毕业为什么要穿学士服呢？

In the often unheated buildings of the middle ages, long gowns were necessary for scholars to ward off the cold.
       在中世纪，房屋里一般不具备取暖设备，长袍成为了学子们避寒的必需品。
        Academic dress for graduations started in the 12th and 13th centuries when universities first began forming. Whether a student or a teacher, standard dress for scholars was clerical garb. Most medieval scholars had made certain vows, and had at least taken minor orders with the church so clerical robes were their main form of dress to begin with.     
        毕业生穿着的学位服起源于大学形成初期的12至13世纪。当时无论学生还是老师，学者的标准服饰是牧师的衣装。大多数中世纪学者都要进行某种宣誓，并且起码举行一些宗教仪式，所以牧师的长袍成为早期学位服的主要形式。

  In 1321, the University of Coimbra mandated that all Doctors, Bachelors, and Licentiates must wear gowns. In the latter half of the 14th century, excess in apparel was forbidden in some colleges and prescribed wearing a long gown. By the time of England's Henry VIII, Oxford and Cambridge began using a standard form of academic dress, which was controlled to the tiniest detail by the university.
         在1321年，孔伯拉大学要求所有的博士、学士和硕士必须穿长袍。在随后的14世纪中叶，一些学院禁止过度花哨的服装，并且规定穿长袍。在英国亨利八世时期，牛津和剑桥大学开始采用一种标准款式的学位服，这是大学做出的最细微的规定。
       Not until the late 1800s were colors assigned to signify certain areas of study, but they were only standardized in the United States. European institutions have always had diversity in their academic dress, but American institutions employ a definite system of dress thanks to Gardner Cotrell Leonard from Albany, New York. After designing gowns for his 1887 class at Williams College, he took an interest in the subject and published an article on academic dress in 1893. Soon after he was asked to work with an Intercollegiate Commission to form a system of academic apparel.
        直到1800年，颜色才被用到学位服上预示着某一类学科，但是他们在美国是整齐划一的。欧洲的大学经常有不同种类的学位服，拜纽约奥尔巴尼的加德纳·科特尔·伦纳德所赐，美国的大学采用了一套规格确定的学位服。在为1887年的毕业班设计出长袍学位服后，他对这一领域产生了兴趣并且于1893年发表了一篇关于学位服的文章。不久，他被任命到校际委员会来规划一套学位服。
      The system Gardner Cotrell Leonard helped form was based on gown cut, style and fabric; as well as designated colors to represent fields of study. For example green was the color of medieval herbs, and was assigned to medical studies. Because olive is close to green, was designated for pharmaceutical studies.
         加德纳·科特尔·伦纳德设计形成的学位服系统建立在长袍的裁剪、款式和面料上，同时指定不同颜色代表某一学科。比如绿色是中草药的颜色，于是绿色就被运用到医学上。因为橄榄接近绿色，橄榄色就被运用到药学上。

I thought you are in china~