In this article I'll be diving into the world of chronolocation, metadata and shadows. Since this is the largest article I've written so far, I've decided to create a table of contents for your convenience. At the end of every chapter and after long paragraphs, there's a link to bring you back there if you need it. Since I know there will be updates in the future, I also added a document version control, for an easy overview of the changes.
I have always been intrigued by the way forensic examiners were able to determine a timestamp for photos or events, without having direct knowledge of it in the first place. Since I became a regular member of the Quiztime community, having done quite a bit of 'geolocation' during those quizzes and some more serious investigations, and more than once there wasn't just the question of where a certain photo or video is shot, but also when it happened. In this guide, I am going to dive a little deeper into the techniques of what is called ‘chronolocation', the act of determining or estimating a time or time frame of an event or situation that was captured by visual media.
This article has been in the making for a very long time! It basically started during February 2018 when I was able to determine the possible date and time of a photograph that was posted as one of the daily verification quizzes by the Twitter account Quiztime. Later that same year I spent some evenings on determining the possible date of an extrajudicial execution in Cameroon. After this people started contacting me with questions about the techniques I used, or requests to help in investigations. And so, we end up in early 2019, when I started to write this lengthy tutorial. But due to all kinds of other commitments I've never been able to finish this, until now.
The writing of it has been quite a journey I must say! It took me weeks to even get an overview of subjects I wanted to touch. Then multiple weeks of writing things on my personal blog on Medium, followed by transferring it all to a separate document, since it was getting way too big. I planned to release it as a PDF on GitHub, but after I decided to host my own blog things finally took off again. And I finally took the time to transfer everything to here and finally was able to finish it.
And when I saw that others, like Nick Waters, were posting little write-ups as well about it, it was time to get to work again. After more endless nights and weeks of working on it in my spare time, I somehow actually was able to finish something I felt comfortable sharing with the world. So here it is… A guide that is probably nowhere near being complete! But as far as I was able to find it is one of the first and maybe the only one of its kind at the moment.
When it comes to establishing a time frame, it turns out that both the art of geolocation and chronolocation have similarities. The main difference is that a global indication of the location is needed for chronolocation if we want to be precise. But both techniques demand a thorough investigation of every part of a photo or video, an understanding of the surrounding area, some local knowledge and maybe even the weather. Where for geolocation the knowledge is used to find a possible location, in chronolocation we use that information to narrow down the possible time frame.
Besides that, both geolocation and chronolocation can complement each other. Where the knowledge of a precise location can help determine an accurate time frame, a shadow can aid an investigator in geolocation by giving a clue in which direction a photo or video was shot. But it can also be important to determine a time or date to find specific events that happened around that moment in time, to zoom in on possible locations.
The goal of this guide is to give a basic understanding of chronolocation and to share it with everybody who needs to apply the techniques in one form or another. This guide will probably not cover every possible aspect of chronolocation, but I tried to make it as complete as possible. The tips and techniques range from going through source code or extracting metadata, to investigating sceneries depicted in a photo to determine a possible date or time.
Everything described in this guide contains common sense, basic physics and other verifiable techniques, but they must be used correctly before they can be admitted as evidence. It is also important to note that when using specific techniques for legal cases, it is advised to have them verified independently before admitting them to a court of law. Furthermore, I intend to make this a living document that will receive a new revision over time when there is enough new information to add. It would be nice if the community of OSINT, GEOINT and other INT's reach out if they feel there are any areas of expertise that should be included.
The word ‘chronolocation' comes from the Greek word 'chronos' (time) and the Latin word ‘locus' or the verb 'locare' for locate. In general, it describes the act of determining the moment something happened. It isn't a well-known word, but it seems it has been used for years already to describe the action of finding a date or time frame. Here is an abstract of ‘Gender and Song in Early Modern England' from 2014 using the same term when it talks about finding the time frame of a scene in the 1992 film ‘Orlando'.
The earliest mention of the word itself I could find takes us back to 1983, to the article 'Australian Sea Levels in the Last 15,000 Years' by David Hopley of the Department of Geography of the James Cook University of North Queensland. So, the word has been in use for quite some time already and due to the upcoming 'citizen journalism' the term is slowly gaining more popularity.
To make things a little complicated, the term is used in fiction novels as a term for 'time travelling'. But I won't be touching that subject in this guide, since that is in no way my area of expertise.
