COSMOLOGY

 

Stellar Parallax

·         Copernicus said it couldn’t be seen because the stars were so far away.

·         In 1838 Friedrich Bessel found parallax and used it to measure stellar distances.

·         61 Cygnus A had a parallatic angle of 0.2 arc seconds.

·         Made it 100,000 times more distant than Saturn

·         Prior belief: The stars were as far beyond the planets as the planets were beyond the sun.

 

Cepheid Variables

·         Stars that vary in brightness every few days

·         Caused by a tug of war between gravity and the outward pressure of star light

·         Time between dimmest to brightest depends on strength of light pressure – i.e., how bright a star really is.

·         Relative brightness = absolute brightness/square of distance

·         Distance as measured by Cepheid variables:

·         In 1912, Henrietta Leavitt (American astronomer) used Cepheids to measure the distance to the Large and Small Magellanic Clouds (Nebulae in the southern sky discovered by Magellan)

·         Found them 1000 times more distant than 61 Cygnus A

·         Therefore they had to contain millions of stars and be billions of light years across

Is the Universe Finite or Infinite?

·         Newton’s physics leads one to think infinite

·         Olbers’ Paradox

·         Heinrich Olbers, Swiss astronomer, in 1826 asked

·         Why is it dark at night?

 

Galaxy

·         gala = milk

·         galaktinos = milky

·         Galaxy = Milky Way

·         Are we part of the Milky Way?

·         Is our galaxy the only one?

·         Are distant nebulae really galaxies – other universes?

 

Edwin Hubble

·         American astronomer

 

Red Shift

·         Light from the spiral galaxies was shifted to the red end of the spectrum, i.e. long wave lengths

·         Suggests that the light source is moving away from us. The speed of motion is determined by the amount of red shift.

 

Hubble’s Constant

·         Hubble found that every galaxy had red shift, the farther the galaxy, the more the shift

·         Hubble’s constant H0 = distance/(red shift)

 

The Big Bang

·         If the universe is expanding, it must have been (much) smaller in the past.

·         It must have had a beginning.

·         Georges LeMaitre – Jesuit priest/astronomer used general relativity to construct a model of the universe which began as a “primeval atom” which exploded

·         Given the nickname (derisively), the Big Bang.

 

Cosmic Background Radiation

·         If there was a Big Bang, there would be a faint microwave radiation left over, of about 3 degrees Kelvin.

·         In 1964, Arno Penzias and Robert Wilson, two engineers at Bell Labs in New Jersey discovered this radiation when trying to get rid of noise from a telecommunications satellite.

 

Black Holes

·         When a large star burns out it falls in on itself

·         If big enough, it becomes so dense that a curvature of space around it becomes infinite. Not even light can escape.

·         It becomes a black hole (as predicted by general relativity).

·         The universe itself is like a black hole.

·         Maybe the universe is a black hole in some other universe.

 

The Big Crunch

·         Will the universe stop expanding? If so, then what?

·         If the amount of matter in the universe is above a critical amount, it will stop expanding one day and begin to contract, due to gravity.

·         The result will be The Big Crunch.

·         If not it will expand forever.