the fuel is used up and the temperature and
  pressure inside the star is unable to support the
  weight of the outer layers
• Causing the inside to shrink
• Occasionally they may flare up brightening
  themselves many times over

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Supernovas

• As the star decays in inner core collapses
  causing an explosion so violently that half its
  mass is blown away as a great cloud.

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Neutron Stars and Black Holes

• The mass that remains after the explosion of the
  Supernova is called a neutron star.
• When the nuclear forces between the neutrons are
  overwhelmed, the star collapses and becomes a
  black hole.

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Collisions of two neutron Stars
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Black holes