8.2.1 Galactic Red-shift

• What is the phenomenon of red-shift?

  Red-shift refers to the stretching of light wavelengths, making them appear redder.
• Why does red-shift occur?

  It occurs when an object emitting light moves away from the observer.
• How is red-shift related to the Doppler effect?

  Red-shift is similar to the Doppler effect for sound, where the frequency changes based on the object's movement relative to the observer.
• What happens to light when an object moves away from the observer?

  The light stretches into longer, redder wavelengths.
• What is blue-shift?

  Blue-shift occurs when an object moves towards the observer, causing its light to shift to shorter, bluer wavelengths.
• What does galactic red-shift indicate?

  Galactic red-shift indicates that galaxies are moving away from us.
• What is the significance of galactic red-shift in cosmology?

  It provides evidence for the expanding universe model.
• Who observed the relationship between distance and red-shift in galaxies?

  Edwin Hubble observed this relationship.
• What does Hubble's Law state?

  Hubble's Law states that the velocity at which a galaxy recedes is directly proportional to its distance from us.
• What is the formula for Hubble's Law?

  $v =$$H_0 \times d$
• What does the Hubble constant (\( H_0 \)) represent?

  The Hubble constant represents the rate of expansion of the universe.
• What is the approximate value of the Hubble constant?

  It is roughly around 70 km/s per megaparsec (Mpc).
• How do astronomers measure red-shift?

  Astronomers use spectroscopy to analyze the spectrum of light from a galaxy.
• What do spectral lines indicate in red-shift measurements?

  Specific lines in the spectrum shift towards the red end, indicating how much the light has been stretched.
• What is the formula to calculate red-shift (\( z \))?


  $z =$$\frac{\lambda_{observed} - \lambda_{emitted}}{\lambda_{emitted}}$
• What does the observation of red-shift support in cosmology?

  It supports the Big Bang theory, indicating that the universe has been expanding since its inception.
• How does red-shift relate to the expansion of the universe?

  Red-shift shows that the universe is expanding everywhere in space.
• How does red-shift help cosmologists?

  It helps them understand the rate of expansion and estimate the size, age, and future of the universe.
• What is the current estimated age of the universe?

  About 13.8 billion years.
• What are the key points about red-shift and its implications?

  • Red-shift is the stretching of light to longer wavelengths as an object moves away.
  • Galactic red-shift indicates galaxies are receding, providing evidence for the expanding universe.
  • Hubble's Law relates red-shift to distance, showing the universe's expansion rate.
  • Spectroscopy measures red-shift, helping determine galaxy velocities and supporting the Big Bang theory.
  • Understanding red-shift is essential for grasping the universe's evolution.