Classified information is material that a government body deems to be sensitive information that must be protected. Access is restricted by law or regulation to particular groups of people with the necessary security clearance and need to know, and mishandling of the material can incur criminal penalties. A formal security clearance is required to view or handle classified documents or to access classified data. The clearance process requires a satisfactory background investigation. Documents and other information must be properly marked “by the author” with one of several (hierarchical) levels of sensitivity—e. g. restricted, confidential, secret and top secret. The choice of level is based on an impact assessment; governments have their own criteria, which include how to determine the classification of an information asset, and rules on how to protect information classified at each level. This often includes security clearances for personnel handling the information. Although “classified information” refers to the formal categorization and marking of material by level of sensitivity, it has also developed a sense synonymous with “censored” in US English. A distinction is often made between formal security classification and privacy markings such as “commercial in confidence”. Classifications can be used with additional keywords that give more detailed instructions on how data should be used or protected. 
The need to comprehend and explain our origins--the world of natural phenomena--cannot be properly viewed as exclusively scientific. Instead, it should be viewed as something generally human. Through enchanting, magical narratives involving super-human heroes and heroines, as well as anthropomorphic gods and goddesses, ancient pre-scientific societies attempted to explain and make some order out of the mysterious complexities of the Cosmos. Earth's Moon has always held a place of special fascination for our species, inspiring our human imagination to escape its troubling limitations and--as we search beyond our Earthbound lives--help us to move towards an understanding of who we are, in all our human complexity. Therefore, ancient gods and goddesses mimic our bewitching Moon's unending, gentle tug on the forces of life. In this sense, it may be detrimental to completely dismiss these ancient myths--ascribing them to an unsophisticated and archaic past. Earth's Moon Reveals An Ancient Secret. Many astronomers think that during an ancient era, termed the Late Heavy Bombardment, our young Moon was violently battered by a marauding multitude of invading asteroids that crashed onto its newly formed surface. This attack of pelting objects from space occurred about 4 billion years ago, and the shower of crashing asteroids excavated impact craters, and also slashed open deep fissures, in the lunar crust. This sustained shower of merciless impacts increased lunar porosity, and opened up an intertwining network of large seams under the Moon's surface. As time passed, the region would have cooled down considerably and contracted--thus pulling away from its surroundings and forming fractures akin to the cracks that form in mud as it becomes dry--but on a considerably larger scale.