Related Experiment Video
Updated: Jul 8, 2026

Bringing the Visible Universe into Focus with Robo-AO
Published on: February 12, 2013
Abstract:
Modern distance determinations to galaxies were reviewed and placed on a uniform and self-consistent scale. Based on eight separate but not entirely independent techniques, the distance to the Virgo cluster was found to be 15.8 +/- 1.1 megaparsec. Twelve different determinations yield a Coma/Virgo distance ratio of 5.52 +/- 0.13 and hence a Coma distance of 87 +/- 6 megaparsec. With a cosmological redshift of 7210 kilometers per second, this gives a Hubble parameter H(0) (local) of 83 +/- 6 kilometers per second per megaparsec. From the velocity-distance relation of rich clusters of galaxies, the ratio of the value of H(0) (global) to the value of H(0) (local) was determined to be 0.92 +/- 0.08. In other words, the cluster data do not show a statistically significant difference between the local and global values of the Hubble parameter. If one nevertheless adopts this relation between H(0) (global) and H(0) (local), then the value of H(0) (global) is 76 +/- 9 kilometers per second per megaparsec. This observed value differs at the approximately 3sigma level (where sigma is the standard deviation of the distribution) from values in the range 36 less, similar H(0) less, similar50 kilometers per second per megaparsec, which are derived from stellar evolutionary theory in conjunction with standard cosmological models with a density parameter (Omega) that is equal to 1 and a cosmological constant (lambda) that is equal to 0.
Related Concept Videos
Orders of Magnitude
The order of magnitude is simply a way of rounding numbers consistently to the nearest power of 10. This makes doing rough mental math...
Circular Orbits and Critical Velocity for Satellites
Nicolaus Copernicus (1473-1543) first suggested that the Earth and all other planets orbit the Sun in...
Kepler's First Law of Planetary Motion
Polish astronomer Nikolaus Copernicus put forth a theory that stated a heliocentric model for the solar system. According to this heliocentric theory, all the planets, including Earth, orbit the Sun in circular orbits.
On the other hand,...
Kepler's Third Law of Planetary Motion
Schwarzschild Radius and Event Horizon
The minimum speed required to launch a projectile from the surface of an object to which it is gravitationally bound so that it eventually escapes the object’s gravitational field is called the escape velocity. The escape velocity is independent of the mass of the object. Merging the idea of escape velocity with the...
Space-Time Curvature and the General Theory of Relativity
This has been verified in many experiments. However, space and time are no longer absolute. Two observers moving relative to one another do not agree on the length of objects or the passage of time. The mechanics of objects based on Newton's laws of motion,...

