16 ONTENT C Cassini was approximately 2.2 million km New Images from the Cassini from Saturn when the images in this mosaic on the cover were acquired. Image scale on Saturn is Spacecraft about 260 km per pixel. Superb Janus The above image shows Janus, Saturn’s curious small moon, visible against the cloud- streaked backdrop of the giant planet. Unlike our moon, Janus (181 km across) On Monday, 4 December 2006, is irregular in shape, i.e., it resembles a It is believed that large portions of Helene showers occurred in Alexandria gigantic potato! Many minor planets and have been blasted away by meteoritic in the evening. I observed the rain, hoping to photograph a planetary moons are too small to attain a impacts. rainbow. No rainbows appeared, round shape. but actually, I encountered my Cassini flew by Helene on 17 August 2006, first tornado! There are many craters on the surface of when these images were acquired, at a Janus, but some areas seem to have been distance of about 50,000 km. The series of smoothed by some geological process. Like images were recorded over the course of Pandora and Telesto, Janus is believed to one hour. be covered with a mantle of fine dust-sized Helene (32 km across) is co-orbital with icy material. Dione (1,120 km across), the second densest Editorial The image was taken using a spectral of Saturn’s moons. Dione is believed to be filter sensitive to wavelengths of infrared composed of rock and ice. NASA recently published the following Huygens announced that there are rings 4 light centered at 930 nanometers. The view In 2004, Cassini discovered another superb images of Saturn and its moons, surrounding Saturn. was acquired with the Cassini spacecraft small co-orbital moon, Ploydeuces. acquired by the Saturn-bound Cassini narrow-angle camera on 25 September 2006, spacecraft. Seven major rings have been named Supervisor at a distance of approximately 145,000 km Further reading A through G, in order of discovery. They The Universe Now from Janus and at a Sun-Janus-spacecraft, The Janus/Epimetheus Ring In Saturn’s Shadow contain several gaps, due to the gravitational Hoda Elmikaty or phase, angle of 62 degrees. North on http://www.nasa.gov/mission_pages/cassini/multimedia/ influence of some of Saturn’s moons. Director 5 Saturn is up. Image scale is 871 meters per pia08322.html This is a unique image of Saturn. The Moon-Made Rings Planetarium Science Center pixel. Cassini spacecraft was flying in the shadow Saturn’s rings are composed of ice and http://www.nasa.gov/mission_pages/cassini/multimedia/ of Saturn, viewing the planet’s glorious dust. They contain fine microscopic dust pia08328.html Editors Helene’s Close-up rings as never seen before. particles, best viewed when the Sun is The Cassini-Huygens Mission Aymen Ibrahem directly behind Saturn. The distribution of Hot Topic The images show Saturn’s small, peculiar http://saturn.jpl.nasa.gov/home/index.cfm The picture reveals previously unknown PSC Senior Astronomy Specialist these particles provides information about moon Helene. The images were obtained Helene.jpg faint rings, and even shows our home planet the space environment of the planet. by the Saturn-bound Cassini spacecraft, 162056main_PIA08329.jpg from afar. It is a composite of 165 images and they show the bizarre, rugged terrain Janus.jpg obtained by Cassini on 15 September 2006, The outermost ring, the E ring, is Maissa Azab encircling the entire ring system. The narrow of Helene. PIA08329.jpg when it flew beyond Saturn for 12 hours. PSC Publications Specialist G ring is visible between the E ring and the Cassini detected two new rings; one main bright rings. The E ring is believed to Bibliotheca Alexandrina Fun Fact coincident with the shared orbit of the have originated due to volcanic eruptions Planetarium Science Center moons Janus and Epimetheus, and another on the surface of the icy, geologically active P.O. Box: 138, Chatby, 11 Alexandria 21526, Egypt. along the orbit of the tiny moon Pallene. moon Enceladus. Tel.: +(203) 4839999 The rings were discovered by Galileo in Earth was over a billion km from Saturn Ext: 1451 1610, but he failed to perceive their shape during the observation. It is visible as a pale Fax: +(203) 4820464 Picture Gallery with his small telescope. In 1655, observing dot, interior to the G ring, and above the [email protected] with a more powerful telescope, Christian bright main rings. www.bibalex.org/psc 12 14 3 2 15 Cassini was approximately 2.2 million km from Saturn when the images in this mosaic were acquired. Image scale on Saturn is about 260 km per pixel. Superb Janus The above image shows Janus, Saturn’s curious small moon, visible against the cloud- streaked backdrop of the giant planet. Unlike our moon, Janus (181 km across) is irregular in shape, i.e., it resembles a It is believed that large portions of Helene