Geolocation and chronolocation have similarities when it comes to the investigative part of it, as mentioned earlier. Both require certain steps that need to be followed, or at least considered, and, as with any type of investigation, the credibility of the source is important. Since I was unable to find a good workflow for either, I propose the following for chronolocation, which of course can be adopted for geolocation with some adjustments:
Since the verification of findings in any kind of investigation is the most important, it is listed multiple times throughout this workflow.
In this article, several techniques will be discussed that can be used to determine dates or times. Starting with metadata in digital media, and ending with calculating shadows. Where possible, Quiztime quizzes are used as examples. This Twitter account is a great way to practice your verification skills, and in the past multiple quizzes needed chronolocation techniques to solve a question.
When media is acquired in a digital form, and a date or time needs to be determined, there are multiple ways of doing so, depending on the file type and the source it came from. First and foremost, it is important to check whether there is extra information inside the original obtained file, the so-called metadata. Within digital media there is usually extra information, which can be acquired by investigators. As an example, we can use a tool that can read the Exif data of a digital photo.
Exif stands for 'Exchangeable image file format' and specifies the format of information inside digital images and audio. Some images have an abundance of information, but it is also possible that it is stripped of all the information due to being uploaded to a social media platform.
Retrieving timestamps directly from digital files is a good start, but since a few years a lot of social media platforms are stripping the uploaded media from the metadata. Besides that, it is also possible to strip this information manually prior to distribution. And since the metadata inside the Exif tags consists of mostly plaintext data that can be easily changed or erased with easy to use tools, it can be one of the less trusted ways of determining a date or time. There are exceptions, for instance when the file is acquired directly from a trusted source, like a forensic photographer, or a member of a news agency, but in general my personal advice would be to treat Exif data as corroborating information and verify any date and time that is mentioned in a file, by investigating its content.
Photos on sites like Flickr, that preserves the Exif information, might look handy since the people uploading it wouldn't have a reason to change the data. But there's another problem on such sites, since there are quite a lot of photos that have incorrect timestamps for the location they show. One of the most common reasons is that people on holidays don't always adjust their camera settings to reflect the local time zone. So be prepared to verify all Exif data within photos from social media sites like Flickr if they need to be used for chronolocation.
To prevent such information ending up in your evidence, here's a tip by Christiaan Triebert: Try and contact the source, and verify the clock settings of the device that was used to capture the image or footage. Make a photo of the camera with a clock next to it that shows the current, local, time. This way you have the possibility to adjust timestamps if needed.
Besides Flickr and 500px that preserve full Exif information, there are some social media platforms that retain other valuable pieces of information, like the time of uploading. Even though the exact moment of uploading might not seem useful straight away, it can at least give some insight into the latest possible creation date of digital media. There have been instances where people made claims about a certain event, where the footage shown was uploaded months or years earlier, thereby refuting the story.
Finding metadata in websites or digital media is a subject that is very important for chronolocation, it’s too wide for the scope of this article. Therefore, I've created a separate guide on this that explains the basics. It shows the usage of simple tools, and how to retrieve information on some popular websites and social media.
Click here to go to the chapter 'Metadata in Digital Media'
When you have an image or video the chances are that these come from an online source. If so, it always pays off to investigate the metadata that comes with it. If that doesn't contain information that is useful, the next step is to dive into the minute details of the scene to look for clues that can indicate a specific date, time or time frame. Before going into that, let's first have a look at something else, the initial research question.
Within chronolocation there are several 'moments' that might be determined, depending on the need of that research question. Finding an exact time is not always possible, and sometimes not even needed. So it's important to determine whether finding the exact date is the goal. Answering that question can save a lot of time.
There are times that the research question is along the lines of: "Is the situation depicted possible, at the moment it was claimed?". Or maybe the situation calls for debunking a specific claim, where an 'earliest moment in time' is key. In such cases all one needs to do is to determine the earliest possible moment in time for the media that is being researched, because it's not always needed to determine the exact creation date of the media, since verification can be done by determining one parameter.
When looking for indications of the earliest possible moment one can look at objects or circumstances that were not present or have changed before the specific date itself. Examples are manufacturing dates of cars, or licence plates that are issued in chronological order. Another example can be the presence of a public transport vehicle that, that matches a specific time or day mentioned in that particular case. Other things to look for are the specific seasons, the local weather or construction work that was done in the area.
