Matsyapurana 124.84

124.84

loka ālokane dhātur nirālokastvalokatā
lokālokau tu saṃdhatte yasmātsūryaḥ paribhraman //

The verb (लोक) lôka means to see; alôka (अलोक) is opposite of lôka. The sun in his journey creates this lôka (light) and alôka (darkness); hence this time is called sandhyâ (joining light and darkness), *i.e.*, twilight. Uṣâ is the night and Vyûṣṭi is the day according to the wise.—84-85.