👉 A term used in physics and astronomy, specifically referring to a region of space between two converging lenses. It is often denoted by the symbol "sub-op." This term was first used in the early 20th century by the astronomer Edwin Hubble. It is named for the sub-portion of an image that appears smaller than the entire object but still visible to the naked eye due to the curvature of space, as seen from Earth's orbit around the Sun.
