Because of the cosmological expansion, a particular emission from a distant galaxy has a wavelength that is 2.00 times the wavelength that emission would have in a laboratory. Assuming that Hubble’s law holds and that we can apply Doppler-shift calculations, what was the distance (ly) to that galaxy when the light was emitted?

In the reading, you were told that there were roughly 10,000 galaxies in the image of the Hubble Ultra Deep Field alone. The image is roughly 10 square arcminutes and there are roughly 1.5*10^8 square arcminutes composing the entire sky. With that in mind and assuming that the Hubble Ultra Deep Field represents an average part of the sky, roughly how many galaxies may exist in the observable universe? (Please include commas for every factor of 1,000; for example 2,343,567,890)

why is it difficult to measure the Hubble constant?

With the aid of a diagram, explain the physical origin of cosmological redshift in an expanding universe, and how this differs from the Doppler shift due to relative motion. Observations of distantgalaxies indicate that their recession velocities, v, and their distances, d, follow a Hubble Law:v = H0d, where H0 is a constant. Using the analogy of an expanding grid or ruler, demonstratethat Hubble’s Law indicates that the Universe is undergoing uniform expansion.