Astronomy Concepts in Pictures

The images on these pages tell the story of what we have learned about the Universe, and how we learned it.

At the beginning of astronomy, we watched the sky, tracking the regular motions of the Sun, Moon, and stars. Although we didn't know what these objects were, we saw that their motion was regular, and that they could guide us as to when to hunt, plant, and reap. We imbued the heavenly bodies with power, and imagined that they also might allow us to understand other aspects of our lives &mdash love, health, and fortune.

Scientific inquiry, arguably starting with the Greeks, then the Arabs, and finally re-discovered by Europeans, revealed more about our Universe. Copernicus and Galileo found evidence that the Earth was not the center of the Universe. This solidified an idea that had been around for a while, that the Sun and stars were objects in a physical Universe, rather than as heavenly bodies apart from the Earth.

The big breakthrough was the discovery that the stars were objects like our Sun, except vastly more distant. This realization allowed astronomers to determine the structure of our own Galaxy. Then, in the 1920s, Edwin Hubble was able to prove that our Galaxy is just one of many in the Universe.

The 20th century brought a flood of discoveries in all areas of physics, and these continue to shape our understanding of the cosmos. One of the great theories of the 20th century was Einstein's theory of General Relativity, which describes the relationship between mass, energy, gravity, and the structure of space and time. General Relativity was used to explain Hubble's observation that distant galaxies were all moving away from us. Thus, we discovered that the Universe was expanding and evolving.

The other great theory of the 20th century was quantum mechanics, which describes the structure of the sub-atomic world. Using quantum mechanics, astrophysicists were able to understand how stars live and die.

Today, astronomers are studying a wide range of topics. They are exploring the planets of our own Solar System, and searching for planets around distant stars. They are learning how stars form and what happens after they die. They are trying to understand how galaxies change as the Universe ages. They are trying to understand what matter, besides that which we can touch on Earth, makes up the bulk of the Universe, in hopes of better understanding fundamental physics.

These pictures tell part of that story.

I found most of the images on this site on the Astronomy Picture of the Day archive. Even as an astronomer, I found that site to be an excellent resource for finding the best examples of images to represent well-know phenomena, and sometimes for discovering new things. I also took some images from the public outreach sites of NASA's great observatories: Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope. Each image that I used has the link to the original source underneath.

The top image on each screen is detail from "Io: The Prometheus Plume" (Credit: Galileo Project, JPL, NASA), and the bottom image from "Jupiter Eclipsing Ganymede" (Credit: NASA, ESA, and E. Karkoschka (U. Arizona)).

Most of the text was composed from memory, based on the courses I took as an undergraduate and graduate student, from various other lectures at universities and conferences, and from papers I've read. You get bonus points if you can figure out which topics I actually did research in (hint: the descriptions are too long). I intend to look through some popular astronomy books, to fill in any gaps.

I learned how to format the pages from tutorials on the W3 Consortium site, and from the CSS Zen Garden.

The site is currently under construction. I expect that there are errors in it, particularly when it comes to any historical statements (I was only present for the very recent stuff!), and of course grammer puncuation and, spelling. Feel free to send comments to mtspaceblog at gmail. I am considering: (1) adding some more concise summaries to the images, (2) splitting off some of the more involved discussion so that I don't mix very basic and more advanced information quite so much, (3) changing the order, (4) making some thumbnail images so the pages load faster, and (5) perhaps finding a tool that will let users vote on their favorite images or topics.

Last modified: Sun Aug 2 20:26:42 EDT 2009