| Oberon | A moon of Uranus was discovered by William Herschel on January 11, 1787. Oberon is also designated as "Uranus IV". Oberon is the king of the Fairies in William Shakespeare's play A Midsummer Night's Dream. | |
| Objective | The principle optical element of a telescope that collects light and brings it to a focus. | |
| Occultation | Occultation is when a body (usually the Moon) passes in front of (hides) a star or planet. | |
| Octans | The constellation "The Octant" | |
| Off-Axis Guider | An astrophotographic accessory featuring an off-axis prism that intercepts unused light and uses this light to transmit images of guide stars. | |
| Off-Axis Masks | Masks that stop down the aperture of a reflecting or catadioptric telescope. Their apertures are located in an off-axis position to avoid obstruction by the telescope's secondary mirror. | |
| Old Moon | The name of the Full Moon usually in January. Specifically the first Full Moon after Yule (December 22 by "The Maine Rule"). Sometimes known as the "Wolf Moon" or the "Moon After Yule." | |
| Ophelia | A moon of Uranus was discovered by Richard J. Terrile (Voyager 2) on January 20, 1986. Ophelia is also designated as "Uranus VII". Ophelia is the daughter of Polonius in William Shakespeare's play Hamlet. | |
| Ophiuchus | Ophiuchus (The Serpent Bearer) represents Aesculapius, the mythological healer of the sick. Ophiuchus might be considered the 13th Zodiacal Constellation. Over the centuries this constellation has move over the line known as the Ecliptic due to a wobble in Earth's rotation known as 'procession'. (The Ecliptic is the imaginary line that the Sun, Moon and all the planets except Pluto seem to move along. It represents the edge of the solar system.) Originally, the constellations Ophiuchus and Serpens were considered all part of the same 'Snake-Holder' constellation. Located inside Ophiuchus are the following interesting astronomical objects: Bernard's Star, several Messier Objects including (M9, M10, M12, M14, M19, M62, M107) and other open clusters like IC-4665, NGC-6633, also the nebula IC-4603-4604, and The Starfish galaxy (NGC-6240), a double galaxy. | |
Opposition  Opposition |
For planets outside the Earth's orbit (Mars, Jupiter, Saturn, Uranus, Neptune and Pluto), the months around Oppositions are the best time to view these. An Opposition occurs when the planet is opposite from the Sun, relative to the Earth. At Opposition the planet will rise as the Sun sets and will set as the Sun rises providing an entire night of observation. Also at Opposition the planet comes physically closest to the Earth in it's orbit so it appears as large as possible. | |
| Optical Tube Assembly | The telescope part of a telescope system. | |
| Orion | Orion (The Hunter) is one of the best known constellations in the sky, having an hourglass shape and the asterisms of Orion's Belt and Orion's Sword. Located in Orion's sword is one of the brightest nebula, Orion's Nebula (M42), which is a stellar nursery. | |
| Orthoscopic | A eyepiece design invented by Ernst Abbe in 1880. This eyepiece, free of distortion, employs a triplet field lens and a singlet eye lens. It excels in planetary observing. | |
| Orthosie | A moon of Jupiter was discovered by Scott Sheppard and team in 2001. Orthosie is also designated as "Jupiter XXXV" and "S/2001 J9". In Greek mythology, Orthosie was goddess of prosperity. | |
| Oscilloscope | An instrument in which the variations in a fluctuating electrical signal appear as a visible wave on the fluorescent screen of a cathode ray tube. | |
| OTA | Abbreviation for the "Optical Tube Assembly". It is the telescope part of a telescope system. | |
| Oxygen III (O-III) Filter | A type of nebular filter that isolates just the two doubly ionized oxygen lines. | |
| 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. |