Just as it is possible to have the earliest possible moment, there is also the latest moment that an event has occurred, or the media was created. The research question or purpose is slightly different, but the approach is the same. For this you need to look at things that have changed after the moment in time that is claimed. For instance one can look for new objects after the time of the event, like new road signs or construction work that was finished.
Besides new objects, one can also look for things that have been removed after the claimed moment. This can be anything from mowed lawns to a building that was demolished. Anything that can bring down this date can be used to find the latest moment where the situation that is researched could have happened.
When the research question demands that a possible time frame must be established, one can combine the earliest and latest possible moments in time. This can also be used as the basis when trying to determine an exact date and time, since by first limiting the amount of possible dates, it will help to focus on the small details and eventually find the exact day.
This is not always an easy task but by going over small details in a photo or video, it's sometimes possible to find enough little clues to narrow down the possible time frame that a specific scene could exist. An example of narrowing down such dates can be read in this write-up of the Quiztime challenge of February 28, 2018.
When the exact location is known or determined, it's sometimes possible to calculate a more specific moment in time by using the angle and direction of the sun, if any shadows are visible. We'll have a more in-depth look at these techniques in chapter 6. Be aware though that there are a few important things to consider when using this technique:
The main thing is the exact location on earth. Due to the fact that the angle of the sun near the equator is completely different compared to a location that is further towards the north or south, it can be harder to determine a correct time.
Since the earth doesn't move nicely and calm in a circle around the sun, but has an oval shaped path, and even 'wobbles' while it rotates along its own axis, the exact location is important. Around the equator the sun sits high in the sky, moving faster in a horizontal way, but when moving further north or south, the sun is in a more shallow angle towards the horizon, appearing to move more slowly throughout the day. And the movement of the sun isn't only different throughout the day, but also during longer periods. Since locations further away from the equator have a more shallow angle throughout the year, and due to movement of the earth, it can result in less difference in angles at any given time.
To illustrate these points, here are two locations, where two moments in time are shown where the direction of the sun is nearly identical:
Location: Helsinki, Finland
Location: Hurghada, Egypt
In Helsinki it's possible to have the same time and azimuth, or 'direction of the sun', on two dates that are months apart. While these parameters change rapidly in Egypt when you jump even one or two weeks back or forth.
When the research question demands a specific date, it's best to start with a rough time frame and narrow that down with more information. For instance, one can use satellite imagery to look for large objects, like buildings, that have changed or demolished over the years. To narrow down the time frame even more, go over other sources that have information on the area. This can be news media, or even social media, as long as it has information with a date that makes it possible to look for differences. With this newly found information, the time frame can be narrowed down.
When the time frame has been narrowed down to less than about a year, it might be possible to determine the exact moment of time. For that, one has to look at the position of the sun, by going over shadows if they are visible. Overcast skies can make this step difficult or even impossible, since light scatters in different directions. And when shadows aren't clear enough to use, look for a general direction where the light comes from to determine the possible direction where the sun is sitting. This might give enough information to narrow down the possible time, but for that a possible date has to be determined first. To sum it up, the steps we need to take are:
If only the location is known, and there are no indications to narrow down the year itself, it might be possible to find a possible date and time without the actual year. Since the earth rotates around the sun in a very predictable pattern every year, it is sometimes possible to use tools to find the possible date, if the angle and direction of the sun can be measured precisely. How that works, will be explained in chapter 6.
When you are new to chronolocation, the best way to start, besides having a correct and trusted EXIF data of a photo, is to simply look at a scene. Go over it, try to describe the objects that are visible and find indications of a certain moment in time that these objects should have existed. Use the same techniques as you use for geolocation, and perform a 'gap analysis' to structure the information and research questions. You might end up with a period as large as a decade, or as small as a year. But depending on what you are investigating, it could even be a specific day of the week or a specific local time.
