Hubble Constant

Hubble Constant: 70.8 km/s per mega-parsec.

The Math / Science

The Hubble Constant is the unit of measurement used to describe the expansion of the universe. The value of the Hubble Constant is important for both observations of the objects in the Universe, as it allows us to convert their recession velocities into true distances, and for estimating the age of the Universe. Hubble Constant  has units of km/sec per megaparsec (km/s/Mpc).

In the 1920's, Edwin Hubble working with observations from the Mount Wilson Observatory discovered that the Universe is expanding. He compared recession velocities of galaxies measured from their spectra to their apparent brightness estimated from photographic plates. This expansion causes objects at greater and greater distances to be receding from us at higher and higher speeds, at a velocity given by an expression now known as Hubble's Law: V = H x R. Here V represents the galaxy's recessional velocity, R is its distance away from Earth, and the constant of proportionality, H, is called the Hubble Constant and has units of km/sec per megaparsec (km/s/Mpc). The value of the Hubble Constant is important for both observations of the objects in the Universe, as it allows us to convert their recession velocities into true distances, and for estimating the age of the Universe.

One Mega-Parsec is approximately equal to:

• 30,856,770,000,000,000,000 kilometers
• 19,173,507,963,493,200,000 miles
• 206,264,767,389 astronomical units (au)
• 3,261,632 light years

Slowing Down to Speeding Up

As more of the universe was observed from Edwin Hubble's time through the 20th century, the observable light and the implied volume of the universe and implied matter within the universe led scientist to the conclusion that the expansion of the universe was slowing.  Using the volume, mass and the force of gravity, this was a logical conclusion.  However, the Supernova Cosmology Project at Lawrence Berkley National Laboratory made a startling discovery.  Led by PhD cosmologist, Saul Perlmutter, their study of Type 1a supernova provided strong evidence that contrary to the mathematical certainty that universal expansion was slowing, evidence showed that the universe was indeed expanding an accelerating rate!  The implications is that, against the force of gravity, another force is certainly pushing the expansion of the universe outward.  This force is what's commonly now known as Dark Matter/Dark Energy.  This discovery led to Perlmutter, Brian Schmidt, and Adam Riess being awarded the Nobel in Physics in 2015.  The picture below shows Perlmutter in the middle with Director of Lawrence Berkley National Laboratory, Michael Witherell on the right and vCalc's founder Kurt Heckman on the left. 

Astronomy Calculators

• Hubble's Law
  • Hubble Constant Formula
  • Hubble Constant with Units
• Kepler's 3^rd Law formula T² = (4π • R³)/(G • M)
  • (M) - mass of the system. 
  • (T) - period of the orbit.
  • (R) - separation distance between the two objects.
  • (G) - universal gravity constant
• Small Angle Formula
  • (α) - angle
  • (D) - distance to astronomical object
  • (S) - size or diameter of astronomical object
• Flux and Magnitude formulas
  • Change in Magnitude from Flux Ratio
  • Flux Ratio from Magnitudes
• Telescope formulas
  • Resolving Power of a Telescope
  • Magnification of a Telescope
• Mass formulas
  • Mass from Luminosity
  • Mass from Acceleration and Radius
  • Mass from Speed and Separation
  • Mass of extra-solar planet from mass of star, radius of star orbit and radius of exoplanet orbit
  • Mass of extra-solar planet from mass and velocity of star and velocity of planet
• Relative Size Formulas
  • Relative Size from Relative Temperature and Luminosity
  • Relative Temperature from Relative Size and Luminosity
  • Relative Luminosity from Relative Temperature and Size
• Wavelength Formulas
  • Velocity from shift in Wavelength and Unshifted Wavelength
  • Wavelength Shift from Wavelength and Speed
  • Blackbody Wavelength from Temperature
  • Blackbody Temperature from Peak Wavelength
  • Photon Energy from Wavelength
  • Photon Wavelength from Energy
• Luminosity and other Formulas
  • Distance from absolute and apparent magnitude
  • Radius from Speed and Period
  • Speed of Circular Motion
  • Hubble Time
  • Luminosity from Mass

Related Astro Calculators:

• Kepler's 3^rd Law Calc has Kepler's 3^rd law solved for each parameter.
• Astronomy Calculator contains basic formulas for a college level Introduction to Astronomy
• Exoplanet Calculator contains formulas for studying planets outside of our Solar System.
• Astronomical Distance Calculator provides the distance from the Earth to numerous astronomical bodies (e.g. Sun, Moon, planets, stars, Milky Way's Center and Edge, Andromeda Galaxy)
• Astronomical Distance Travel Time Calculator computes the time to travel to distant parts of space at different velocities.
• Ellipse Calculator
• 3D Vector Calculator:
• Drake Equation Calculator
• Seager Equation Calculator
• Friedman Equation Calculator
• Exoplanet Calculator contains formulas for studying planets outside of our Solar System.
• Astronomical Distance Calculator provides the distance from the Earth to numerous astronomical bodies (e.g. Sun, Moon, planets, stars, Milky Way's Center and Edge, Andromeda Galaxy)
• Astronomical Distance Travel Time Calculator computes the time to travel to distant parts of space at different velocities.
• Radius of Perigee
• Radius of Apogee