... An Unexpected Flare from the Crab Nebula . ... Credit Copyright: NASA , DOE , Fermi LAT , R. Buehler ( SLAC , KIPAC ) Explanation: Why does the Crab Nebula flare? ... As recently as one month ago, gamma-ray observations of the Crab Nebula by the Fermi Gamma Ray Space Telescope showed an unexpected increase in gamma-ray brightness, becoming about five times the nebula's usual gamma-ray brightness, and fading again in only a few days. ... Publications with keywords: Crab Nebula - gamma ray . ...

... Bad Astronomy . ... Bitesize Astronomy . ... Last week's Snack talked about how black holes can affect the environment around them in such a way as to be very bright . ... It's a common misconception that black holes always have matter swirling into them. ... As this matter gets closer and closer to the black hole it piles up and a large, fairly flat disk forms. This is called the accretion disk , because matter from this disk accretes (that is, falls in) on the black hole. ... 2008 Phil Plait. ...

... Jitter is usually very small in magnitude and random in effect, and is not expected to lead to systematic throughput changes. ... However, such a change should lead to an obvious decline in the strength of the comparison lines at one end of the spectrum relative to the other and not an overall decline in counts. No such effect is seen (the counts decline evenly from one end of the spectrum to the other). ... The value changes steadily, but not by enough to account for the changes in counts seen. ...

... 2010 September 6 . A Laser Strike at the Galactic Center . ... Explanation: Why are these people shooting a powerful laser into the center of our Galaxy? ... Constant imaging of high-altitude atoms excited by the laser -- which appear like an artificial star -- allow astronomers to instantly measure atmospheric blurring . ... In this case , a VLT was observing our Galaxy's center , and so Earth's atmospheric blurring in that direction was needed. ... About APOD | ...

. " The Arecibo Observatory is sponsored by the National Science Foundation. Any opinions, findings and conclusions or recommendations . expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation."

... Tonight's Sky . ... The Magazine . ... Observing . ... The double star 54 Leonis, spiral galaxy NGC 3198, and emission nebula NGC 3199 . ... Astronomy for Kids . ... Observing springtime deep-sky objects with a large telescope . ... Bright planets meet at dusk . ... Astronomy magazine subscribers can read the full article for free. ... Get instant access to subscriber content on Astronomy.com! ... Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter....

... 2000 March 12 . Supernova 1994D and the Unexpected Universe . Credit: High-Z Supernova Search Team , HST , NASA . Explanation: Far away, long ago, a star exploded. ... Supernova 1994D was not of interest for how different it was, but rather for how similar it was to other supernovae . ... The large number and great distances to supernovae measured over the past few years have been interpreted as indicating that we live in a previously unexpected universe . ... About APOD | ...

A team of U.S. and German astrophysicists have made the first ever detection of X-rays coming from a comet. ... Following the initial detection, the team reported repeated X-ray emissions from the comet over the next 24 hours. ... One preliminary theory is that X-ray emission from the Sun was absorbed by a cloud of gaseous water molecules surrounding the nucleus of the comet, and then were re-emitted by the molecules in a process physicists call "fluorescence." ... Comets . ...

... Green ESO . ... Observations made using the HARPS spectrograph at ESOтАЩs La Silla Observatory in Chile have revealed unexpected changes in the bright spots on the dwarf planet Ceres. Although Ceres appears as little more than a point of light from the Earth, very careful study of its light shows not only the changes expected as Ceres rotates, but also that the spots brighten during the day and also show other variations. ... ArtistтАЩs view of bright spots on Ceres imaged by the Dawn spacecraft . ...

... Next, the screen displays "Press 0 to align or Mode for Menu." Press "0" if you wish to begin Automatic alignment (or Easy Align, depending on your telescope model), or press Mode if you wish to choose a manual alignment method ("Automatic Alignment" displays, and you can press MODE to go through the menu to find other alignments). ... Note: If you press the "?" key while "Ctr Brightest Star" displays, the alignment star that AutoStar has chosen will display. ... Alignment successful" displays. ...

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