Sadly enough it isn't always possible to zoom in on a specific time or day, but there are also times that there is a lot to work with. I admit that I am sometimes blinded by lots of details in such a way that I miss some obvious clues. But going over all the information that is visible in a photo or video, as well as zooming in on those details, is extremely important. It's possible that while revisiting certain details after some time, one is able to pivot on other information that was gathered. Here are some examples of easy to spot things that can help you in the first steps:
To illustrate some techniques described above, I'll look at one of my all-time favourite challenges from Quiztime. Philipp Dudek asked two questions in this challenge: Where was the photo taken and what date? The location was reasonably easy to find for most people, it was the Danish embassy in Riga, Latvia. Knowing the location, we can have a first look at the photo to try and find clues that can be used for chronolocation. Give it a try before scrolling below the photo, to see whether you can already find some clues yourself.
As explained earlier, the first step in such a task is to narrow down the time frame. Since the photo was clearly taken in the digital era of photography, and the question was published early 2018, we have a period spanning well over a decade. And the most obvious indicators to narrow down the earliest possible moment, as discussed in chapter 4, are the earliest production dates of cars. To find the latest possible time, some time was spent to find out when security cameras were placed on the building across the street. The third indicator was a change in parking restrictions at a later date, due to the fact that the sign itself wasn't visible on the photo. By using these three pieces of information, it was possible to bring back the time frame down to about 3,5 years. After that, it was time to look at the season, pruning of a specific tree and by calculating the angle of the shadow, all of which will be explained in later chapters. If you want to read the full write-up of this geolocation and chronolocation challenge, you can do so here.
Large changes within the scenery might be spotted with something as simple as Google Earth Pro. There is also a web version, but I would recommend using the application for speed, multiple extra options and the ease of which one can save, import or export locations in the form of KML files.
One thing that can be of help when trying to determine a possible time frame, are events or festivities shown on posters, placards or such. These are usually placed several weeks before a big event, and even though they could still be around several months after the event, they can provide some indication of the earliest possible moment in time. When going over photos or videos that are taken in a city or even indoors, make sure to check things like:
Such posters and placards can also help with geolocation, since some countries have a very specific way of writing down dates. There are ISO standards when it comes to date notation, but there are some countries that have their own official standards. For instance, there are several countries, like Germany, Switzerland, Armenia and Romania, that write the dates using periods in between the numbers. These dates are always in the form of
dd.mm.yyyy, with or without the leading zeroes for the days and months. So one can be fairly confident that the days are mentioned first when there are dots used in a written date.
Plants and trees can give a very good indication of the season during the time a photo or video was created. If there are plants or trees visible that seem to be flowering, you could try and determine what plant it might be and when they are supposed to bear flowers or blossom. I do have to send out a small caution and remind you that certain crops or plants can flower in different months, depending on the location.
To give an example, it is common to see big fields of yellow rapeseed in the northern part of Europe and even in China from around April to June. But in Canada, where most of the yellow fields are Canola, a very similar scene will show up in June or July. And if we're talking about Australia, don't be surprised to learn this season falls in the months of August till October. To make it slightly more complicated, there are summer and winter versions of rapeseed, but usually the winter type has a higher yield, so it is more common to see them in the seasons I mentioned.
An example that was handed to me by MCantow, is the chestnut. In Northern Europe we can see the chestnuts hanging from the trees from around October until early winter, but there is more to that tree during the rest of the year. Besides having the seeds at the end of the year, it grows flowers in late spring or early summer, as can be seen in the photo above, and during the fall the leaves turn a lovely shade of red-brown.
In the following example, MCantow points out a European horse chestnut and a common lilac, that could be used to pinpoint the season.
Since the common lilac flowers in April and May in Europe, this narrows it down to two months. If the tree in this image is indeed the European horse chestnut, it would flower around the month of May. Since the distinct white flowers aren't visible in the image, this could mean that the episode may have been shot in the month of April, when the lilac would be bearing its flowers.
MCantow was also the person who spotted something very useful in the previously mentioned example of the Riga embassy quiz. In the photo a lime tree visible in the garden of the embassy, that was trimmed or pruned once every so often. After doing some research on this, we found out it is indeed common to prune a lime tree every two years, because this is the best way to keep it in a healthy shape. By comparing images from this particular tree over longer periods of time on Flickr, we were actually able to estimate in which specific months over the years that tree was pruned, and therefore helping us in finding the actual date.
