How Moon distance determines apparent angular size

Geocentric distance is the center-to-center separation of Earth and Moon at the selected instant. It differs from altitude above Earth's surface and from the distance measured at a user's latitude, longitude, and elevation.

The calculator displays kilometres rounded to a readable whole number. A changed time can change the result even on the same civil date. Time-zone conversion matters because it identifies the instant; equivalent instants expressed in different zones produce the same geocentric range.

Angular diameter follows the ratio between the Moon's physical size and its distance. The geometry uses an arctangent relationship because kilometres and arcminutes do not change linearly at every scale. The result is expressed in arcminutes because the lunar disc spans roughly half a degree in the sky.

Angular diameter describes geometric sky span. Perceived size near a horizon, photographic pixels, and visibility also depend on camera settings, cropping, display scale, terrain, atmosphere, and perception.