why is it difficult to measure the Hubble constant?

Suppose you have obtained spectra of several galaxies and have measuerd the observed wavelength of the H-Alpha line (rest wavelength = 656.3 nm) to be Galaxy 1: 658.1 nm. Galaxy 2: 667.1 nm. Galaxy 3: 677.6 nm. Assuming a Hubble Constant of 72.5 km/s/Mpc, calculate the distance to each of these galaxies (answer in Mpc)

A galaxy is observed to recede at speed 140 km/s. If the Hubble constant is 70 km/s/ Mpc, how far is the galaxy?

Calculate the Hubble constant for a universe that is 20 billion years old.

The Virgo cluster has a distance of about 17 Mpc from the earth. Using Hubble's law, determine the recessional velocity Vr to this cluster.

A new astronomical measurement suggests that the Hubble constant is 51 kilometers per second per Megaparsec. If this measurement is correct, what would the Hubble time be in units of years? Is this a plausible value based on other astronomical evidence? Why or why not?

Figure 2 shows the "rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 -4 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should…