But there are enough plants and trees that might be of help to determine a season, or even a possible month. Here are a few examples that I wanted to share since they blossom or flower in specific areas at very specific times. Do be careful and use this only as a rough guide, and always make sure to check local flora to make sure that you have the correct species when looking at specific plants or trees.
|Lavender||June||Cape Verde and the Canary Islands, and from Europe across to northern and eastern Africa, the Mediterranean, southwest Asia to southeast India|
|Cherry Blossom||March to April||Mostly Asia, but there are a few locations in Europe and North America where cherry blossoms can be found in parks|
|Poppies||April to June||April to May in Southern Europe, May to June for more northern countries|
|Witch-Hazel||September to March||USDA zones 3 to 8 (North America), it's special since this tree actually flowers during the winter months|
More information about the 'USDA zones', or hardiness zones, can be found at the Wikipedia page. This can be used as a reference, or to verify specific plants or trees within a geographic area.
There are many more factors you can use to bring down the date or time when it comes to chronolocation. If you are observant enough, and use every bit of information that is available, it'll open up a world of possibilities. In the next example people found out the time the photo was taken, by paying attention to the helicopter that was mentioned. After geolocating the photo, they looked at the flight data that was available of that area, and came up with the exact time.
To track air traffic, a website like Flightradar24 can be very useful. There are other websites that offer the same functionality, and with paid accounts it's possible to get more historical information on air traffic.
The free tool Google Earth Pro can be extremely helpful since it has historical imagery from nearly every location on the planet. This dataset can be found in the menu bar, by clicking on the small clock icon.
After clicking on the menu button, a small slider appears showing the date of the imagery that is currently showing. The slider shows light blue marks on dates where it features a dataset. Sliding throughout the dates will reveal these images on the screen. Going over the historical imagery can be useful to find changes in the landscape, as discussed in paragraph 5.1, but can also be useful to see what shadows look like in a specific location.
If there is no clock visible in a photo or video, another way to determine a date or time is to use shadows. For multiple investigations I had to use this to try and determine a solid time frame, even though it can be a very challenging task at times. Some media are just downright poor in quality, or shadows are in very unfortunate angles to make it more difficult to work with it. But first let me explain something about the process involved.
First, the earth revolves around the sun, what we call the earth’s revolution and the trajectory that the earth makes is shaped like an ellipse. While we spin around the sun once a year, the earth also rotates around a vertical axle that is slightly off centre. The tilted axis, together with the rotation around the sun gives the earth it’s four seasons.
Because the rotation of the earth and the trajectory around the sun is extremely predictable, we know that at any given day and time the sun is in a specific position. During a summer in the Northern Hemisphere the sun is high up in the sky, while the winters have the sun much lower towards the horizon. On the internet there are several tools available that can calculate the exact position of the sun at any given day or time. To use this for a calculation, the only thing needed are the angle in comparison to the horizon (the zenith or altitude) and direction of the sun (the azimuth). With these two pieces of information, anyone can calculate the possible date and time of any given shadow.
Due to the trajectory of the earth and its rotation, there are two dates a year when the sun is in the same position, called the equinox. These dates are around March 20 and September 22. Looking at the moment of the equinoxes, we see the following pattern emerge:
|Latitude||March equinox||September equinox|
|90 N||0 degrees||0 degrees|
|60 N||30 degrees||30 degrees|
|50 N||40 degrees||40 degrees|
|25 N||65 degrees||65 degrees|
|0 N||90 degrees||90 degrees|
|25 S||65 degrees||65 degrees|
|50 S||40 degrees||40 degrees|
|60 S||30 degrees||30 degrees|
|90 S||0 degrees||0 degrees|
Before we can start calculating a time or a date, a few things are important to know, namely:
If all these conditions are met, then it is not only possible, but even fairly easy to determine the date and time when that photo or video was taken.
As a first example, we'll go over an old Quiztime question, with a photo that was taken on Thursday, June 7, 2018. The date was given, and the time had to be determined.
For this, we first need to find the exact location of this image. This isn't so difficult, and after some reverse image searching, it gives us the answer: It's a large artwork at the foot of the Atomium in Brussels. We only need to establish where it is located exactly, and from which angle the photo was taken.
Measuring the angle of the artwork, gives us a deviation of 5 degrees, in comparison to true north. We can measure this fairly easily by using the ruler in Google Earth Pro.
Looking at the image itself, we can see a shadow that was cast by the woman standing in front of it. This gives us the indication that the sun was standing south, with an azimuth of 185 degrees. When we line up the base of the artwork (green) with the direction of the shadow (red), we see that they run nearly parallel.
