When I first began to work on this website, I tried very hard to minimize the use of technical terms. That turned out to be impossible. Amateur astronomy may be a hobby, but it is also highly technical and it is much easier to talk about things if one can use a minimal technical vocabulary. I will work hard not to get carried away and I will keep definitions as simple as possible, but we are going to need some use of technical terms. If I use a technical term which is not defined here, drop me an email and I will be sure to include it.
APPARITION: The interval during which any one of the superior planets can be viewed in the night sky. For example, the apparition containing the 2017 opposition of Jupiter began in early October of 2016 when the rising of Jupiter just before dawn made the planet briefly visible prior to the rising of the sun. Jupiter rose earlier each day from that point until, on the day of opposition 07 April, 2017, it was visible from sunset until dawn. Since the planet continued to rise earlier each day, it eventually set at sunset in early September of 2017. Although the apparition lasted ~11 months, optimum viewing opportunities for Jupiter were ~ +/- 3 months centered at opposition.
EXPOSURE: The length of time required to expose each frame of an image video. The value is in milliseconds (mS) and, since each second contains 1,000 mS, it is easy to convert to the more familiar fractional values used in film photography. Short exposures are desirable to obtain the sharpest individual images, but exposures are dependent on light intensity, so dimmer planets (like Saturn) require longer exposures (like it or not!).
ELEVATION: (Elev.) The elevation of the object (in degrees). High elevations (40-60 deg.) are desirable as the telescope is imaging through less atmosphere, which should result in sharper image frames. An elevation of 20 deg. or less is very undesirable as atmospheric distortion is almost assured. What happens between these two extremes is entirely a result of the seeing in effect at the time.
FOV: Field of View of any optical system
GAIN: The gain setting of the video camera (usually a percentage of 100%). Increased gain can shorten exposure, but unless the camera has a very low-noise video amplifier, setting the gain too high can result in noise that is difficult to temove without comp;romising the image.
OPPOSITION: The time marked by the alignment of the Sun, the Earth, and any one of the superior planets. If planetary orbits were all circular, opposition would also mark the point of closest approach of the Earth and the particular planet. Given the elliptical nature of real-life orbits, the time of closest approach typically falls within a view days of the geometric opposition. There is nothing sacred about the precise date of an opposition as excellent imaging can be realized within a month, either side of opposition, and there is an even wider “window” for larger planets like Jupiter. The time interval between oppositions is 2 years and 50 days for Mars, 1 year and 34 days for Jupiter, and 1 year and 14 days for Saturn.
PRIME FOCUS: Images obtained at the native focal ratio of the telescope without the uses of Barlow or PowerMate lens system that increase the effective focal length and ratio, thus increasing image scale.
RAW image format:
RGB24 image format:
SEEING: The result of the various distortions in the atmosphere that will always degrade image quality to some extent. Seeing is said to be poor when there is a lot of atmospheric distortion and good to excellent when distortion is minimal. If the elevation of a planet is quite low, seeing will typically be worse then what would be seen if the planet was higher in the sky since in the latter case there is less atmosphere between the observer and the target.
SUPERIOR planet: A planet located farther from the Sun than the Earth (Mars, Jupiter, Saturn, Uranus, and Neptune).
UTC: Coordinated Universal Time – essentially equivalent to Greenwich Mean Time (or GMT), the time at the prime meridian.