Just as astronomers were getting used to the idea of not knowing what dark matter is, they got a completely different surprise at the end of the 20th century. Instead of slowing down after the Big Bang, the expansion of the Universe was found to be accelerating. Astronomers quickly did what they always do when they come up with something mysterious: they gave it a name. Now, we call whatever it is pushing the Universe apart "dark energy", but the truth is no one knows what it is.

When you look up at the night sky, you see a lot of things glowing like stars, planets, and galaxies. So it might sound strange to hear that most of the Universe is actually dark. The truth is the protons, neutrons and electrons that make up everything we can see - and that means with every telescopes we've got -- accounts for only about 4% of the mass and energy of the Universe. The rest is dark and mysterious. More specifically, about 70% of the Universe is what is known as dark energy; about 26% is so-called dark matter.

Hello! Hopefully by now you'll have read a little about 3C 321, aka the "Death Star Galaxy" from

Dr. Dan Evans from the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA, shares some information on 3c321, as of December 2007 now known as the Death Star Galaxy. Dan Evans has never seen Star Wars, so who came up with the nickname? Read on.

The press and image releases from the Chandra X-ray Center cover only a small fraction of the science results produced by Chandra each year. Some results are clearly not good candidates for publicity because they're obviously incremental - I've written papers like that myself. Or they can be highly esoteric, addressing questions that only the authors knew enough about the subject to ask! It also doesn't help if the results are completely unsurprising or if there isn't a decent image.

The detectors we use on Chandra are different from detectors on optical telescopes. Most of the Chandra images are taken with what's known as a Charged Coupled Device (CCD). The CCD is the type of detector that's in the camera in your cell phone, or in your digital camera.

Shown from left: Chandra X-ray image of supernova remnant G292.0+1.8, Chandra X-ray image of young star cluster Westerlund 2, and a multiwavelength view of galaxy M82 (Chandra X-ray, Spitzer Infrared, Hubble Optical).

Last week, the American Astronomical Society held its bi-annual meeting in Austin, TX. (The AAS, as it's known, always has a winter meeting in early January and then a spring meeting around Memorial Day.) The AAS meetings are important because the AAS is the largest professional group of astronomers in the US and so they often bring some of their most exciting results to share.

Explore the Universe from your computer using Sky in Google Earth. The latest version of Sky in Google Earth, released on January 9, 2008, now contains X-ray images from NASA's Chandra X-ray Observatory. Pictured: Cas A and M82. Learn more about Sky in Google Earth

The latest version of Sky in Google Earth, released on January 09, 2008 at the American Astronomical Society meeting in Austin, Texas, now contains X-ray images from NASA's Chandra X-ray Observatory. Along with images from other NASA satellites, the addition of Chandra into Sky in Google Earth provides scientists, students, and amateur stargazers new opportunities to explore the Universe across the electromagnetic spectrum. Eli Bressert, Image Processor at the Chandra X-ray Center, discusses the Sky in Google Earth update.

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