If we want to be even more precise, we can zoom in on the image itself to check whether the shadow is indeed in line with the artwork itself, or slightly off. When we look at the shadows, it seems that there is a slight difference, but the difference is so small, that this would be maybe half a degree deviation.
To find out what time this was possible, we open the website SunCalc. We first need to find the exact location, and for that we can simply search for 'Atomium' (A), and it'll give us a list of possible locations. Selecting the location in Brussels, we then set the date to June 7, 2018 (B) by clicking on the date field. We can then move the slider on the top bar (C) until we get close to the desired azimuth. To get as close as possible, we can adjust the minutes manually, by clicking on the time field, and adjusting it accordingly. The time given on the website is in local time, and is adjusted for daylight saving time automatically.
After matching the altitude and azimuth of the sun, we find that the time that this photo was taken was around 13.53 local time. The actual time was around 14:00, which is only a few minutes off, which is a good result.
A more difficult task is to try and find a time and date. For this, we also need to look at the altitude of the sun, besides the azimuth. Since the height of the sun is changing throughout the seasons (remember the 'low sun' during winters in the Northern Hemisphere), we need to take that into consideration.
To calculate a possible date and time, in general the following steps are necessary:
After that, there should only be one specific moment in time left. If this moment is very close to a solstice, it is possible that two moments in time match. This will need further elimination, if at all possible. To see how this process works, I'll use the following Quiztime challenge by Julia Bayer:
The first step is to find the location. This turns out to be the Haus der Kulturen der Welt, on the river Spree in Berlin. We'll need coordinates of the possible location in a bit, so we write them down: 52.5195441,13.3649990. The second step is to determine the height of the object and the shadow length, so we can determine the angle of the sun. Do make sure you select the correct point when visualizing the path of the sun rays. Imagine how the rays hit a specific part of the glass, and where on the surface they cast a shadow.
One option to calculate the altitude of the sun is by measuring the amount of pixels, both for the object height and the shadow length. For this you can use Photoshop, The Gimp, or any other program that enables you to load an image, and to draw a line to measure the amount of pixels. Because it's irrelevant what units of measurement we use, we don't need to use millimetres or metres. What we are interested in, is the angle between the vertical and horizontal plane of the right-angled triangle we created. By entering the height as the amount of pixels of the object in Suncalc, we can then slide the sun left and right until we have the desired length. Another option is to calculate the angle manually with the following formula:
α = arctan(height / shadow length)
If it's been too long ago that you've used a calculator, or rather like to use online tools, then there are multiple websites that can help you. One of them is the website calculator.net, that have a module for right triangles. Fill in the height of your object under a, and the length of the shadow under b. After pressing the button, the altitude of the sun will be calculated and shown as α.
Whichever method is used, this will give us a value of about 25,6 to 25,7 degrees altitude. If we want to find out at what moments in time this altitude and azimuth occurred, we'll be using the website SunEarthTools.com. On the website, we pick the menu option 'Sun Position'. This page has several tools that revolve around the location of the sun. The option that is most interesting is the 'Annual sun path' section. You can scroll down, or jump to it straight away by clicking the option directly under the map section.
I've noticed that the adjustments for daylight saving time isn't working as it should. I've turned that option off, and calculate everything in time zone GMT+0. I adjust the times later on.
This option will generate an Excel sheet with altitudes and azimuth of the sun throughout a whole year, based on a given location. For this we fill in the details, like the location and the year, and then choose and the steps, or increments. The sheet can be generated in increments of 5, 10, 15, 20, 30 or 60 minutes. In general, I would say: The closer to the equator, the smaller the increment. For this an increment of 15 minutes is enough, and will generate a sheet of about 1MB in size. In this case, I chose the previously mentioned coordinates: 52.5195441,13.3649990.
It technically isn't really an Excel sheet, but an HTML table. Excel will give a warning when opening it, and will convert it accordingly if you continue.
After opening the sheet it'll show all the dates of the year in the first row, and in the columns it'll have the different times in 15 minute increments. Per timestamp, it has one column starting with E for elevation, and one starting with A for azimuth. To visualize what I'm looking for, I personally like to highlight cells that fall in between certain ranges by using the 'Conditional formatting' option. This option is also available in the open source app Calc in LibreOffice.
