Why does it not become dark immediately after the sun sets?
Why are Mercury and Venus only visible during the dusk and dawn?
What are the different kinds of twilight and how do they affect astronomy and astrophotography?
Nature photographers need to have an idea on the activities of the sun and onset of the darkness to achieve perfect shots.
For those who want to go stargazing, the perfect clarity and darkness is important to appreciate the vast night sky. Perfect sunsets are also great subjects for photographers. Again, if you want to catch the sky at its best, you need to be aware of the differences and variations of the time in which the sky changes colors. There are a lot of factors that affect it and it has always been a favorite inspiration for folklore, legends, stories, myths, and art.
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If we base it on astronomy, sunset time refers to the time when the upper limb of the Sun disappears below the horizon. When you look at the sunset, the atmospheric refraction in the horizon produces some sort of illusion with the sun’s rays in which we are misled into seeing that the solar disk is one diameter below the horizon.
This is the line between sunset and twilight. So when you know the difference between the two, you can accurately estimate the time when it will be dark enough to appreciate the night sky.
How long until it gets dark after the sun sets?
Depending on the distance from the equator, it usually takes between 20 to 30 minutes for the sky to become dark after sunset. For it to become fully dark, it could take more than an hour and in some places even a little bit longer. It really depends on the location and how far the area is from the Equator.
This time is common for the United States and almost all parts of Europe. Safe to say there is no correct answer to this because it varies on which part of the Earth you are. Also, we need to have a specific context about the term ‘darkness’ – which is very broad – in order to get an accurate answer.
The different types of twilight: day, sunset, to night
Before every sunrise and after every sunset, there are many kinds of darkness that the sky goes through. Different shades from light to dark and vice versa. Twilight refers to the time between day and night when there is still a trace of light from the sun but is slowly fading away, or when it has not fully risen yet. The twilight towards the morning is called dawn and the twilight going into the evening is dusk. They are classified into 3 categories.
In a day, there are two periods of time called the golden hour and the blue hour. These are not characterized by exact times but are determined by a description of the light. We won’t get into much detail about these but we will tackle their significance in the later parts of this article.
The first and brightest twilight happens when the sun is still at less than 6 degrees below the horizon. The moment just before the sun appears in the morning and after the sun has fully set, those are the civil dawn and dusk, respectively.
Astronomers only see the brightest celestial bodies at this time and photographers can take advantage of the civil twilight without using artificial light.
After the civil twilight is a darker form called the nautical twilight when the sun is at an angle between 6 to 12 degrees below the horizon. This is the time when most stars can be seen with the naked eye. This is also the best time for astronomers to view the heavens. At this time, it is already dark and ordinary cameras may not be useful. However, telescopes can capture light so photographers may be able to take shots through it.
When the sun is beyond 12 degrees below the horizon, but not exceeding 18 degrees, that is called the astronomical twilight time. It is in complete darkness and a better time for astronomical viewing. This is not a recommended time for photography due to almost complete absence of light but for astrophotography, which is a special kind, an exception can be made.
The line between actual night and astronomical twilight is hard to determine except through the angle in which the sun is from the horizon. This is the time when distant celestial bodies that take time before the light reaches our atmosphere are visible.
True night time
After all the twilight phases, when the sun has completely set and has no more traces of its light left, that is when it is truly night time. During this time, there is nothing but darkness because we do not receive any light from the sun anymore. Stargazing is best done during these hours.
If we define it scientifically, night time is basically just that span of time wherein the sun is at an angle between 18 and 90 degrees below the horizon. Night time varies on the location relative to the equator and the different seasons as well.
Astrophotography is best done during night time when the only light comes from the heavenly bodies in the sky. At the perfect location, you can get wonderful photos of the Milky Way galaxy, the Northern Lights (Aurora Borealis), and other wonders of the universe.
How long until it gets dark in my region?
The farther up north you are located, the longer the twilight phase lasts in your region during the summer. Several factors come into play with this and it’s hard to accurately describe how it all correlates. Below are the factors that affect twilight time in a particular area:
Latitude and distance from the Equator
As we all know, the Equator is the horizontal line in the middle of the Earth that separates the northern and southern hemispheres. It is the parallel of 0° latitude. Latitude is part of the geographical coordinate related to the north and south parts.
The distance of an area from the Equator determines the length of their day time and night time as well as the sunrise and sunset. However, let’s just clear up that the rise and set of the sun is due to the rotation of the Earth and not the actual activity of the sun.
