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For other uses, see Air gun (disambiguation). An air gun (or airgun ) is any kind of gun that launches projectiles pneumatically with compressed air or other gases that are pressurized mechanically without involving any chemical reactions, in contrast to a firearm, which pressurizes gases chemically via an exothermic oxidation (deflagration) of combustible propellants which generates propulsive energy by breaking molecular bonds. Both the long gun and handgun forms ( air rifle and air pistol ) typically propel metallic projectiles, that are either diabolo-shaped pellets, or spherical shots called BBs. Certain types of air guns (usually rifles) may also propel darts or arrows. The first air guns were developed as early as the 1500s. They have been used in hunting, sporting and warfare. Modern air guns use one of three types of power source depending on the design: spring-piston, pneumatic, and bottled compressed gas (most commonly carbon dioxide). Contents 1 Hist

赫尔贝里环形山 月球轨道器4号拍摄的位于晨昏圈上的赫尔贝里环形山 纬度 22.63°N 经度 102.46°W 直径 61.93公里 深度 2.72公里 月面座標 日出时103° 命名来源 罗伯特·杰·赫尔贝里 赫尔贝里环形山 （Helberg）是位于月球背面北半部一座古老的大撞击坑，约形成于39.2-38.5亿年前的酒海纪 [1] ，其名称取自美国航天航空工程师"罗伯特·杰·赫尔贝里"(Robert J. Helberg，1906年-1967年)，1970年被国际天文学联合会正式批准接受。 目录 1 描述 2 卫星陨石坑 3 参引资料 4 另请参阅 5 外部链接 描述 该陨坑西侧几乎与罗伯逊环形山相接壤、西北毗邻伯克纳环形山，往东面更远处则坐落着贝尔环形山 [2] 。该陨坑中心月面坐标为 22°38′N 102°28′W  /  22.63°N 102.46°W  / 22.63; -102.46 ，直径61.93公里 [3] ，深度约2.72公里 [1] 。 赫尔贝里环形山是一座已受侵蚀的撞击坑，它东北偏北部分坐落在卫星坑"赫尔贝里 C"的坑壁上，而东南侧则被卫星坑"赫尔贝里 H"覆盖，南侧边缘有些不规则，西南部略微向外突出。它的坑壁最大高出周边地形1220米 [1] ，内部容积约3280公里 3 [1] 。坑内靠近北侧内壁坐落一座残迹坑，除此外，没有其它较醒目的地貌结构。 赫尔贝里环形山所在区域有时在月球摄动期间会进入，因此，在照明条件较好时可观察它，但即使在种的情况下也只能看到其侧面，更多的细节无法看清。 卫星陨石坑 按惯例，最靠近赫尔贝里环形山的卫星坑将在月图上以字母标注在它的中心点旁边. 卫星坑图， 月球勘测轨道飞行器拍摄。 赫尔贝里 纬度 经度 直径 C 23.4° N 100.6° W 70 公里 H 21.8° N 101.2° W 29 公里 参引资料 ^ 1.0 1.1 1.2 1.3 Lunar Impact Crater

For other uses, see Bicycle (disambiguation). "Bike" redirects here. For other uses, see Bike (disambiguation). The most popular bicycle model—and most popular vehicle of any kind in the world—is the Chinese Flying Pigeon, with about 500 million produced. [1] Classic bell of a bicycle A bicycle , also called a cycle or bike , is a human-powered or motor-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A bicycle rider is called a cyclist, or bicyclist. Bicycles were introduced in the late 19th century in Europe, and by the early 21st century, more than 1 billion were in existence at a given time. [1] [2] [3] These numbers far exceed the number of cars, both in total and ranked by the number of individual models produced. [4] [5] [6] They are the principal means of transportation in many regions. They also provide a popular form of recreation, and have been adapted for use as children's toys, g