Having day and night of equal length; occurring around the time of an equinox.
From Latin 'aequus' (equal) + 'diurnus' (daily, from 'dies' meaning day). Related to the equinox, when day and night are equal.
Only two days per year—the spring and autumn equinoxes—are truly equidiurnal on Earth, but some exoplanets might have equidiurnal climates year-round if they don't tilt relative to their stars.
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