In this case, the altitudes and azimuths are far apart, so it's enough to create two rules for the whole sheet, where cells will be highlighted in different colours when they fall in between different values. If the azimuth and altitude are very close together, consider using the same colour for highlighting, or create a rule for the different columns. To do this, pick the menu item 'Conditional Formatting' and use the option:
Highlight Cells Rules - Between.
This option gives us the ability to highlight cells that have a value within a specific range. To find the possible values for that range, play a bit with SunCalc and move the sun back and forth, to get a rough idea what the direction of the sun could be. Find the minimum and maximum values for the azimuth, by comparing the direction of the shadow to the image or video you're investigating.
After determining these values, the altitude was determined to be between 26 and 27 degrees, since that is the angle of the shadow. The azimuth has to be somewhere in between 262 and 264 degrees. After assigning different colours to these values, a pattern will emerge within the sheet, as can be seen below.
Depending on the language settings on your system and in Excel, it's possible that the numbers will be seen as text and the cells won't be highlighted. To correct that, select all the cells by clicking in the left top corner, or pressing Ctrl-A or Cmd-A, and replace all periods with a comma.
After that, it'll be easy to find the possible times by looking at the moments where both the altitude and azimuth fall between the ranges we provided. The only period where this is possible is between August 3 and August 7, 2021 around 16:45 in the afternoon. Given the fact that Julia mentioned the photo was taken on a Thursday, there's only one option left.
If you're not using Excel, or any open source options like LibreOffice, another option is to go over SunCalc.org manually and pick two or three dates per month, until the altitude and azimuth gets closer to your desired values. After a rough period has been established, it's possible to move towards the desired dates. But by using the export provided by SunEarthTools, it's possible to determine a possible time frame easily, quickly, and accurately.
Accurate chronolocation is only possible if there's enough information to go on. But there are times when the media being investigated is hard to interpret. Shadows might be coming from different directions, or hard to make out. Or the photo doesn't lend itself for accurate measuring of the shadows. But usually there are always some things that can be tried, to enhance a photo, or work with the information that is visible.
There are moments when a shadow isn't very visible, but there are ways to enhance the image to make measuring more easy. There are different options you can use, to make the shadow more visible. Within Photoshop for instance, tools that could help are:
An example of an old Quiztime quiz, where such adjustments have been made can be seen here:
Using that same photo of the fire department pickup, there's another thing that's just about visible. When zooming in on the windows, the brightest part of the sky is on the right side of the visible windows. Since the shadows seem to indicate that the sun is nearly in a direct line of our viewing direction, it makes sense that there is a possibility that the sun is visible in the reflection, here marked in yellow.
If the shadows on the photo of video are not aligned horizontally, it will make measuring the exact angle more difficult. Since we live in a three-dimensional world, the length of a shadow is sometimes difficult to measure when it's falling towards you. Here are two examples, both taken in the same area.
Luckily there are possibilities to measure the distance of a shadow fairly accurate, by using elements of the environment as guidance. Try and find items of which the exact size can be determined, of find something that can be used to measure the shadow as accurate as possible. Street tiles can be extremely helpful, by using them as a grid, for instance.
Let's have a look at an example, again at the Louvre, where the shadow is not plotted horizontally on the image. It is still possible to use the tiles as a grid, and calculate where the shadow would be when positioned horizontally in the photo, therefore making a calculation possible. First we need to establish where we would like to have our shadow in the image, and draw a horizontal line that we'll use for guidance later on, so we can determine were the shadow would fall if it would be rotated anticlockwise.
Next we recreate the grid with the correct proportions, and we will recreate the position and length of the shadow. This can be a simple line, from the object, or in this case a person, to the furthest point of the shadow.
Then we draw a circle in our grid, where the centre of the subject itself is also the centre of the circle itself. To find the centre, visualize how the highest point that is able to create that shadow, extends directly downwards to the ground. This will be the centre that we need to use to draw a circle. The radius of this circle extends towards the end of the original shadow, show here in yellow.
After lining up the horizontal line in the photo, and the radius of the circle, we find a new point where the shadow would fall, if it would be rotated anticlockwise. When measuring the original image in Photoshop, I found a length of 830 pixels. When comparing this to the length of the original shadow in the image, we find that it's only 625 pixels long, and therefore roughly 30% too short to be used for an accurate calculation.
