• The two stars rotate in elliptical orbits about a common centre of gravity.
• The Moon orbits ( or circles ) the Earth.
• The two stars rotate in elliptical orbits about a common centre of gravity.
• The Moon orbits ( or circles ) the Earth.
Циммерман М., Веденеева К.. Русско-Английский научно-технический словарь переводчика. Russian-English scientific dictionary for translators. 2012