Twilight

Today's the day …………………… to look it up

Twilight [ˈtwʌɪlʌɪt] (noun)
1.  the soft glowing light from the sky when the sun is below the horizon, caused by the reflection of the sun's rays from the atmosphere.
"she looked out on the beautiful twilight"
synonyms: half-light, semi-darkness, dimness, gloom

2.  the period of the evening when twilight is visible, between daylight and darkness.
"a pleasant walk in the woods at twilight"
synonyms: dusk, early evening, evening, close of day, sunset, sundown