FRIENDS OF THE PLANETARIUM NEWSLETTER – SEPTEMBER 2014The European Space Agency's Rosetta spacecraft finally arrived at Comet 67P/Churyumov-Gerasimenko a month ago, after a 10-year cruise through interplanetary space. In an ideal world, Comet C-G would have been a nice smooth ball of dust and ice with a big X marking the safest and most scientifically interesting landing site for the craft's Philae lander. Had that been the case, says Rosetta mission manager Fred Janssen, his team would have put the odds of a successful landing at 70 or 75 percent. However, nature has thrown the project a few

curves. Not only is the comet's nucleus complicated, an irregular, double-lobed structure 4 km long, but it's also much rougher and craggier than expected. The recently taken image at left shows how irregularly shaped the comet really is. This photo was taken from a distance of about 30 km. Add to that the comet's ahead-of-schedule activity (it's already giving off jets of gas despite being 3.4 astronomical units from the Sun), and all bets are off. At an ESA press briefing Janssen declined to offer a revised risk assessment. "No site meets all the engineering criteria," he allowed. That said, Philae has to set down someplace, and the team has winnowed down an initial set of 10 candidate sites to primary and backup locations. The best location, designated Site J, is on the comet's smaller lobe (think of it as the "head"); the backup, Site C, is on the larger "body." Engineers opted to stay clear of the smooth-textured "neck"

between them, because from there it would be difficult for Philae to remain in constant radio contact with the main spacecraft as it orbits the nucleus. The smaller-lobe site won out in part because cameras have already identified two small pits near it that are sources of outgassing. Each of Philae's 10 instruments will be able to operate at least once to its full capability. Assuming no "gotchas" emerge, the spacecraft will release Philae on November 11th for its 7-hour-long "fall" to the comet's surface. Once it makes contact at roughly one meter per second), the washing-machine-size, 100-kg lander will anchor itself using a mechanical harpoon, then quickly take a 360 degree panorama and measure the pressure of cometary gas surrounding it. The photo above right shows details of the chosen landing site. It still looks quite dodgy but we all wish ESA great success.A total eclipse of the moon takes place on October 8. All phases of the eclipse are visible from New Zealand. Totality lasts for almost an hour from 11:25 pm to 12:24 pm. The moon starts entering the Earth's umbral shadow about 10:15 pm and finally leaves it at 1.35 am. Uranus is at opposition on October 8th, the planet will then be 2844 million km, 19 AU, from the Earth. Consequently the planet will be in the sky all night.  It is currently in Pisces. A few hours after Uranus is at opposition the Earth's moon is in total eclipse. Uranus, at magnitude 5.7 will be 2 degrees above the moon as seen from NZ. A similar magnitude star will be 1.3 degrees to the left of Uranus; otherwise there is no object likely to be confused with Uranus in binoculars above the moon.

NASA's Pluto-bound New Horizons spacecraft has traversed the orbit of Neptune. This is its last major crossing en route to becoming the first probe to make a close encounter with distant Pluto on July 14, 2015.The sophisticated piano-sized spacecraft, which launched in January 2006, reached Neptune's orbit, nearly 4.4 billion kilometers from Earth, in a record eight years and eight months. New Horizons' milestone matched precisely the 25th anniversary of the historic encounter of NASA's Voyager 2 spacecraft with Neptune on Aug. 25, 1989. "It's a cosmic coincidence that connects one of NASA's iconic past outer solar system explorers, with our next outer solar system explorer," said Jim Green, director of NASA's Planetary Science Division. "Exactly 25 years ago at Neptune, Voyager 2 delivered our 'first' look at an unexplored planet. Now it will be New Horizons' turn to reveal the unexplored Pluto and its moons in stunning detail next summer on its way into the vast outer reaches of the solar system." Several senior members of the New Horizons science team were young members of Voyager's science team in 1989. Many remember how Voyager 2's approach images of Neptune and its planet-sized moon Triton fueled anticipation of the discoveries to come. They share a similar, growing excitement as New Horizons begins its approach to Pluto. Similar to Voyager 1 and 2's historic observations, New Horizons also is on a path toward potential discoveries in the Kuiper Belt, which is a disc-shaped region of icy objects past the orbit of Neptune, and other unexplored realms of the outer solar system and beyond.Once every 50 years, more or less, a massive star explodes somewhere in the Milky Way. The resulting blast is terrifyingly powerful, pumping out more energy in a split second than the sun emits in a million years. At its peak, a supernova can outshine the entire Milky Way. It seems obvious that you wouldn't want a supernova exploding near Earth. Yet there is growing evidence that one did, actually, more than one. About 10 million years ago, a nearby cluster of supernovas went off like popcorn. We know because the explosions blew an enormous bubble in the interstellar medium, and we're inside it. Astronomers call it "the Local Bubble." It is peanut-shaped, about 300 light years long, and filled with almost nothing. Gas inside the bubble is very thin (0.001 atoms per cubic centimeter) and very hot (roughly a million degrees), a sharp departure from ordinary interstellar material. The Local Bubble was discovered gradually in the 1970s and 1980s. Optical and radio astronomers looked carefully for interstellar gas in our part of the galaxy, but couldn't find much in Earth's neighborhood. Meanwhile, x-ray astronomers were getting their first look at the sky using sounding rockets and orbiting satellites, which revealed a million-degree x-ray glow coming from all directions. It all added up to Earth being inside a bubble of hot gas blown by exploding stars. Obviously, those supernovas were not close enough to exterminate life on Earth, but they were close enough to wrap our solar system in a bubble of hot gas that persists millions of years later.Do you know where you live? You probably know your street address and the name of your town, region, and country. But what about your cosmic address, your location among the stars? Thanks to efforts by some astronomers in Hawaii, you can now tell people you live in Laniakea. Scientists have known for decades that our solar system rests on an outer arm of the Milky Way galaxy. In turn, galaxies are not sprinkled randomly throughout the cosmos; they cluster into groups, which themselves are part of larger groups. What has been known is our Milky Way is part of the Local Group, a collection of galaxies some 10 million light-years across. Based on work by Gerard de Vaucouleurs in the 1950s, astronomers have thought of our galaxy as being on the edge of the so-called Local Supercluster, a structure about 100 million light-years wide that’s centered on the Virgo Cluster of galaxies. Now, a team of scientists led by University of Hawaii astronomer R. Brent Tully have mapped the boundaries of a massive "supercluster" of galaxies stretching 500 million light-years through space. They named the supercluster "Laniakea," a Hawaiian word meaning "immense heaven." As a side benefit to identifying a new structure in the universe, the largest yet known, the team's efforts shed light on what's called the Great Attractor. Scientists have known of a perturbation in the general cosmic expansion, a "pull" towards a particular part of the sky, for 40 years, and for nearly 30 have known in what direction it lies. Its nature, though, has remained a mystery. The mapping of Laniakea enables astronomers to conceptualize the Great Attractor as the basin of a gravitational "valley", the end point of the supercluster's watershed.