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Beyond the Solar System
Cosmology: The Whole Universe
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The universe began with a fiery Big Bang. Matter and energy interacted with gravity and other fundamental forces to form the earliest structures. Over billions of years, the building blocks of the cosmos -- galaxies, galaxy clusters, giant walls, and voids -- have evolved. The study of that evolution may allow us to predict what the future will bring. More »

Age of the Universe
Temperature variations in leftover radiation from the Big Bang mark sites where the first galaxies probably formed (red, yellow).
Most astronomers agree that the observable universe is somewhere between 13 billion and 14 billion years old. More » 		Dark Matter
In galaxy cluster CL0024+1654, each yellow dot is a galaxy. Astronomers calculated the distribution of invisible dark matter (blue).
In the universe, what you see is certainly not what you get. More »
Great Dates

1543
Copernicus' De revolutionibus places the Sun, rather than Earth, at the center of the universe

1610
Galileo explains that the Milky Way is made up of stars, advocates that the Sun is just another star

1929
Edwin Hubble discovers that galaxies are moving away from each other, implying an expanding universe

1965
Arno Penzias and Robert Wilson discover the cosmic microwave background, supporting the Big Bang theory

1970
Vera Rubin and Kent Ford discover dark matter is an important part of the Andromeda galaxy

2001
The Hubble Key Project measures the expansion rate of the universe, which implies its age is 13 billion years

2002
Astronomers find evidence that the expansion of the universe is speeding up, pehaps goaded by 'dark energy'

Dark Energy
Most of the universe is invisible.
The universe seems to be pervaded with a previously unknown, and still unexplained, "dark energy." More » 		Measuring the Universe
Galaxy cluster Abell 2218.
Ongoing research by Texas astronomers and others helps us understand the age and size of the universe. More »
See Also...

Keywords about galaxies and cosmology

FAQs about galaxies and cosmology

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