An astronomer is a scientist who studies celestial objects and processes, such as stars, planets, galaxies, and the universe as a whole.

Astronomy is a natural science that studies celestial objects, such as stars, planets, comets, and galaxies, as well as the phenomena and processes that occur in outer space.

Cornell University is a private, Ivy League research university located in Ithaca, New York.

Cosmology is the scientific study of the universe as a whole, including its origin, evolution, and ultimate fate.

The Wikipedia page "Expansion of the universe" provides a comprehensive overview of the scientific theory and evidence supporting the idea that the universe is expanding.

A gravitational lens is a phenomenon in astrophysics where the gravitational field of a massive object, such as a galaxy or a cluster of galaxies, bends and distorts the light coming from a more distant object.

Harvard University is a renowned private research university located in Cambridge, Massachusetts, United States.