If it's unclear what a shadow, for instance cast by a building, could look like in a specific area, then it's possible to recreate it using freely available tools. One of the simplest ones I've found so far, is ShadowCalculator. It has the option to create a virtual building on top of Google Maps, placing points on the map to create a shape.
Every point in the shape can have its height adjusted, making somewhat more complex shapes possible. By adjusting the date and the time on the right side of the screen, the shadow and its shape will be adjusted on the map.
When going over images and videos, looking for shadows, there are a few things to be careful about. If you're new to the game, there are some situations that could lead you to different dates or times. One thing to be careful about, are clouds in the sky. Sunlight that travels through a cloud can scatter the sunlight, whereby the clouds are acting as a diffuser. This will make the edges of the shadow harder to distinguish, information we actually need to determine a correct altitude. Besides that, it can also make it very hard to distinguish the shadow from darker surfaces like asphalt.
Another thing to be wary about are reflective surfaces. Especially in modern cities, with large glass facades, with reflective windows. Looking at the example, we can clearly see the sun being reflected in the large building, thus sitting in a location somewhere left of the photographer. But due to the reflective surface of the building, all the shadows fall towards us.
To determine the exact direction of the sun, one would have to zoom in onto the right bottom of the photo. The woman walking there is not lighted by the reflection of the sun. By using this bit of information, it's possible to determine the correct location of the sun after all.
This concludes this comprehensive guide on chronolocation, and I hope it gives some tips, tools and hints for people that are just starting out with this. The most important thing in chronolocation is always: Pay attention to details, verify what you're seeing, and use knowledge or information about a specific area to get a better understanding of the situation. Whether it's asking an expert to determine whether crops are harvested already, searching the internet for information on dry and wet seasons, what plants are flowering at any given time and so on.
By combining all that information, and looking at multiple sources to narrow a time window down to a year or a few months, it's time to dive into the details. Hopefully you have shadows that can guide you, or maybe there's a sale at a shop that is visible in an image you're working on. It doesn't matter how small the clue, sometimes a simple no-parking sign can break a case open and enable you to determine the exact date within reach. So go out, take some photos in different situations, or go over your old archives, and practice. Make sure your EXIF information is correct, and see whether you're able to find out when you took a specific photo.
I'm closing off by saying that this guide is not finished yet, and will probably receive some updates in the upcoming months or so. There are also some topics I want to include over time, expand on certain paragraphs, or write down some tips even more clearly. But due to time constraints (I know! It only took me over 3 years), I had to finish this guide to be released early November 2021.
The term altitude is used to describe the angle in degrees of the sun in relation to the earth's surface. An altitude of 0° means at ground level, and 90° means directly overhead.
The arctan is the inverse trigonometric function of the tangent function, which is the ratio of the side opposite an angle divided by the side adjacent to the angle. It is used in the following formula, that calculates the angle, or altitude, of the sun:
α = arctan(height / shadow length)
This term is used to describe the direction where the sun is standing, in relation to true North. This means that at an azimuth of 180°, the sun will be in the south.
Diffused or soft light is the situation where the sunlight is scattered. This can be due to clouds, or because the sun is set very low, and bounces off the atmosphere.
An equinox is the moment the plane of Earth's equator is at a 90-degree angle with the sun, so the centre of the visible Sun is directly above the equator. This occurs twice each year, around March 21 and September 23.
The solstice is the moment where the sun is the furthest away from the equator, and happens around June 20 or 21, and December 20 or 21. They are called respectively the Summer Solstice, and Winter Solstice. In June this results in the longest day of the year, and the shortest day in December, when you're in the Northern Hemisphere, and vice versa in the Southern Hemisphere.
SunCalc is a tool that enables you to recreate the location of the sun during any moment in time, at any location on earth. The link to the website is: https://www.suncalc.org/
The website SunEarthtools provides multiple tools that can be used to create an overview of sunrise and sunsets, or export Excel sheets with altitude and azimuth information. The link to the website is: https://www.sunearthtools.com/
First, I want to thank everybody of the Quiztime crew for sending out daily verification quizzes. I've learned a lot from these, and have been able to broaden my knowledge over the last few years. I also want to thank Christiaan Triebert and Aliaume Leroy for taking the time to review the information and giving tips. And most of all I need to thank someone very special to me, who had to miss me for hours on end, while I was writing paragraph after paragraph, and doing research during holidays.