What you need to know about the time switch
How early will it get dark after we switch back to standard time on Nov. 4? The easy answer is an hour earlier than it did the night before. But for those of us who don’t keep close tabs on nightfall (or daybreak), here’s a quick description of the stages of twilight and when they’ll occur in the Bay Area during the first days of standard time.
(If you’re not in the Bay Area, the stages of twilight will still match the descriptions, but you’ll need to check an astronomical table — such as those at timeanddate.com — to get the right times for your location.)
The three stages of twilight, each about half an hour long, are delineated by the angle of the sun in relation to the horizon. Morning twilight ends at sunrise, evening twilight begins at sunset.
The darkest of the twilights is astronomical; to an astronomer, it’s not the same as night, but to the layman
it’s close enough. Nautical twilight is a deep dusk — dim bluish sky, bright planets visible. In civil twilight, the sky is light all over though the sun is not visible.
Following are some observations of those stages, with an eye toward how they look to pedestrians and cyclists.
MORNING
Nautical twilight, morning: Half an hour in which it goes from dark to some lightening of the sky and pale or reddish at the eastern edge. Trees and buildings can be seen sharply against the sky, but it’s still very dim on the ground — it would be easy to step into a hole, and pedestrians would probably want a flashlight or headlamp. Bicyclists on the street definitely would want the full complement of lights. (Nov. 4, 5:38 to 6:09 a.m.)
Civil twilight, morning: Half an hour in which the sky lightens all over. At the start of civil twilight, the sky is light blue and colors of objects are easier to detect. By the midpoint, you can read a newspaper outside under open sky. Pedestrians no longer need a light but would probably want reflectors or bright clothing if they’re near traffic, especially on an overcast day. (Nov. 4, 6:09 to 6:36 a.m.)
Technically, the end of civil twilight coincides with sunrise. In much of the Bay Area, though, the sun is not visible until about 10 minutes after official sunrise time, because of the hills to the east. (Nov. 4, 6:36 a.m.)
EVENING
In much of the Bay Area, the sun disappears behind the western hills 10 minutes or more before official sunset time, which on Nov. 4 is 5:07 p.m.
Civil twilight, evening: Reverse of the morning progression. Sky starts out pale but dusky, often pinkish. Streetlights come on. Good visibility for exercising outside, but you wouldn’t want to be wearing dark glasses, and toward the end of the half-hour you’d want reflectors if you’re near vehicle traffic. (Nov. 4, 5:07 to 5:34 p.m.)
Nautical twilight, evening: Reverse of the morning progression. The brightest planets become visible, all but the most vibrant colors are muted to shades of gray. Trail running is dicey without a headlamp, particularly if you’re in the trees. By the end of nautical twilight, it is night for most purposes. (Nov. 4, 5:34 to 6:05 p.m.)
Through Dec. 21, the days will get shorter. Daylight duration decreases about two minutes a day in early November; by the time we get to the winter solstice, we’re losing only a few seconds of daylight each day. On the shortest day of the year, sunrise will be at 7:19 a.m. and sunset at 4:54 p.m.