gigantic potato! Many minor planets and have been blasted away by meteoritic planetary moons are too small to attain a impacts. round shape. Cassini flew by Helene on 17 August 2006, There are many craters on the surface of when these images were acquired, at a Janus, but some areas seem to have been distance of about 50,000 km. The series of smoothed by some geological process. Like images were recorded over the course of Pandora and Telesto, Janus is believed to one hour. be covered with a mantle of fine dust-sized Helene (32 km across) is co-orbital with icy material. Dione (1,120 km across), the second densest The image was taken using a spectral of Saturn’s moons. Dione is believed to be filter sensitive to wavelengths of infrared composed of rock and ice. light centered at 930 nanometers. The view In 2004, Cassini discovered another was acquired with the Cassini spacecraft small co-orbital moon, Ploydeuces. narrow-angle camera on 25 September 2006, at a distance of approximately 145,000 km Further reading from Janus and at a Sun-Janus-spacecraft, The Janus/Epimetheus Ring or phase, angle of 62 degrees. North on http://www.nasa.gov/mission_pages/cassini/multimedia/ Saturn is up. Image scale is 871 meters per pia08322.html pixel. Moon-Made Rings http://www.nasa.gov/mission_pages/cassini/multimedia/ Helene’s Close-up pia08328.html The Cassini-Huygens Mission The images show Saturn’s small, peculiar http://saturn.jpl.nasa.gov/home/index.cfm moon Helene. The images were obtained Helene.jpg by the Saturn-bound Cassini spacecraft, 162056main_PIA08329.jpg and they show the bizarre, rugged terrain Janus.jpg of Helene. PIA08329.jpg 2 15 Picture Gallery The Universe Now By Aymen Ibrahem Hubble Explores Negative Gravity 1 Credit: NASA, ESA and A. Riess and Credit: NASA, ESA Formation Scientists observing with the Hubble to rule out competing explanations that This is the first photo Ibrahem obtained. It is a close-up showing the formation of the tornado. Space Telescope (HST) have discovered predict that the influence of dark energy Actually, the twister grew rapidly! evidence that dark energy, a hypothetical changes over time. form of energy that pervades the entire The researchers also arrived at an Universe and counteracts gravity, is not interesting conclusion that the type of a new characteristic of space, but rather exploding stars, or supernovae, used to has been acting for most of the Universe’s history. determine cosmic distances today look remarkably similar to those that exploded Dark energy is believed to accelerate nine billion years ago and are just now being 2 the rate of cosmic expansion, discovered by detected by Hubble. This important finding Edwin Hubble in the 1920s. In his theory of provides additional support to the use of General Relativity, Albert Einstein introduced these supernovae for tracking the cosmic a cosmological constant to achieve a model expansion through most of the evolution of Tornado Develops of a static Universe. Einstein, however, the Universe. The tornado develops. Few passers abandoned this constant after Hubble’s were on the Plaza. discovery of the expansion of the Universe, Supernovae provide reliable distance calling it “greatest blunder”. measurements because their brightness variation and intrinsic brightness are well 3 In 1998, researchers used HST and studied. They are therefore reliable distance ground-based telescopes to detect the indicators, enabling astronomers to acceleration of the expansion of space determine their vast distances from Earth. from observations of distant supernovae. Astrophysicists realized that Einstein may These Hubble images reveal five have been correct after all, as there appeared supernovae in distant galaxies. The arrows to be a negative gravity in space that was in the top row of images point to the subsequently dubbed “dark energy”. supernovae. The bottom row shows the host galaxies, before or after, the stars The researchers used Hubble to find exploded. The supernovae exploded that dark energy was already increasing between 3.5 billion and 10 billion years the expansion rate of the Universe as long ago. TornadoTornado Close-upClose-up as nine billion years ago (The Universe is This is a close-up photo showing the swirling Further reading winds of the tornado. believed to be about 14 billion years old). Hubble Finds Evidence for Dark Energy in the Young Universe The tornado grew considerably in size. Hubble’s data would allow cosmologists http://hubblesite.org/newscenter/archive/releases/2006/52/full/ 12 5 Picture Gallery The Universe Now Editorial By Aymen Ibrahem Hubble Explores Negative Gravity 4 A CloseClose EncounterEncounter withwith a .... 1 Credit: NASA, ESA and A. Riess and Credit: NASA, ESA Formation Scientists observing with the Hubble to rule out competing explanations that This is the first photo Ibrahem obtained.