The Leonids (/ˈliːənɪdz/ LEE-ə-nidz) are a prolific meteor shower associated with the comet Tempel–Tuttle. The Leonids get their name from the location of their radiant in the constellation Leo: the meteors appear to radiate from that point in the sky. Their proper Greek name should be Leontids (Λεοντίδαι, Leontídai), but the word was initially constructed as a Greek/Latin hybrid and it has been used since. They peak in the month of November.
Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough – typically closer than Jupiter's orbit. The Leonids are a fast moving stream which encounter the path of Earth and impact at 72 km/s. Larger Leonids which are about 10 mm across have a mass of half a gram and are known for generating bright (apparent magnitude -1.5) meteors. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet.
The meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet. They are differentially disturbed by the planets, in particular Jupiter and to a lesser extent by radiation pressure from the sun, the Poynting–Robertson effect, and the Yarkovsky effect. These trails of meteoroids cause meteor showers when Earth encounters them. Old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids, that tends to peak around November 18, but some are spread through several days on either side and the specific peak changes every year. Conversely, young trails are spatially very dense and the cause of meteor outbursts when the Earth enters one. Meteor storms (large outbursts) exceed 1000 meteors per hour, to be compared to the sporadic background (5 to 8 meteors per hour) and the shower background (several per hour)....LESS
Encyclopedia of Planetary Landforms contains a description and interpretation of all known planetary landforms that have been discovered on the planetary bodies in our Solar System. The content is separated into entries for each planetary landform. All entries are based on literature reviews, using NASA/ESA/JAXA imagery and original general and thematic maps of the particular landform. Such a wide variety of landforms show how exotic these features could be from a terrestrial point of view, but at the same time emphasizes that the same processes will result in similar morphology, independent of its host planet. Illustrations show the generalized structure of each major landform type and is complete with a series of special maps published here for the first time. This organized classification of planetary landform types is not available in other books, and only partially covered in scattered papers.The most important places (landforms, named and unnamed) will be found in the main section as well as description and interpretation. This has never been done before. If necessary, these landforms will have an accompanying large-scale map. This will make it serve as a basic reference book - not discussions of large metaconcepts but the stories of well-defined landform types and individual landforms, which is usually only found only in professional papers, one paper, one landform. So this knowledge is very much scattered around in the literature. Each landform will have a data section with height (peaks and low points), diameter, age, data. USGS maps only have diameter data.
How will it be used by planetary scientists? It will give a starting point to any landform he or she want to investigate. Previous works are thematic collections of knowledge (i.e., cratering in the Solar System, volcanic processes, etc.), while this work will approach the subject from landform types and will go deeper by analyzing individual landforms and including maps and imagery. It will be as comprehensive as possible, not only describing the most popular targets but also the (now) lesser known ones, which may be attractive for future analysis.As an example, suppose someone wants to compare valleys of the Moon and Mercury and Titan. He or she can use this work as a starting place to consult and will find imagery, examples, and the basic literature all collected in one section, including individual features, as well as where most valleys are found (global distribution). The maps will be printable and easy to handle, in contrast to large sheet paper maps. As for the content of the maps, they are not global maps but also not very detailed thematic geologic or topographic maps. They fall in between these extremes, which means that the researcher can understand the context but at the same time see all named features. These could serve as perfect reference maps for all planetary bodies. (Such maps are not available online.) The maps will be uniform in many of their cartographic characteristics, which gives the user a good opportunity to compare them, essential in any comparative planetology study (planets, moons, asteroids, etc.). Planetary bodies, where global topographic data is available, will be depicted in both topographic and photomaps and capable of being printed. The maps will contain official IAU names AND also informal geologic (and physiographic province) names that have never been put on maps (except for sketch maps), precisely because they are not official. However, since geologist use these names every day (and often complain about IAU's strict rules), we believe that this make these maps much more useful for workers in the field. Maps are for helping to find places, and these names are very important in this respect. Geologic and physiographic names have never been collected in any form (list or map), not even by USGS Gazetteer, so this will be something brand new. Climatic data (climate diagrams) will be added to maps of Mars. The work will include a full, updated, alphabetical list of names, with links. By 2011, our Russian colleagues may be ready with their corrections of the USGS Gazetteer. If so, the work will include these as well. An Editorial Board will review different sections of the work. Possible Editorial Board Members by region are: WESTERN EUROPE
Ernst Hauber, Institut fur Planetenforschung, DLR, Germany (Mars)
Marita Wahlisch, DLR - German Aerospace Center, Institute of Planetary Research, Germany (Planetary Geodesy, Outer Solar System)
Dennis Reiss, University of Munster, Germany (Mars)
Arnold Gucsik (MPI fur Chemie, Mainz, Germany) (Impact processes) (He is already a Springer book editor)EASTERN EUROPE
Leonid Ksanfomality, Space Research Institute, Moscow, Russia
A. A. Lukashov, Lomonosov University, Moscow (geomorphology)
K. B. Shingareva, MIIGAiK, Moscow (planetary cartography)U.S.
P. Schenk, LPI, USA (planetary morphology and geology)
James R. Zimbelman, National Air and Space Museum, Smithsonian Institution (Earth, Mars, the Moon, and Venus)
Robert Craddock, Smithsonian InstitutionASIA
Hirdy Miyamoto, University of Tokyo, Japan
Huang Q, . Shanghai Astronomical Observatory, Chinese Academy of Science
Dong, S.Y., Faculty of Earth Sciences, China University of Geosciences
Wuhan Oshigami, S., Graduate School of Environmental Studies, Nagoya University
Zhiyong Xiao, China University of Geosciences, Wuhan