8.3.1 Evidence for the Expanding Universe

• How do red-shift observations support the expansion of the universe?

  Galaxies are moving away
• Hubble's Law relates the recession velocity of a galaxy to its distance.
• Cosmic microwave background radiation is another evidence supporting the expanding
• Spectral lines are specific wavelengths of light emitted or absorbed
• What is the direction of shift in red-shift?

  Longer wavelengths
• Red-shift occurs when an object is moving towards the observer.

  False
• An object moving towards the observer causes a blue-shift.
• What is the impact of red-shift on the color of light?

  Light appears redder
• Order the steps in calculating red-shift using spectral lines

  1️⃣ Identify emitted wavelength

  2️⃣ Identify observed wavelength

  3️⃣ Calculate red-shift using the formula
• What is the formula for calculating red-shift?

  $z =$$\frac{\lambda_{\text{observed}} - \lambda_{\text{emitted}}}{\lambda_{\text{emitted}}}$
• Blue-shift indicates that an object is moving away from the observer.

  False
• How are spectral lines used to measure red-shift?

  Comparing observed to reference spectra
• If the emitted wavelength is 500 nm and the observed wavelength is 525 nm, the red-shift value is 0.05.
• What is the direction of shift in blue-shift?

  Shorter wavelengths
• Hubble's Law states that the recession velocity of a galaxy is directly proportional to its distance.
• What happens to the red-shift value as the distance to a galaxy increases?

  Increases
• Galaxies farther away have a higher red-shift due to their greater recession velocities.
• What does red-shift indicate about the movement of galaxies?

  They are moving away
• Red-shift occurs when light from galaxies is shifted towards longer wavelengths
• Red-shift observations are the primary evidence for the expansion of the universe.
• What does a large red-shift value indicate about a galaxy's recession velocity?

  High recession velocity
• Farther galaxies exhibit smaller red-shifts compared to closer galaxies.

  False
• Red-shift observations suggest galaxies are receding from each other, supporting the expanding universe theory.
• What is the formula for Hubble's Law?

  $v =$$H_{0} d$
• Match the variable in Hubble's Law with its meaning:

  $v$ ↔️ Recession velocity

  $H_{0}$ ↔️ Hubble constant

  $d$ ↔️ Distance to galaxy
• Hubble's Law implies that galaxies are moving apart at a constant rate.
• The Cosmic Microwave Background is electromagnetic radiation left over from the early universe.
• What is the approximate temperature of the Cosmic Microwave Background?

  2.725 K
• Match the evidence with what it supports:

  Red-shift ↔️ Expansion of galaxies

  CMB ↔️ Early universe expansion
• Red-shift occurs when an object is moving towards the observer.

  False
• What is the formula for calculating red-shift using wavelengths?

  z = \frac{\lambda_{\text{observed}} - \lambda_{\text{emitted}}}{\lambda_{\text{emitted}}}</latex>
• Blue-shift occurs when light shifts towards shorter wavelengths.
• Red-shift is the shift in the spectrum of light towards longer wavelengths.
• Which law describes the relationship between red-shift and the distance of galaxies?

  Hubble's Law
• What does red-shift indicate about a celestial object's movement?

  Moving away from us
• The formula for calculating red-shift is z = (\lambda_{\text{observed}} - \lambda_{\text{emitted}}</latex>) / $\lambda_{\text{emitted}}$
• Galaxies farther away from us have higher red-shift values and greater recession velocities
• What is the relationship between red-shift and the distance of galaxies according to Hubble's Law?

  Higher red-shift implies farther distance
• Hubble's Law states that the recession velocity of galaxies is proportional to their distance
• The formula for Hubble's Law is $v =$$H_{0} d$