The Hubble constant is calculated by comparing distance values to the apparent recessional velocity of the target galaxies — that is, how fast galaxies seem to be moving away. The team’s calculations give a Hubble constant of 69.8 km/sec/Mpc — straddling the values derived by the Planck and Riess teams.

From observations of the apparent magnitudes of the brightest stars in 14 more nebulae, Hubble estimated their distances. Comparing this value with the apparent magnitudes of the stars in four nebulae in the still more distant Virgo Cluster of galaxies, he determined their distance too.

What assumptions do we make when we use the Hubble constant to estimate the distance to a galaxy? The red shifts of the galaxies imply that the universe is expanding and that we are at the center. Most of the elements heavier than helium were made during the first few minutes after the big bang.

‘Red shift’ is a key concept for astronomers. The term can be understood literally – the wavelength of the light is stretched, so the light is seen as ‘shifted’ towards the red part of the spectrum. Something similar happens to sound waves when a source of sound moves relative to an observer.

It is often expressed by the equation v = H0D, with H0 the constant of proportionality—Hubble constant—between the “proper distance” D to a galaxy, which can change over time, unlike the comoving distance, and its speed of separation v, i.e. the derivative of proper distance with respect to cosmological time coordinate …

1. a) Astronomers use the parallax method to measure the distance to nearby stars, but we can’t use it to measure the distance to stars in other galaxies.

The errors quoted are one sigma, with the first being the statistical error, and the second, larger error being the systematic uncertainty due to factors like the chemical composition of the Cepheids in different galaxies, the distance to the Large Magellanic Cloud to which the distance comparison is made, and the …

WMAP Can Measure the Age of the Universe In turn, knowing the composition with this precision, we can estimate the age of the universe to about 0.4%: 13.77 ± 0.059 billion years!

Edwin Hubble

When Hubble did this, he found that the recession velocity of the galaxies tended to increase with their distance. Fitting a straight line to the data, he wrote down a formula that we now call Hubble’s Law: V = H0D. This simple equation is one of the most important formulas in all astronomy (indeed, in all science).

Today the value is still rather uncertain, but is generally believed to be in the range of 45-90 km/sec/Mpc. While in general galaxies follow the smooth expansion, the more distant ones moving faster away from us, other motions cause slight deviations from the line predicted by Hubble’s Law.

The exact value of the Hubble constant is still somewhat uncertain, but is generally believed to be around 65 kilometers per second for every megaparsec in distance.

Hubble’s Law is the relation between the recession velocity of a galaxy and its distance: Vr = H d, that is, the velocity of recession Vr equals the distance d times the Hubble constant H.

Acceleration of the Universe For a given value of H, we know the recession velocity of any two points separated by some distance at a given time. At a later time, these two points will have increased their distance, and hence — by Hubble’s law — their recession velocity will have increased.

In his short paper, Hubble presented the observational evidence for one of science’s greatest discoveries—the expanding universe. Hubble showed that galaxies are receding away from us with a velocity that is proportional to their distance from us: more distant galaxies recede faster than nearby galaxies.