| Facula | A calcium cloud in the Sun's chromosphere, seen in projection against the photosphere in white light and detectable most easily near the Solar limb. | |
| Ferdinand | The outermost moon of Uranus was discovered by Matthew J. Holman, John J. Kavelaars, Dan Milisavljevic, and Brett J. Gladman on August 13, 2001. Ferdinand is also designated as "Uranus XX!V" and "S/2001 U2". Ferdinand is the son of the King of Naples in William Shakespeare's play The Tempest. | |
| Field Curvature | Curvature of a telescope's focal surface inherent in certain telescope designs. In this aberration, the image does not fall on a flat plane. Thus, the focus changes from the center to the edge of the field of view. As the image is viewed, it appears sharp and crisp either at the center or at the edges of the field of view but not both. | |
| Filaments | A solar prominence seen in projection against the Sun's photosphere. | |
| Filar Micrometer | An eyepiece which has threads across the field of view for more accurate measurement. | |
| Finder Telescope | A small auxiliary wide-field telescope used to locate objects for viewing through a larger telescope to which it is attached. | |
First Quarter Moon  First Quarter Moon |
For the week between the New Moon and the First Quarter Moon the sunlit side of the Moon grows as a waxing (growing) crescent until the disk of the Moon is half lit. This half lit point is known as the First Quarter Moon. After the First Quarter the sunlit part of the Lunar disk is called waxing gibbous as it grows to illuminate the full disk of the Moon. | |
| Flares | A brief, sudden brightening in the sun's atmosphere that accompanies a burst of radiation from a sunspot. | |
| Flower Moon | The name of the Full Moon usually in May. Specifically the second Full Moon after Ecclesiastical Vernal Equinox (March 21). Sometimes called the "Milk Moon" or the "Corn Planting Moon." | |
| Focal Length | The effective distance from a telescope objective to the focal plane. This distance is not apparent in compound telescopes. | |
| Focal Plane | Plane at the focal length of a lens or concave mirror on which an object is focused. | |
| Focal Ratio | The ratio of a telescope's effective focal length to its aperture. | |
| Focus | Place at the focal length where light rays from an object are converged by a lens or concave mirror. | |
| Focusing Mirror | A Primary Mirror which is moved to focus a catadioptric optical system. | |
| Fornax | The constellation "The Furnace" | |
| Francisco | A moon of Uranus was discovered by Matthew J. Holman, John J. Kavelaars, Dan Milisavljevic, and Brett J. Gladman on August 13, 2001. Francisco is also designated as "Uranus XXII" and "S/2001 U3". Francisco is a lord in William Shakespeare's play The Tempest. | |
| Frequency | Number of waves that cross a given point per unit time, or the number of vibrations which occur per unit time. | |
| Frosty Moon | The name of the Full Moon usually in November, if the November Full Moon is not the Hunters Moon. Specifically the second Full Moon before the Autumnal Equinox (September 23 by "The Maine Rule"). Sometimes known as the "Beaver Moon." | |
| Fruit Moon | The name of the Full Moon usually in September, if the September Full Moon is not the Harvest Moon. Specifically the first Full Moon before the Autumnal Equinox (September 23 by "The Maine Rule"). Sometime known as the "Corn Moon" or "Barley Moon." | |
Full Moon  Full Moon |
A Full Moon appears when the side on the moon facing Earth is completely sunlit. At this point the Moon is at Opposition to the Sun: rising as the Sun sets and setting as the Sun rises. If the Earth actually passes between the Sun and the Moon so that it's shadow passes across the Lunar surface that event would be a Lunar Eclipse. The Full Moon is typically the worse time for deep sky observing because the "moon glow" affects the dark sky. | |
| The "Stars and Scopes" Glossary was compiled by Peter Ue from various sources on the internet. I tried to correct and edit as much as possible, but I can make no claim or warrenty to the information here. If you find any errors just contact me and I'll try to fix it - Thanks , Peter. |
