In grammar, this is a part of speech. There are two articles in English: the definite article the and the indefinite article a or an. The definite article identifies a particular noun: the book I need and the indefinite article indicates an unidentified noun: bring me a book. The indefinite article an is used in front of a vowel: an owl.
The disc represents the full moon, traditionally the most auspicious time for work and celebration. The disc is set towards the hoist. Effective date: 1 January 1981.