Hubble Space Telescope: History and Discoveries
that Changed Our View of the Universe   or   index.html

  The Big Bang model was a natural outcome of Einstein's
  General Relativity as applied to a homogeneous universe.
  However, in 1917, the idea that the universe was expanding
  was thought to be absurd. So Einstein invented the
  cosmological constant as a term in his General Relativity
  theory that allowed for a static universe.

  In 1929, Edwin Hubble announced that his observations of
  galaxies outside our own Milky Way showed that they were
  systematically moving away from us with a speed that was
  proportional to their distance from us. The more distant
  the galaxy, the faster it was receding from us. The
  universe was expanding after all, just as General
  Relativity originally predicted!

  Hubble observed that the light from a given galaxy was
  shifted further toward the red end of the light spectrum
  the further that galaxy was from our galaxy.

  The specific form of Hubble's expansion law is important:
  the speed of recession is proportional to distance.

       Hubble Constant  =  71.0  2.5 km/s/Mpc



  The Big Bang has no center. It is space (the universe as
  a whole) that is expanding, so everywhere is equally the

Cepheid Variable Stars

  Explanation: In the 1920s, examining photographic plates from
  the Mt. Wilson Observatory's 100 inch telescope, Edwin Hubble
  determined the distance to the Andromeda Nebula, decisively
  demonstrating the existence of other galaxies far beyond the
  Milky Way. His notations are evident on the historic plate
  image inset at the lower right, shown in context with ground
  based and Hubble Space Telescope images of the region made
  nearly 90 years later. By comparing different plates, Hubble
  searched for novae, stars which underwent a sudden increase in
  brightness. He found several on this plate, indicating their
  position with lines and an "N". Later, discovering that the
  one near the upper right corner was actually a type of
  variable star known as a cepheid, he crossed out the "N" and
  wrote "VAR!". Thanks to the work of Harvard astronomer
  Henrietta Leavitt, cepheids, regularly varying pulsating
  stars, could be used as standard candle distance indicators.
  Identifying such a star allowed Hubble to show that Andromeda
  was not a small cluster of stars and gas within our own
  galaxy, but a large galaxy in its own right at a substantial
  distance from the Milky Way. Hubble's discovery is responsible
  for establishing our modern concept of a Universe filled with

  Henrietta Leavitt Calibrates the Stars


  Working at Harvard College Observatory, Leavitt precisely
  calibrated the photographic magnitudes of 47 stars to which
  all other stars could be compared. Leavitt discovered and
  cataloged over 1500 variable stars in the nearby Magellanic
  Clouds. From this catalog, Leavitt discovered that brighter
  Cepheid variable stars take longer to vary, a fact used today
  to calibrate the distance scale of our universe.

  NGC 4414: A Telling Spiral
  The Cepheids of M100

Minute Physics - 
Henry Reich, Perimeter Institute for Theoretical Physics

A Polarizing Discovery About the Big Bang!

What Is The Universe?

Do We Expand With The Universe?

How Big is the Universe?

Veritasium - Derek Muller

Misconceptions About the Universe

Astronomy Picture of the Day Archive