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The Milky Way, just like every galaxy in the cosmos, moves. While everything in the universe is constantly moving because the universe itself is expanding, since the 1970s astronomers have known of an additional motion, called peculiar velocity. This is a different sort of flow that we seem to be caught in. The Local Group of galaxies — a collection that includes the Milky Way, Andromeda and a few dozen smaller galactic companions — moves at about 600 kilometers per second with respect to the leftover radiation from the Big Bang. Over the past few decades, astronomers have tallied up...

The Milky Way galaxy is at least 50 percent larger than is commonly estimated, according to new findings that reveal that the galactic disk is contoured into several concentric ripples. The research, conducted by an international team led by Rensselaer Polytechnic Institute Professor Heidi Jo Newberg, revisits astronomical data from the Sloan Digital Sky Survey which, in 2002, established the presence of a bulging ring of stars beyond the known plane of the Milky Way. "In essence, what we found is that the disk of the Milky Way isn't just a disk of stars in a flat plane—it's corrugated," said...

Explanation: What happens when a star runs out of nuclear fuel? For stars about the mass of our Sun, the center condenses into a white dwarf while the outer atmospheric layers are expelled into space and appear as a planetary nebula. This particular planetary nebula, pictured above and designated Shapley 1 after the famous astronomer Harlow Shapley, has a very apparent annular ring like structure. Although some of these nebulas appear like planets on the sky (hence their name), they actually surround stars far outside our Solar System.

Astronomers have determined the density and speed of dark matter in our corner of the universe. The finding helps bring dark matter out of the realm of the hypothetical and places scientists a few steps to closer figuring out what this invisible stuff that pervades the universe and holds galaxies together is made of. It also settles once and for all the question of which galaxy—our Milky Way or Andromeda—is more massive. The winner: The Milky Way.

Explanation: How big is our universe? This question, among others, was debated by two leading astronomers in 1920 in what has since become known as astronomy's Great Debate. Many astronomers then believed that our Milky Way Galaxy was the entire universe. Many others, though, believed that our galaxy was just one of many. In the Great Debate, each argument was detailed, but no consensus was reached. The answer came over three years later with the detected variation of single spot in the Andromeda Nebula, as shown on the original glass discovery plate digitally reproduced here. When Edwin Hubble compared images,...