Filament by Ensign February 20, 2021 0 A strand of cool gas suspended over the photosphere by magnetic fields, which appears dark as seen against the disk ...
Finder by Ensign February 20, 2021 0 A small, wide-field telescope attached to a larger telescope. The finder is used to help point the larger telescope to ...
Finderscope by Ensign February 20, 2021 0 A small telescope used to aim your main scope at an object in the sky. Finderscopes have low magnifications, wide ...
Fireball by Ensign February 20, 2021 0 An extremely bright meteor. Also known as bolides, fireballs can be several times brighter than the full Moon. Some can ...
Flare Star by Ensign February 20, 2021 0 A faint red star that appears to change in brightness due to explosions on its surface.
Fluorescence by Ensign February 20, 2021 0 The phenomenon of emitting light upon absorbing radiation of an invisible wavelength.
Focal Length by Ensign February 20, 2021 0 The distance (usually expressed in millimeters) from a mirror or lens to the image that it forms. In most telescopes ...
Focal Ratio (f/number) by Ensign February 20, 2021 0 A lens or mirror's focal length divided by its aperture. For instance, a telescope with an 80-mm-wide lens and a ...
