Astronomy is an interesting profession. Studying stars and planets has to be one of the most fascinating jobs one could ever imagine. One major concern is when it is dark enough to have a good look at those beautiful celestial beings? This will be explained in the article below.
Looking for the quick answer?
The closer to the equator your location, the quicker it takes to get dark after sunset and become what is known as “true darkness.” Across the US, it will take anywhere from 60 to 100 minutes to get dark after sunset. The further north from the equator, the longer true darkness will take to arrive.
How Soon After Sunset Is It Dark Enough For Astronomy?
The time it takes to get dark depends entirely on the location where stars are being observed. In the US, one can see the stars around 70 minutes after sunset, whereas southern states are only able to do so an hour and 40 minutes afterward. The seasons and latitude are also factors to keep in mind, depending on how dark the observer wants the sky to be.
What is Twilight?
Twilight can be defined as the time of the day when the sun is below the horizon, but its light hasn’t abandoned the sky yet. Contrary to popular belief, it can either be before or after sunrise. During Twilight, the sky has a diffused, pink pigmentation due to how the rays are scattered by Earth’s atmosphere. It has three phases, which are determined by how below the horizon is the sun:
- It begins at sunset when the center of the sun goes from 0 degrees of elevation to 6 below the horizon. There’s still enough light to see, but it’s getting dark enough for people to start turning on their lights.
- It comes right after the Civil Twilight, and it often lasts until the center of the sun is 12 degrees below the horizon. It gets fairly dark outside, and the line of a sea horizon stops being visible against the background of the sky.
- This is the last stage of Twilight, where the darkness starts. It begins right after the Nautical Twilight and ends once the sun reaches 18 degrees below the horizon. Afterward, it is officially night, and there’s no sunlight, which makes it perfect for deep space astronomy since all the stars can be seen clearly.
During twilight, sunlight is still visible but the sun is either below the horizon or it hasn’t emerged yet.
Its three stages happen during what is called the blue hour, which is one of the periods of the day, right after the golden hour. These hours are not measured by an exact time, being described as a depiction of the light conditions.
What Can I See During Twilight?
This will depend on which stage anyone decides to look for planets. The position of the sun can showcase or hide things that could be seen in a darker sky. It is recommended to use local conditions as a parameter since it is unknown how far below the horizon the sun is located. The following list will allow determining what can be seen in each phase:
During this stage, only the brightest objects, like Venus and Mercury, are visible. This might be a good chance for astronomers to get a clear shot from them without interferences. Mercury and Venus can be seen in civil twilight because their orbits are between the sun and earth’s orbit.
Photographers can also use the Civil Twilight to their advantage since they will be able to do snapshots without artificial light. The sky tends to be reasonably bright, which is perfect for terrestrial observation images. The light is diffused, and different shades of colors appear, making it an excellent option for portrait and landscape photography. This is also a great opportunity for moon photography, which can be done by using a telescope.
The darkness it provides makes it a good time for stargazing. Cameras can still be used during this time, but pictures might come out very dark and blurry. That doesn’t mean that they can’t be used with a telescope for terrestrial viewing photographs. The latter can pick up larger amounts of light, thus, allowing a perfect snap of a city. During the Nautical Twilight, the sky will turn dark blue, and it will be easy to spot constellations.
During nautical twilight, most stars will be visible. In darker areas, like the sea, a residual background glow is still perceivable. Experts encourage observations of the moon and bright planets. However, deep-sky objects will be partially or wholly invisible in light-polluted areas. On the other hand, urban and city photography is heavily encouraged since the dim and diffused light allows amazing exposure shots.
This period is not the best for normal photographers unless they’re taking pictures of an illuminated city unless they’re dedicated to astrophotography. Depending on whether the area suffers from light pollution or not, bright objects and faint, distant stars can be observed.
Since the sky becomes darker during astronomical twilight, most stars and constellations are visible. It is recommended to carry a telescope since nebulae and galaxies are harder to spot without it. This can also be of great help to observe bright and open clusters, although diffuse objects like galaxies might still be harder to see. The moonlight acts as the sunlight in the astronomical twilight. For photography purposes, it is essential to keep moon phases in mind since they will become the primary source of lighting. However, this stage is perfect for long exposure shots and pictures of planets.
For most of us, there is little to tell the difference between astronomical twilight and night. Except for slight differences in sky brightness at the horizon where you can see what seems like a different shade or light blue hue on one side of the sunset when it’s coming up than before its set down.
The sun has traversed the sky and now places no limit on what you can see, with only one exception: reflections of it off other celestial bodies.
The reverse of these phases is true as we head towards sunrise, starting with astronomical twilight and eventually ending in the sun rising.
What the different stages offer!
The different stages of twilight can be equally productive for photographers since certain colors appear, which can be used for long exposure shots or astrophotography. The gently burning orange color and deep blue illumination can make fantastic scenery. This beautiful phenomenon is due to the scattered sunlight being reflected by particles in the atmosphere, thus, diffusing light.
Despite being only relevant for photographers, the golden and blue hours might be perfect for astronomers to conduct terrestrial exploration. The former is the period that takes up between sunset and the brighter half of civil twilight. During this hour, the sky transitions from red to yellow, creating different nuances of gold. The blue hour, however, coincides with the darker half of civil twilight, making it perfect for terrestrial telescope photography.
Another thing to keep in mind is light pollution. Villages, mountains, and deserts, which are the areas with the lowest levels, generally have identical dawn and dusk. The only difference is the way stars are positioned in the sky. Light polluted areas, however, like cities and areas with industrial pollution, have different looking twilights due to human activity, although they provide unique shots for photographers.
