The Difference Between Astronomy, Astrophysics and Cosmology

Astronomy is the study of what you see in the sky and the dynamics of objects in space. I think of it as about what you can see when you observe the sky with your eyes or through a telescope. What I love about astronomy is that it is accessible to everyone. You walk outside on a clear night and you can participate in astronomy

This is the age of the great space observatories and all their incredible pictures are available to all on the web, like the Hubble Gallery.

We are also in the age of personal astronomy. With a simple telescope, digital camera, free software and the right techniques, anyone can create stunning astronomy photographs to be proud of. Not quite like the Hubble, but pretty cool non the less.

Astrophysics is about why the objects in the heavens behave the way they do, usually about stellar and galactic processes. It touches on plasma physics, nucleosynthesis, electromagnetics, gravitation, and relativity, just to name a few areas. So much of what we see in the stars we can replicate in the lab- the physics of the stars is the physics on our desktop.

But, with the extreme environments we observe in space, we can push the envelope of our understanding of physics. The greatest explosions in the universe occur in supernova, the most precise measurements to test gravitational theories are from closely orbiting neutron star pulsars, and the origin of life itself may lay in the nucleosynthesis of stars, how they seed the interstellar space with elements and how these elements coalesce into dust, organic molecules and planets.

Cosmology is about the origin, evolution and large scale structure of the universe. The physics of the universe from the first picosecond (10^-12), to the present, is quickly being fleshed out. The standard model of fundamental particles including quarks, leptons and neutrinos condensed out first. By the end of the first three minutes, the primordial nucleosynthesis and elemental abundances were established. After 400,000 years, matter and radiation decoupled leaving behind the cosmic microwave background (CMB) radiation. Since then, matter condensed into stars, black holes, galaxies and the large scale clumpy structure we see today.

In the last thirty years, there has been an explosion in observational evidence that supports the current Big Bang theory but has opened up new questions. What drove inflation, why did the four known forces condense as they did, when they did, what is the nature of dark matter, what is the nature of dark energy, what is the precise evolutionary path of galaxies from the clumping of primordial gas, the first stars and galactic size black holes, and the role of collisions in shaping the distribution of the galaxies we see today.

In this rich field of physics, there is something for everyone.