The following image compares a detail from Rükl's Atlas (Sheet 22, right) with the comparable area as seen in the newer Lunar Orbiter-based IAU/USGS on-line Digital Atlas ( Sheet 41, left, much reduced):.The current authorized edition of Rükl's Atlas of the Moon is said to be available from Sky Publishing, although it is reportedly out-of-stock. Reproductions of Rükl's maps can be found on a number of websites.Rükl's maps do not show all IAU-approved satellite feature names (at the time the maps were being prepared, the IAU did not maintain an official list of lettered craters), and in a very few cases his labels are erroneous or ambiguous. In recent years, printed maps of this sort have been somewhat supplanted by electronic products which are generally more flexible, and can be more easily updated to reflect changes in the official nomenclature and avoid inadvertent errors. Rükl uses the traditional system of labeling satellite features by their letters only, placed on the side towards the parent feature after which it is named.Although this is a private publication, Rükl has generally striven to adhere to the IAU nomenclature as closely as possible. In the image below, impact melt flowed downhill and pooled, where it cooled.Description This series of careful maps of the Moon's nearside and libration zones, created by the former director of the Prague Planetarium, is widely regarded by amateur astronomers as the indispensable observing guide to lunar features. The floor of the crater is covered in impact melt, rocks that were heated to such high temperatures during the impact event that they turned to liquid, and flowed across the floor. Tycho's central peak is thought to be material that has rebounded back up after being compressed in the impact, and though it's a peak now, it originated at greater depth than any other portion of the crater. Tycho is also of great scientific interest because it is so well preserved, it is a great place to study the mechanics of how an impact crater forms. The problem is, there aren't that many places for which we've sampled the rocks, and confirming the age of Tycho would help date younger surfaces, which are not well sampled. ![]() Planetary surfaces are dated by counting the number of craters on the surface, and comparing that number to the number of craters that formed on a surface for which we know the age by actually sampling the rocks. Directly sampling material from within the crater would help us learn more about not just when Tycho formed, but the ages of terrains on other planets throughout the solar system. This may still seem old, but compared to the 3.9 billion-year age for many large lunar craters, Tycho is the new kid on the block. So if these samples are truly from Tycho, the crater formed 108 million years ago as well. These samples are impact melt glass, and radiometric age dating tells us that they formed 108 million years ago. How old is Tycho? Because the impact event scattered material to such great distances, it's thought that some of the samples at the Apollo 17 landing site originated at the Tycho impact site. All craters start out looking like this after they form, but their rays gradually fade away as they sit on the surface, exposed to the space environment which over time darkens them until they fade into the background. It formed recently enough that its beautiful rays, material ejected during the impact event, are still visible as bright streaks. What really makes Tycho stand out is its relative youth. At 53 miles (85 kilometers) in diameter, it is just one among thousands similary-sized craters. Tycho's prominence is not due to its size. It appears as a bright spot in the southern highlands with rays of bright material that stretch across much of the nearside. Tycho Crater is one of the most prominent craters on the Moon.
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