2 Content on the cover NGC 3370, a dust-laden spiral galaxy. This galaxy shows intricate spiral arms, with hot areas of new star formation. The galaxy lies 98 million light years away, in the direction of the constellation Leo. In 1994, a massive star exploded in NGC 3370, outshining all other stars of the galaxy. Contents Editorial The New Solar System Supervisor The Universe Now Hoda Elmikaty Two Years at Saturn Naming Distant Moons Director Wonders of the Universe Planetarium Science Center Discovery Lands Safely Woman Space Tourist flies into Orbit Editors Hot Topic Aymen Ibrahem Starless Planets PSC Senior Astronomy Specialist Fun Fact Saturn Cartoon Picture Gallery Maissa Azab Ringed Crescent PSC Publications Specialist Solar Eclipses on Uranus Shining Blue Eyes Planetarium Science Center Bibliotheca Alexandrina P. O. Box: 138, Chatby, Alexandria 21526, Egypt. Tel.: +203 4839999 Ext. 1451 Fax: +203 4820464 [email protected] www.bibalex.org 3 Editorial The New Solar System Fig (1) The new Solar System Credit: NASA On Thursday, 24 August 2006, the As a result, the number of the planets in International Astronomical Union (IAU) approved the Solar System, shrunk to eight, starting with a new definition of the term “Planet”. Mercury and ending with Neptune. It is expected that the eight planets will be termed the “classical During the historic meeting of the IAU’s planets”. General Assembly in Prague, hundreds of astronomers, from all around the world, voted to For years, the status of Pluto has been adopt the new definition. debated. Since 1992, astronomers have discovered hundreds of icy objects orbiting the Sun in a belt The IAU is the authority responsible for beyond the orbit of Neptune. The existence of naming and classifying all the celestial objects. The these trans-Neptunian objects was predicted by IAU defines a planet as an object that orbits the the great Dutch-American astronomer Gerard Sun; its mass is large enough to attain a spherical Kuiper, through his studies of the orbits of the or nearly round shape; and has cleared its orbit of short-period comets. These objects are known as other objects. the Kuiper Belt Objects (KBOs). According to this definition, Pluto, formerly The KBOs appear to be similar to Pluto in the ninth and smallest planet, lost its planet composition (ice and rock), and some of them status, because its elliptical, highly inclined orbit have been found to be comparable to Pluto in size. overlaps with that of giant Neptune, and was thus Also, by planetary standards, Pluto (about 2,300 demoted to the newly devised class of “Dwarf km across) is a very small object. It is even smaller Planet”, including two other minor planets. A than our Moon (3,476 km across). So, some “Dwarf Planet” is defined as an object that orbits astronomers regarded Pluto as a giant KBO. the Sun and whose mass is large enough to attain a nearly round shape. Other than Pluto, the two Earth is over 500 times more massive than other dwarf planets are Ceres (about 1,000 km Pluto!! Pluto’s gravity is only 1/15 (about 7%) across) and Eris (about 2,400 km across). that of Earth, i.e., on Pluto, an astronaut’s weight 4 will be only 7% of his/her weight on Earth. Mars and Jupiter. At the time of its discovery, Pluto’s average distance from the Sun (nearly Ceres was regarded as a planet, but when it was 6,000 million km) is about 100 times larger than realized that it is one of many similar objects, it that of Mercury. It lasts 247.68 years to orbit was reclassified as a minor planet till 24 August Solar System the Sun once. Thus, Mercury that orbits the Sun 2006. Ceres orbits the Sun in an elliptical orbit, once every 88 days, is over 1,000 times faster than at an average distance of about 413.7 million km Pluto! from the Sun. It lasts approximately 4.6 years to orbit the Sun once. Pluto is also unique among the planets, as it has a large moon, Charon (about 1,200 km across). The total estimated number of asteroids is Charon is regarded the largest moon in the Solar about one million. Several hundred thousand System, relative to its parent planet. Actually, asteroids have been discovered and given Pluto and Charon orbit their common center of provisional designations. Thousands more are gravity, lying between the two objects. Therefore, discovered every year. Pluto was regarded by some astronomers as a The IAU also adopted a third class of Solar binary planet. The center of gravity of the Earth- System objects, known as Small Solar System Moon system lies beneath the Earth’s surface. Bodies SSSBs, including all the objects that are On 5 January 2005, a large trans-Neptunian not planets or dwarf planets (asteroids, KBOs, object was discovered by Dr. Mike Brown (Caltech) comets and meteoroids). and his