Glossary
The terms MyAstroBoard shows on screen, in plain words, with the page that explains how each one is computed.
| Term | Meaning |
|---|---|
| Airmass | How much atmosphere the light crosses, relative to straight up (1 at the zenith, 2 at 30 degrees of altitude). The higher, the more blur and extinction. SkyTonight’s default limit is 2 (SKYTONIGHT.md). |
| Altitude / azimuth | Height of an object above the horizon (degrees) and its direction along the horizon, from north through east. |
| AstroScore | MyAstroBoard’s 0-to-1 rating of how good a target is tonight from your location: visibility 40%, sky quality 25%, brightness 25%, comfort 10%, plus small bonuses (SKYTONIGHT.md). |
| Astronomical night | The Sun more than 18 degrees below the horizon: the sky is fully dark. The best imaging window is searched inside it (ASTROPHOTOGRAPHY.md). |
| Bortle class | A 1 (pristine) to 9 (inner city) scale of light pollution at your site, set per location (SKYTONIGHT.md). |
| Culmination / transit | The moment an object is highest in the sky, crossing the meridian. |
| Dark window | The part of the night with no Sun and no Moon in the sky. |
| Difficulty | MyAstroBoard’s 0-to-100 estimate of how hard a target is for a beginner, used by “Tonight for you” (BEGINNER_EXPERIENCE.md). |
| DSO | Deep-sky object: galaxy, nebula, star cluster - anything beyond the solar system. |
| Equipment combination | A named set of telescope (or lens), camera, mount and filters that you image with (EQUIPMENT.md). |
| FOV (field of view) | The patch of sky your camera covers through your telescope, in arcminutes (EQUIPMENT.md). |
| Integration time | The total exposure time accumulated on a target, all sub-exposures added (EXPOSURE_CALC.md). |
| Kp index | A 0-to-9 measure of geomagnetic activity; the higher, the further from the poles aurorae can be seen (ASTROPHOTOGRAPHY.md). |
| Magnitude | Brightness on a reversed scale: the smaller the number, the brighter the object. For extended objects, the same light spread over a larger area looks fainter. |
| Meridian flip | On an equatorial mount, the turn the telescope must make when the target crosses the meridian; imaging pauses for a few minutes (PLAN_MY_NIGHT.md). |
| Nautical twilight | The Sun between 6 and 12 degrees below the horizon. SkyTonight runs one hour after nautical dawn and one hour before nautical dusk. |
| Opposition | A planet opposite the Sun in the sky: closest, brightest, visible all night. AstroScore adds a bonus. |
| Seeing | Steadiness of the air, which blurs fine detail; matters most for planets and small targets (WEATHER.md). |
| SQM | Sky Quality Meter reading, in magnitudes per square arcsecond: the darker the sky, the higher the value (about 22 at a dark site) (EXPOSURE_CALC.md). |
| Sub-exposure | One single frame of a series; many are stacked to reach the integration time. |
| Transparency | Clarity of the air (haze, humidity, dust), which dims faint objects (WEATHER.md). |
| TLE | Two-line element set: the orbit data used to predict ISS and CSS passes (SPACEFLIGHT.md). |
Last updated 2026-11-13