Altitude
The angle above the local horizon. A negative altitude is below the horizon.
WORDS THAT OPEN WORLDS
Astronomy, in plain language.
A compact reference for the terms you’ll meet throughout the observatory.
Aperture
The diameter of the light-gathering opening of an optical instrument.
Astronomical twilight
The interval when the Sun is between 12° and 18° below the horizon.
Azimuth
The compass direction of an object, measured from north through east: north 0°, east 90°.
Declination
A celestial latitude-like coordinate north or south of the celestial equator.
Light-year
The distance light travels in vacuum in one Julian year; a unit of distance, not time.
Magnitude
A logarithmic brightness scale. Smaller numbers mean brighter objects.
Redshift
A shift of spectral features toward longer wavelengths. It has several physical causes.
Right ascension
A celestial longitude-like coordinate measured in hours. One hour corresponds to 15°.
Seeing
Atmospheric turbulence that blurs or makes astronomical images shimmer. Cloud cover is not a seeing measurement.