The latitude determines how long the day and night is in a region. This also affects how long twilight lasts. You can also determine the position of the sun during noon with the latitude. The rule of thumb is that the sun rises earlier and sets later during the March until September Equinox the farther up north you are. During these times, the northern hemisphere is more tilted towards the sun.
Earth’s tilt and the 4 seasons
During the summer, we enjoy longer days and it’s the other way around during the winter. Twilights are also longer in the summer. But it’s not that simple. By December, the sun is near the southern hemisphere. This is why people from the southern parts experience the longest day of the year called the summer solstice but in December. For the northern part of the globe, the summer solstice happens around June.
Since the summer solstice is the longest day of the year, you would think that the sunrise is early and the sunset is late. However, there are some places in the world where this isn’t the case. We can blame this on the combination of the Earth’s orbit and the 23.5 degree tilt.
Whichever part of the earth is tilted towards the sun, you can expect that it is summer time in those regions. However, for the southern hemisphere, the opposite happens. Since the tilt of the earth is not always the same, the time of twilights and seasons are unpredictable. One thing is almost always the same though, the tilt is commonly aligned with the North Star.
Altitudes and double sunsets
Since the altitude largely affects sunset time, the location of the horizon from where you are will define how early or late your sunset will be. That means mountains that are elevated will have a later sunset because the horizon is at a lower level.
A “double sunset” is also possible but rare in areas near very high mountains. This happens when the sun disappears behind one mountain and then reappears behind another mountain before setting completely.
This can also be observed at the Burj Khalifa building where you can watch the sunset from the ground and watch it again at the top. The interval between the second sunset is usually 3 minutes.
Solstice and Equinox
There are two days in a year when the day is just as long as the night. We call this the Equinoxes and they occur whenever the center of the sun is positioned above the equator. This will result in the sun appearing as if it’s above the horizon but it’s actually below it due to the refraction of sunlight.
These Equinoxes usually take place on the 20th day of September when the days are shorter and every 23rd day of March when the days are longer.
The Solstices on the other hand, are the days that are either the shortest (December) or the longest (June). Solstices happen when the Earth is tilted farthest away from the sun and appears to be very high up in the sky.
The bottomline is that it is hard to determine the exact time when twilight begins. One obvious reason is that it has multiple phases. We also have to consider the locations of a specific region relative to latitude, as well as the amount of light pollution, and the seasons. But you do not need to worry because there are websites that can calculate that for you. All you have to do is input the variables.
You also have to keep in mind the severity of light pollution in the area that you want to observe or photograph. In areas without artificial light, those closer to nature, dawn and dusk will look the same and only differ in the placement of the stars. However, for the urban areas with a lot of artificial lights and industrial activity, the twilight will be different. But don’t let that hinder you from taking nice shots.
Both astronomers and photographers have to be aware of the behavior of light as the day goes by. For observational and creative purposes, they can take advantage of the different colors that come up during the different phases of twilight to know when is the best time for observation and photography.
FAQs (Frequently asked questions)
How long before it gets dark in the United States?
The time between the sunset and nightfall is not that long in the US. Depending on what season it is and what state you are in, the duration can be from one to two hours. It will take much longer the farther up north you are.
Deep space objects become visible:
- For southern states: around 70 minutes after sunset
- For northern states: around 100 minutes (1 hour 40 minutes) after sunset
It all varies on the latitude, the season, and the darkness you are referring to.
Why does the sun set in the West?
The earth rotates counterclockwise if the point of reference is the North Pole. Its rotation direction is towards the east. So the sun appears to rise in the east and sets in the west. Even without considering the elliptical orbit of the sun and the tilt of the earth, it will still be the same for the entire planet that the sun rises in the east and sets in the west.
How long does the golden hour last before sunset?
The golden hour occurs at a specific time which is one hour before sunrise and sunset. This is the time when photographers can get a good amount of lighting for their shots.
How long until stars become visible after sunset?
Even if it is not totally nightfall yet, some stars can already be seen as early as a couple of hours after dark. The astronomical twilight stage is already a good time to take out your telescope and gaze at the skies.
Does it get dark before or after sunset?
Night time starts just after astronomical twilight. This is when no light from the sun can reach us and it is already far below the horizon to emit light to a particular part of the earth. When you are stargazing during this time, you can be sure that there is no trace of the sun’s light affecting your view. When the three twilight phases are reversed, that leads to sunrise.
We hope you learned a lot from the information we provided in this article and you gained a better knowledge and awareness about the phenomena that relates to the rising and setting of the sun. Because of the shape of the earth, the time for sunrise, sunset, and twilight is not the same for all due to the many factors that come into play like the latitude, light pollution, and the seasons.