Do you love twilight? Learn about the 3 stages

Twilight is that magical time of day when a glow still pervades the air even though the sun has set. It happens twice a day, before sunrise and after sunset. Earth’s atmosphere scatters the sun’s rays to create the colors of twilight. On worlds with no atmospheres, such as the moon, the sky falls instantly dark after the sun sets.

And, if you could see twilight from outer space, you’d find that it isn’t marked by a sharp boundary on Earth’s surface. Instead, the shadow line on Earth – sometimes called the terminator line – is spread over a fairly wide area on the surface and shows the gradual transition to darkness we all experience as night falls.

Part view of Earth from orbit showing fading colors from light side to dark side.
Twilight on Earth, viewed from space. Astronauts aboard the International Space Station captured this photo – a single digital frame – in June 2001. On the right, you see Earth illuminated by the sun. On the left, it’s nighttime. Between, washed in subtle colors, is the realm of twilight. Image via ISS Expedition 2 Crew/ Gateway to Astronaut Photography of Earth/ NASA.

3 types of twilight

Astronomers recognize three different stages of twilight: civil, nautical and astronomical. All three stages happen twice in a 24-hour period, between day and night and then repeating in reverse order between night and day.

Diagram with 3 wedge-shaped areas, from light to dark blue, labeled with twilight types.
The 3 types of twilight. Image via TWCarlson/ Wikimedia Commons/ (CC BY-SA 4.0).

Stage 1: Civil twilight

Let’s consider the stages of twilight as occurring after sunset. Keep in mind that they would reverse their order at sunrise. Civil twilight begins the moment the sun slips below the horizon. The official definition of civil twilight is the time from when the sun disappears until the sun’s center is 6 degrees below the horizon. A measurement of 6 degrees of sky is a bit more than three fingers held at arm’s length.

During civil twilight, there’s enough light to see, but people turn on their lights to drive a car, and the streetlights are starting to come on. The brightest planets appear during civil twilight.

For mid latitudes, civil twilight lasts a bit longer in summer and winter and is a bit shorter in spring and fall. In spring and fall, the sun rises and sets more directly in the east and west. Therefore, it makes a straighter path downward (or upward), reaching the 6 degree mark in a shorter period of time. In summer and winter, the sun arcs across the sky, cutting across the horizon at an angle. This angle is more pronounced in summer, which is why civil twilight lasts the longest in summer. Civil twilight in mid latitudes can last, on average, 1/2 hour.

Compare this to tropical regions. At the equator, the length of civil twilight hardly varies. The sun around the equator makes a path across the sky that cuts cleanly down toward the horizon at sunset in a nearly perpendicular fashion. Therefore, the sun and its rays disappear faster, giving equatorial regions a shorter twilight than higher latitudes. Near the poles, twilight times last much longer.

Stage 2: Nautical twilight

In the evening, nautical twilight takes over where civil twilight ends. The definition of nautical twilight is the time period when the center of the sun is 6 degrees below the horizon to 12 degrees below the horizon. You can remember the name “nautical” because it ends when the distant line between sea and sky is no longer distinguishable. Also, more bright stars appear during this time, which was important in the early days of navigation. When nautical twilight began, sailors could use the stars as directional cues.

During nautical twilight, terrestrial objects are visible, but you need artificial lights to carry on outdoor activities.

For polar regions, the summer sun does not get more than 12 degrees below the horizon. Therefore, these regions have nautical twilight all night long, never reaching astronomical twilight or total darkness. For mid latitudes, nautical twilight can last from about 1/2 hour in spring, winter and fall, to about 45 minutes in summer.

Stage 3: Astronomical twilight

The darkest twilight stage is astronomical twilight. The definition of astronomical twilight is the period of time when the center of the sun is 12 degrees below the horizon to 18 degrees below the horizon. You probably don’t even notice any illumination left in the sky at this time.

For stargazers, this is the time when fainter stars, clusters and other sky objects appear and become good observing targets.

In mid latitudes, astronomical twilight can last about 1/2 hour from fall through spring but up to an hour in summer. Astronomical twilight begins about an hour to 1 1/2 hours after sunset for mid latitudes. So, as a rule of thumb, if you’d like to observe something in the night sky that isn’t particularly bright, you should wait about 90 minutes after sunset before you start observing.

Photo gallery from the EarthSky community

Bright yellow sunset sky fading to partly-cloudy orange above, with dark buildings and trees in foreground.
View at EarthSky Community Photos. | Pat Fogg in Claresholm, Alberta, Canada, captured this image of early twilight on June 23, 2023. Pat wrote: “Sunset looking west to the Porcupine Hills.” Thank you, Pat!
Venus and Jupiter in purple twilight sky, in a tropical setting, above an ocean.
View at EarthSky Community Photos. | Stephen Humphrey in Punta Mala, Costa Rica, shared this image of the sky’s 2 brightest planets – Venus and Jupiter – from February 8, 2023. Thanks, Stephen!
Colorful sunset sky with comet-like rocket exhaust leading down over horizon, and one bright planet.
View at EarthSky Community Photos. | Peter Forister in Gordonsville, Virginia, took this image on September 24, 2022. Peter wrote: “Spectacular sunset colors with the SpaceX Starlink rocket launch this evening. Sunset light illuminated the exhaust gases from the Falcon 9 rocket as it launched, creating the ‘twilight phenomenon’ show up the East Coast.” Thank you, Peter!

Bottom line: Twilight is that magical time between sunlight and darkness. Astronomers, the experts on nighttime, recognize three stages of twilight.

August 27, 2023

Like what you read?
Subscribe and receive daily news delivered to your inbox.

Your email address will only be used for EarthSky content. Privacy Policy
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

More from 

Editors of EarthSky

View All