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"I want to know why the universe exist, why there is something greater than nothing."
Steven Hawking
Scientist, Space Lover
Our Universe is expanding. Distant galaxies appear to recede from us at ever-increasing speeds. What is the rate of expansion? How long has it been expanding? What will be its ultimate fate? Two groups of astronomers are searching vigorously for answers to these fundamental questions using the Hubble Space Telescope (HST). The teams have recently announced conflicting measurements of the Hubble constant, a number which represents the expansion rate of the Universe. Astronomer Wendy Freedman and her collaborators have used pulsating stars called Cepheids to measure the distance to galaxies like the Fornax cluster barred spiral galaxy NGC1365 shown above. The ground based photo (left) shows an inset locating the HST image (right) which Freedman and team have used to identify some 50 Cepheids. Their distance and velocity measurements determine Hubble's constant to be about 80 kilometers per second per megaparsec which means that galaxies one megaparsec (3 million lightyears) distant appear to recede from us at a speed of 80 kilometers per second. Conflicting results indicating a substantially slower expansion rate (smaller Hubble constant) are being reported by astronomer Allan Sandage and collaborators. The value of Hubble's constant was recently the subject of a popular public debate titled "The Scale of the Universe 1996: The Value of Hubble's Constant".
NGC 1808 is a galaxy in turmoil. A barred spiral with marked similarities to our home Milky Way Galaxy, NGC 1808 is distinguished by a peculiar nucleus, an unusually warped disk, and strange flows of hydrogen gas out from the central regions. Amidst all of this, NGC 1808 is undergoing so much star formation it has been deemed a starburst galaxy. In the above color-enhanced photograph, regions of active star formation and shown by their blue glow. Here bright blue stars have recently formed and are energizing large clouds of surrounding hydrogen gas. The reddish brown regions indicate dense interstellar dust. NGC 1808 is a relatively close 40 million light-years away, and stretches about 35,000 light-years across. The peculiar state of NGC 1808 may be caused by the gravity of neighboring galaxy NGC 1792.
It was one of the quietest nights of aurora in weeks. Even so, in northern- Iceland during last November, faint auroras lit up the sky every clear night. The featured 360-degree panorama is the digital fusion of four wide-angle cameras each simultaneously taking 101 shots over 42 minutes. In the foreground is serene Lake Myvatn dotted with picturesque rock formations left over from ancient lava flows. Low green auroras sweep across the sky above showing impressive complexity near the horizon. Stars far in the distance appear to show unusual trails -- as the Earth turned -- because early exposures were artificially faded. Follow APOD on: Facebook, Google Plus, or Twitter
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