Please vote for the TWO best Astronomy Pictures of the Day (image and text) of September 18-24, 2011.
(Repeated APODs are not included in the poll.)
All titles are clickable and link to the original APOD page.
We ask for your help in choosing an APOW as this helps Jerry and Robert create "year in APOD images" review lectures, create APOM and APOY polls that can be used to create a free PDF calendar at year's end, and provides feedback on which images and APODs were relatively well received. You can select two top images for the week.
We are very interested in why you selected the APODs you voted for, and enthusiastically welcome your telling us why by responding to this thread.
What created the circular structure around the south pole of asteroid Vesta? Pictured above, the bottom of the second largest object in the asteroid belt was recently imaged for the first time by the robotic Dawn satellite that arrived last month. A close inspection of the 260-meter resolution image shows not only hills and craters and cliffs and more craters, but ragged circular features that cover most of the lower right of the 500-kilometer sized object. Early speculation posits that the structure might have been created by a collision and coalescence with a smaller asteroid. Alternatively, the features might have originated in an internal process soon after the asteroid formed. New clues might come in the next few months as Dawn spirals down toward the rocky world and obtains images of increasingly high resolution.
Illustrated Video Credit: NASA, JPL-Caltech, T. Pyle; Acknowledgement: djxatlanta
If you stay up long enough, you can watch both suns set. Such might be a common adage from beings floating in the atmosphere of Kepler 16b, a planet recently discovered by the space-based Kepler satellite. The above animated video shows how the planetary system might look to a visiting spaceship. Although multiple star systems are quite common, this is the first known to have a planet. Because our Earth is in the orbital plane of both stars and the planet, each body is seen to eclipse the others at different times, producing noticeable drop offs in the amount of light seen. The frequent eclipses have given Kepler 16b the most accurate mass and radius determination for a planet outside our Solar System. To find a planet like Saturn in an orbit like Venus -- so close to its binary star parents -- was a surprise and will surely become a focus of research.
Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it like this: all dusty. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The above exposure took about 30 hours and covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.
Linking spiral arms, two large colliding galaxies are featured in this remarkable cosmic portrait constructed using image data from the Hubble Legacy Archive. Recorded in astronomer Halton Arp's Atlas of Peculiar Galaxies as Arp 272, the pair is otherwise known as NGC 6050 near center, and IC 1179 at upper right. A third galaxy, likely also a member of the interacting system, can be spotted above and left of larger spiral NGC 6050. They lie some 450 million light-years away in the Hercules Galaxy Cluster. At that estimated distance, the picture spans over 150 thousand light-years. Although this scenario does look peculiar, galaxy collisions and their eventual mergers are now understood to be common, with Arp 272 representing a stage in this inevitable process. In fact, the nearby large spiral Andromeda Galaxy is known to be approaching our own galaxy and Arp 272 may offer a glimpse of the far future collision between Andromeda and the Milky Way.
September's equinox arrives today at 0905 UT. As the Sun crosses the celestial equator heading south, spring begins in the southern hemisphere and autumn in the north. And though the seasonal connection is still puzzling, both spring and autumn bring an increase in geomagnetic storms. So as northern nights grow longer, the equinox also heralds the arrival of a good season for viewing aurora. Recorded earlier this month, these curtains of September's shimmering green light sprawl across a gorgeous night skyscape. In the foreground lies Hidden Lake Territorial Park near Yellowknife, Northwest Territories, Canada. Calm water reflects the aurora, with bright star trails peering through the mesmerizing sky glow. Of course, shining at altitudes of 100 kilometers or so, planet Earth's auroras are visible from space.
From Sagittarius to Carina, the Milky Way Galaxy shines in this dark night sky above planet Earth's lush island paradise of Mangaia. Familiar to denizens of the southern hemisphere, the gorgeous skyscape includes the bulging galactic center at the upper left and bright stars Alpha and Beta Centauri just right of center. About 10 kilometers wide, volcanic Mangaia is the southern most of the Cook Islands. Geologist estimate that at 18 million years old it is the oldest island in the Pacific Ocean. Of course, the Milky Way is somewhat older, with the galaxy's oldest stars estimated to be over 13 billion years old. (Editors note:This image holds the distinction of being selected as winner in the Royal Greenwich Observatory's Astronomy Photographer of the Year competition in the Earth and Space category.)
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