Why is it Not Dark as Soon as the Sun Sets?
The time it takes the darkness to arrive has to do with the Earth’s shape and atmosphere. It is widely known that it is a sphere with a deep atmosphere. Also, the sun is 93 million miles away from Earth; therefore, it continues to shine on the atmosphere above its surface.
The sunlight hits the atmosphere carrying gas molecules like oxygen and nitrogen. As a result, light bounces around and reaches the human eye for a short time after the sunset. This phenomenon is the reason why Twilight has three stages. Thus, the amount of atmosphere that is lit by the sun after sunset keeps shrinking until the astronomical twilight ends.
How Long Does it Take to Get Dark After Sunset?
As it was mentioned earlier, seasons affect the time the light takes to leave the sky. Another factor is the latitude of the observer’s location, but more on that later.
The Impact of Latitude on Time to Darkness After Sunset
The distance from The Equator and distance affect the time it takes to get dark. This is defined as the line drawn around the Earth in the middle between the poles. The Equator divides it into northern and southern hemispheres, which constitutes the parallel of latitude 0. Now, what does this have to do with Twilight? Simple: The distance from the Equator has an impact on when the sun sets, whereas latitude decides how long day and night last and the position of the Sun at noon.
When it comes to seasons, it is well-known that days get shorter during winter and longer during summer, whereas twilights tend to last longer in the former. The December solstice plays a part in this since it’s the time when the Sun reaches the most southerly point in the sky. On the other hand, the Earth’s tilt of 23.5 and its elliptical orbit causes the days to be longer during summer. However, the tilt is not completely constant, which makes the calculations even harder.
Another thing that can make a difference in Sunset time is altitude. Mountains with a bigger elevation have a later sunset because the horizon is lower. Due to the above-mentioned factors, the sunset time can be different in various cities and countries. One curious thing about this is the possibility of a double sunset, which happens in areas with tall mountains. The sun disappears behind a part of the mountain, only to reappear at a different part before sunset.
There is another type of double sunset, which happens when the sun hides behind a tall building. If the sun sets on the ground, it can be easily seen again if an elevator is taken. The difference in time between the two phenomenons is usually 3 minutes.
How Long it Takes to Get Dark After the Sun Sets
This will depend on the location in which the sun is setting. The sunset takes longer to arrive the further the country is from the Equator. Some places don’t seem to experience a real night during summer, whereas it becomes easier to explore the night sky during winter. However, summers are better suited for cameras and photography since the temperature is not too cold to operate the equipment.
The different timezones make it hard to calculate an exact time for the sun to set; therefore, it is recommended to use a specialized website. Research suggests that finding the correct time will help enthusiasts plan accordingly once they decide to either observe stars through a telescope or dedicate themselves to astrophotography.
In our table below, we have compared the time it takes from sunset to get to true night. We have gone with Quito, Ecuador as it’s close to the equator, and moved our way across the US to London, England.
|City||Civil Twilight (Sunset)||Nautical Twilight||Astronomical Twilight||True Night|
|Quito, Ecuador||18:31 – 18:52||18:52 – 19:16||19:16 – 19:41||19:41 – 23:59|
|Key West, Florida||18:24 – 18:47||18:47 – 19:14||19:14 – 19:40||19:40 – 23:59|
|Kansas City, Kansas||18:00 – 18:27||18:27 – 18:58||18:58 – 19:29||19:29 – 23:59|
|Anchorage, Alaska||17:58 – 18:43||18:43 – 19:34||19:34 – 20:24||20:24 – 23:59|
|London, England||17:23 – 17:57||17:57 – 18:36||18:36 – 19:14||19:14 – 23:59|
You can clearly see that it gets darker closer to the equator than in London, England. As you move north away from the equator, you will see it takes longer it takes to get dark.
You can also see that from civil twilight in Quito, Ecuador till true night takes 110 minutes; however, in London, England, the same process takes 191 minutes.
The Impact of Season on Time to Darkness After Sunset
The longer the sun takes to set will depend on the season the country is in. During summer, those who live in the north will experience periods in which there’s no night. Alaska is the perfect example since the sun never moves past the Civil Twilight. The North Pole, however, has 24 hours of daylight in summer.
The sun reaches the most southerly point in the sky during the December solstice. Because of this, the southern hemisphere gets to have the longest days of the year, making it the Summer Solstice. The northern hemisphere, however, has the Summer solstice happen during June.
Contrary to what could be believed of places that don’t experience an actual night, the outside is not bright. Sometimes astronomical twilight doesn’t mean total darkness, despite being the stage in which the sunlight doesn’t illuminate the atmosphere anymore. This means that it is not completely dark, but it allows faint objects that would be hard to spot by a telescope to be detected.
Seasons are inverted between the northern and southern hemispheres. One curious thing about them is the fact that, around the Equator, there are no seasons. Shocking, right? This is because the alignment towards the sun stays constant during the year.
Twilight is the time in which the sun hides below the horizon. There are three stages: Civil, Nautical, and Astronomical, where the light progressively abandons the sky until it’s dark enough to visualize constellations. Latitude, tilt, seasons, and altitude figure among the reasons why the sky tends to darken quicker or slower. What can be seen in twilight depends on the stage the observation is taking place. The different timezones make it hard to calculate how long it will take for the sun to set, so it is essential to consult reliable sources before setting up the tripod and stargazing.