Unit 10 Space 5

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Unit 10 Space 5

• Constellations
• Absolute and Apparent Magnitude
• Measurement in Space
• Light-Year as a Measurement Unit
• Star Light Spectra

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Guiding Questions Space 5

• What is a constellation? (p.704) How many
  constellations are there? (p.705)
• How do the constellations appear to move across
  the sky? (p.705)
• What is absolute magnitude? What is apparent
  magnitude? How are they different? (p.706)
• How is the distance to stars measured? (p.707)
• What is a light-year? (p.707)
• What can scientists learn from the light spectra
  of stars? (p.708)

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1. What is a constellation? How many
constellations are there?

• A constellation is a pattern of stars in the sky.
  Ancient cultures in Europe and the Middle East
  named the constellations for mythological
  characters or animals that the patterns
  resembled. Most of the constellations we
  recognize today were named centuries ago.
• Today, astronomers recognize 88 different
  constellations as a way of naming different
  regions of the sky, and for numbering the stars
  within each region.

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1. Constellations (cont.)

• The stars in constellations appear to be near one
  another in the sky, but in fact, they usually are
  far apart in space.

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2. How do the constellations appear to move
across the sky?

• In the northern hemisphere, the stars appear to
  rotate counter-clockwise around a point directly
  above the north pole. At the present time, a
  star named Polaris, or the North Star, is very
  close to this rotation point. Polaris is located
  in the constellation commonly called the Little
  Dipper, or Ursa Minor (meaning Little Bear)
  by astronomers.

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2. Constellation Movement (cont.)
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3. What is absolute magnitude? What is apparent
magnitude? How are they different?

• The absolute magnitude of a star is a measure of
  how much light it actually gives off.
• The apparent magnitude of a star is a measure of
  the amount of light received on Earth from the
  star.
• In other words, the absolute brightness of a star
  is not dependent on the viewpoint, while the
  apparent brightness is the brightness from a
  particular viewpoint, Earth.

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4. How is the distance to stars measured?

• Scientists use different methods to estimate the
  distance from a star to Earth. For stars that
  are relatively close to Earth, a method called
  parallax shift is used. The change in position
  of the star against the backdrop of more distant
  stars is measured as the Earth travels around the
  Sun. The greater the apparent shift, the closer
  the star is to Earth. The amount of shift in
  degrees can be converted to distance by a simple
  formula.

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5. Parallax (cont.)
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5. What is a light-year?

• A light-year is a unit of measurement used by
  astronomers for very large distances, like the
  distances between stars and galaxies. It is the
  distance that light travels in one year in a
  vacuum. Since light travels about 300,000 km per
  second, it travels about 9,500,000,000,000 (9.5
  trillion) kilometers in one year. The closest
  star to our Sun is Proxima Centauri, about 4.3
  light-years away.

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6. What can scientists learn from the light
spectra of stars?

• The light from stars can be collected in a large
  telescope and passed through a prism or
  diffraction grating to split the light into its
  component colors (its spectrum). Since each
  element gives off a unique set of colored light
  bands when it emits light, and absorbs those same
  wavelengths when it hit with light, scientists
  can tell exactly what a star is made of from its
  light spectra.