While the 20th is the longest day of the year, this week is the earliest sunrise at 4:42 AM. I ride to work from 3:20 - 3:45, arriving in the time of day called Nautical Twilight, just before Civil Dawn the start of Civil Twilight. I took a picture this morning to show what the sky looks like as I am locking up my bike at 3:45 AM. At 3:55 AM, the phase of twilight changes from Nautical Twilight to Civil Twilight. From TimeAndDate.com: "Twilight is the time between day and night when the Sun is below the horizon but its rays still light up the sky. Astronomers differentiate between 3 phases: Civil twilight; Nautical twilight and Astronomical twilight. Each twilight phase is defined by the solar elevation angle, which is the position of the Sun in relation to the horizon. During nautical twilight, the geometric center of the Sun's disk is between 6 and 12 degrees below the horizon. In clear weather conditions, the horizon is faintly visible during this twilight phase. Many of the brighter stars can also be seen, making it possible to use the position of the stars in relation to the horizon to navigate at sea. This is why it is called nautical twilight. Civil twilight is the brightest of the 3 twilight phases. The Sun is just below the horizon, so there is generally enough natural light to carry out most outdoor activities."