Astronomy Dictionary

Browse through Sky at Night Magazine’s comprehensive astronomical dictionary, with over 300 entries.


When the phase (illumination) of a planet or moon’s disc is decreasing in size. For example: ‘A waning crescent Moon can be seen tonight’.

Waxing Moon

Phases of the lunar cycle when the face of the Moon appears to be getting larger each day. In the waning parts of the lunar cycle, the face of the Moon appears to be getting smaller.

White dwarf

A small and dense type of star formed at the end of a star’s life if it has a mass less than the Chandrasekhar limit, which is about 3 x 10^30 kg.

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