Glossary term: 달
Description: 달은 스스로 빛을 내는 천체가 아니라 달에 햇빛을 반사하는 천체입니다. 이 때문에 달의 특징적인 위상이 만들어집니다. 달은 지구의 유일한 주요 자연 위성이며, 크기와 질량 면에서 태양계 자연 위성 중 다섯 번째에 해당합니다. "달"은 태양계 및 그 밖의 다른 자연 위성 또는 달과 구별하기 위해 대문자로 표기되었습니다. 다른 태양계 위성과 비교할 때 달은 공전하는 행성의 크기에 비해 가장 큰 크기를 가지고 있습니다. 달은 지구와의 평균 거리가 384,000킬로미터(km)인 지구 주위를 타원형 궤도를 따라 공전합니다. 달에는 대기가 없으며 철이 풍부한 핵과 암석으로 이루어진 외층 등 지구와 비슷한 물질로 구성되어 있습니다. 이러한 유사성은 우연이 아닙니다: 우리가 아는 한 달은 약 45억 년 전 지구와 화성 크기의 행성이 충돌한 잔해로 형성되었으며, 대부분의 물질은 원래 지구의 맨틀에서 유래했습니다. 달의 표면에는 바다로 알려진 어두운 지역과 밝은 고지대가 있으며, 크레이터가 곳곳에 자리 잡고 있습니다. 달의 표면적은 3.79 x 107 제곱킬로미터, 부피는 2.20 x 1010 입방킬로미터, 질량은 7.35 x 1022 킬로그램(kg)입니다. 지구 주위를 도는 달의 공전 주기의 정확한 값은 기준 프레임에 따라 달라지는데, 먼 별을 기준으로 하면 27.3일마다 한 번씩 공전을 완료합니다("항성 주기"). 지구에 있는 관측자의 경우, 두 개의 초승달 사이의 시간은 29.5일("공전주기")입니다.
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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