- RED SHIFT:
Astronomers often study the radiation (including ultraviolet light, visible light, and infrared radiation) coming from distant stars and galaxies.
Some of this radiation occurs in recognizable patterns that reflect the chemical identity of excited atoms at high temperatures.
Some of these recognizable patterns appear shifted toward the red (low frequency) end of the spectrum, so it is called the red shift.
- The red shift is best explained as a form of Doppler effect,
as explained here.
- HUBBLE EFFECT:
In the 1920s, American astronomer Edwin Hubble discovered that the "red shift" is greater for galaxies far away than for nearer galaxies,
meaning that far-away galaxies were moving away from us (and from one another) more rapidly than nearby galaxies.
This is sometimes called "Hubble's Law": the speed at which galaxies are moving apart is proportional to their distance from us.
- "BIG BANG" and the AGE OF THE UNIVERSE:
From the rate at which galaxies are moving apart, we can calculate how long ago it was before they began moving apart.
RESULTS OF THIS CALCULATION: All galaxies for which these calculations have been done all started out close together at about the same time in the past.
The best explanation for this result, and for the Hubble effect, is that the Universe originated in a great explosion, or "BIG BANG",
about 13.8 billion years ago (according to current estimates).
- Cosmic Background Radiation:
The "echo" or "residue" from the Big Bang is a Cosmic Background Radiation, mostly in the microwave portion of the spectrum.
The Cosmic Background Radiation shows that interstellar space has a temperature of about 3 Kelvin (3 K) rather than absolute zero (0 K).
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