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The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-earth object (NEO). It combines two types of data—probability of impact, and estimated kinetic yield—into a single "hazard" value. A rating of 0 means the hazard is equivalent to the background hazard (defined as the average risk posed by objects of the same size or larger over the years until the date of the potential impact).〔 A rating of +2 would indicate the hazard is 100 times greater than a random background event. Scale values less than −2 reflect events for which there are no likely consequences, while Palermo Scale values between −2 and 0 indicate situations that merit careful monitoring. A similar but less complex scale is the Torino Scale, which is used for simpler descriptions in the non-scientific media. ==Scale== The scale compares the likelihood of the detected potential impact with the average risk posed by objects of the same size or larger over the years until the date of the potential impact. This average risk from random impacts is known as the background risk. The Palermo Scale value, ''P'', is defined by the equation: : where : *''pi'' is the impact probability : *''T'' is the time interval over which pi is considered : *''fB'' is the background impact frequency The background impact frequency is defined for this purpose as: : where the energy threshold E is measured in megatons, yr is the unit of T divided by one year. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Palermo Technical Impact Hazard Scale」の詳細全文を読む スポンサード リンク
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