Measure of a star s brightness. Stellar propertiesMagnitude - PowerPoint PPT Presentation

Title: Measure of a star s brightness. Stellar propertiesMagnitude


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Color
Brightness/Magnitude
Star Properties
Temperature
Mass
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Measure of a stars brightness.
Apparent magnitude brightness as it appears
from Earth
Absolute magnitude true brightness if star was
viewed from 10 parsecs - scale ranges from -15
to 15
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• Hot stars
• Temp above 20,000C
• Emits short high energy wavelength (BLUE)

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• Medium stars
• Temp between 5000 6000 C
• Stars appear yellow

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Cool stars -Temperature less than 3000 C -
Emits low energy wavelengths (RED)
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Mass of stars are based on the mass of our Sun
1/10 of solar mass, OR 50X solar mass, etc.
The more massive the star, the quicker it burns
through its hydrogen. Most important property
in determining star life cycle!!!
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1 astronomical unit (AU) 93 million miles
(Earth to Sun) - used in our solar system
One light year (ly) is the distance light travels
in one year (9.5 trillion km)
One parsec (pc) is trigometric distance of
changing the parallax angle by one arcsecond 1
parsec (pc) is equivalent to 206,265 AU
3.26 Light Years 3.086x1013 km
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Stellar parallax apparent shift in a stars
position due to the orbital motion of the earth.
Video
Parallax is measured as an angle based on two
measurements. The greater the angle the closer
the star.
This is accurate up to about 1000 parsecs (1 of
the diameter of the Milky Way)
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Cepheids are variable stars that brighten and dim
at regular intervals (period)
Period and brightness (magnitude) are related, so
if we know absolute brightness we can determine
distance
This is accurate up to about 50 million light
years using the Hubble or Chandra telescopes
(less than 15 ly for telescopes on Earth)
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At large distances, individual stars are too
small to see.
Supernovae are visible, and their absolute
magnitude is known (-19.3 for type 1A), so a
calculation between absolute and apparent
magnitude can be made
Useful up to 1 billion light years away
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At very large distances (gt 1 billion ly),
Hubbles law, and the redshift must be used.
A diffracted image taken at two different times
will show a shift in the red direction as it
moves away which can then be calculated
v H x d - H hubbles constant approximately
65km/sec
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• Two stars held together by gravity orbit around
  each other
• More than 50 of stars are binary (Alpha Centauri
  A B)

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Because galaxies are moving (remember the red
shift Hubble raisin bread mentioned above)
collisions among galaxies are also thought to
have played an important role in present day
galaxies
Galaxies come in several shapes, often influenced
by collisions, including spiral (Milky Way),
elliptical, barred spiral, and irregular shaped
galaxies.
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• Supermassive black holes have the mass of many
  millions of suns
• Located in the centers of the most galaxies.

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• Quasi-stellar radio source - Caused by the
  accretion disc around supermassive black holes
• Most powerful, luminous object in the universe
  located in the centers of the most distant
  galaxies.
• Characteristic of an actively feeding black
  hole
• - the Milky Way does not have a quasar

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Accretion disk

• 100 million light years from earth

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• 4.6 billion light years from earth

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Ripples in cosmic background radiation
distances of supernovas create problems
Basically, dark stuff is the remainder of an
equation or the answer to an unexplainable
phenomenon
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Dark Matter Does not give off light, but has
gravity ? (makes about 23 of the universe
compared to 4 for the matter we are made of.)
Explains the remainder of matter needed for
observed gravity
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• Dark Energy acts like a force that opposes
  gravity and pushes galaxies apart at an
  increasing rate.

Perhaps 70 of the universe according to NASA
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• Universe Dark Energy-1 Expanding Universe. This
  diagram shows changes in the rate of expansion
  since the Universe's birth 14 billion years ago.
  The more shallow the curve, the faster the rate
  of expansion. The curve changes noticeably about
  7.5 billion years ago, when objects in the
  Universe began flying apart at a faster rate.
  Astronomers theorize that the faster expansion
  rate is due to a mysterious, dark energy that is
  pulling galaxies apart. Credit NASA/STSci/Ann
  Feild