colleagues, on images obtained in 2003 at Our new Solar System consists of eight planets, Palomar Observatory. The object was technically three dwarf planets, and numerous SSSBs. designated 2003 UB313 and nicknamed Xena by the discoverers. Recently, the IAU officially Some astronomers, colleagues and friends named this object Eris. Measurements based on of Clyde Tombaugh, the discoverer of Pluto, Hubble Space Telescope observations showed that protested the IAU’s decision to strip Pluto of Eris is slightly larger than Pluto. The discoverers its planetary status. Dr. Alan Stern, Principal and some astronomers had called it the “Tenth Investigator of the New Horizons spacecraft, which Planet”. was launched toward Pluto in January 2006, has been particularly involved in the controversy over As a result, it was realized that a definition the new definition of the term “planet”. Dr. Stern of the term planet was necessary, as astronomers is a planetary scientist who specializes in Pluto. would continue to discover more objects that are Online petitions have appeared, urging the IAU comparable to Pluto in size. to consider reinstating Pluto. Earlier, the IAU discussed a proposal that Personally, I agree with classifying Pluto as a would have raised the number of planets to dwarf planet. I always believed that it is a large 12, including Charon (Pluto’s KBO, not a planet, due to its orbit, size, largest moon), Eris (the largest composition and binary nature. A known trans-Neptunian few days after the vote, I gave a object), and Ceres (the largest public lecture entitled “The asteroid), but it was eventually New Solar System”, explaining rejected. the new definition of the term Ceres was discovered in “planet”, and describing the 1801 by Giuseppe Piazzi (1746- new classification of the Solar 1826). It is the largest asteroid. System objects. Interestingly, The asteroids (minor planets) the children who attended the are small, rocky objects that orbit lecture were not sad about Pluto! the Sun mainly between the orbits of They were only a little bit amazed! 5 The Universe Now rn Two Years at Satu Saturn, as imaged by Cassini Credit: NASA/JPL/Space Science Institute n 1 July 2004, the international Cassini Ospacecraft arrived at Saturn, beginning a Naming 4-year mission in orbit around the ringed giant. the New Moons of Pluto Cassini is the first spacecraft to orbit Saturn. Now Cassini is halfway through its historic mission. During these two years, Cassini has produced a wealth of stunning images, startling discoveries, topographic maps and myriads of measurements. Celebrating Cassini’s second anniversary, NASA’s Jet Propulsion Laboratory (JPL), published an interesting slide show on its website. View Show http://www.jpl.nasa.gov/multimedia/cassini-essay-4/ The Cassini-Huygens mission is a joint project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Credit: NASA/STScI Laboratory, a division of the California Institute of The two small satellites of Pluto, discovered May Technology, California, manages the mission for 2005, were officially named Nix and Hydra. The NASA’s Science Mission Directorate, Washington, IAU recently approved the names. DC. The Cassini orbiter and its two onboard cameras were designed, developed and assembled The names are so befitting for Pluto, formerly the at JPL. The imaging operations center is based at darkest and coldest planet. In Roman mythology, the Space Science Institute in Boulder, Colorado. Pluto was god of the Underworld. In Greek For additional information, please visit: mythology, Charon, Pluto’s largest known moon, http://saturn.jpl.nasa.gov. The Cassini imaging team was the boatman who ferries the souls of the homepage is at http://ciclops.org. dead to the Underworld. Nix was the goddess 6 of Darkness and mother of Charon. Hydra is a (NGC stands for the New General Catalogue of horrible beast: a serpent with nine heads. deep sky objects; this galaxy is the 5866th entry of the NGC.) Astronomers plan to make further observations of Nix and Hydra to study in detail their orbits and NGC 5866 is a “nearby” galaxy, located at a physical properties. distance of only 44 million light years. (The farthest objects in the Universe are estimated to be NASA’s New Horizons spacecraft, will map the over 13,000 million light years away.) It is 60,000 two moons when it arrives at Pluto in summer light years across, i.e., it is two-thirds the size of 2015. New Horizons might even discover more our Galaxy, but it has a comparable mass. moons of Pluto. A striking dust lane divides the galaxy into two Interestingly, as the first two letters of the word halves; it is slightly warped, indicating a past tidal Pluto honor Percival Lowell, the astronomer who interaction with another galaxy.