As described in my last post, I was inspired by an APOD entry last December featuring a solar analemma captured by a security camera on someone's driveway to create my own timelapse video tracing the path of the Sun over a year, capturing the distinctive figure eight shape of the analemma as the shadow moves day by day. This project recreates a technique used for timekeeping, calendar making, and as the basis for religious and cultural rituals going back thousands of years. But as with the APOD that inspired it, I'm putting a modern spin on this ancient concept by leveraging programming, computers, digital cameras, photo and video editing software, design software, and 3D printing. In this post, I'll provide an overview of my setup, including how I planned out the project, created a custom gnomon (the part of a solar timepiece that casts the shadow), set up the camera and automation system, and the initial image processing and results.
Decision #1: What to Shoot With
Blink camera
First off, I had to pick a camera to capture each image with. As the subject is outdoors - and the project lasts for a year - using a DSLR like my Nikon D750 wouldn't be feasible. I could easily dedicate one of the IP cameras I have for a year but they aren't weather-proof and they have to be plugged in. Luckily, we have a set of Blink outdoor cameras around the house. They are weather-proof, battery-powered and can be accessed over a network connection. The only concern I had with them is the mount is easy to move which could interfere with having the same point of view for every image over the course of the year. I solved that by 3D printing a new mount that I could lock in place with a set screw.
Decision #2: Where to Shoot
My first thought was to do something like in the referenced APOD... shoot to the north with the shadow to track being cast in front of the camera with the Sun shining from behind. I even considered mounting the camera so that its own shadow would be what traces out the analemma. However, while our house faces north-northeast, we have 6 huge cedar elm trees out front; during the summer any shadow cast from the edge of the house would be lost in the shade of the trees. Given that, I settled on shooting in the back yard.
Decision #3: When to Shoot
View to be captured
The decision of when to shoot and where to shoot go hand-in-hand. Deciding to shoot in the back yard was fine but incomplete till I figured out what time of day to shoot. Long story short, as we already have a Blink camera on our side fence, I figured out that as that fence runs on a line that's about 153 degrees (approximately south-southeast), I could shoot at just after noon each day and the shadow would trace out the figure eight of an analemma on the ground just on our side of the fence and in the field of view of that camera.
Decision #4: What to Shoot
Gnomon on fence
Although I could have mounted just anything on top of the fence to cast a shadow, I took advantage to having access to a 3D printer and designed and printed my own gnomon in the form of a stylized Sun mounted on a post. It was printed in black but I took yellow Plasti-Dip both for a "sunny" look and also to give it a bit of additional protection against the elements.
Decision #5: How to Shoot
Early photographic attempts to capture a solar analemma in the sky with a film camera required incredible dedication, shooting at the exact same time of day, one day a week or every few weeks for an entire year. Because I am creating a timelapse video rather than a composite photo, I need to capture an image more frequently (every day) so I decided to automate the process. I have a home automation solution called Home Assistant. With it, I was able to write a script that takes a photo with the Blink camera in the back yard at 12:30pm (1:30pm during Daylight Saving Time) every day. The system also records metadata about weather conditions (overcast, sunny, etc.) in a text file, storing both the images and data on a home computer for later use in assembling the video.
Progress To-date
Although I only recently began posting about this project, I started planning it in December and started shooting the day after the winter solstice which fell on December 21st. Things are going well but there have been a few bumps in the road:
It turned out that the shadow cast by the first gnomon I created was a little too small so I redesigned a larger version and replaced the first one with it at the end of December.
Although the camera mount is locked in place, it appears that the image framing shifts a very small amount over the course of several days. My guess is that the weather going from sub-freezing to springtime temperatures, the plastic mount is expanding and contracting, affecting the alignment of the camera. Thankfully, the difference from image to image is small enough that I can align all the images using Photoshop so that they don't shift from day to day.
Early on, rain left water drops on the camera lens that affected the images but we've had quite a bit of rain since then and it hasn't happened again. If it does, I may need to add a hood to the camera mount.
In spite of these issues, my first pass at assembling the images into timelapse format looks promising. This version has two sections. In the first, watch for the yellow dot on the ground... it overlays the gnomon's shadow. In the second section, watch that same area of the ground and you'll see the shadow of the gnomon trace out the beginning of an analemma.
Timelapse showing 6 weeks of daily shadow captures (with gnomon shadow highlighted and with raw video)
As you can see, at just 6 weeks, there is not enough of the analemma yet to make out its distinctive figure eight shape but a pattern is beginning to take form. And there are some oddities in the video - gaps from overcast days (and some rain) and other things moving besides the shadow cast by the fence and gnomon (leaves, chairs, our dog, etc.) - all things I expected given my past experience creating timelapse videos.
But how exactly did I create the gnomon? What tools did I use to automate the daily image capture? And what techniques am I using to process and align the images? To create the video? In my next post, I'll dive into these technical details and more, sharing the nuts and bolts of my analemma timelapse setup for those who want to explore further.
If you follow the Astronomy Picture of the Day (APOD) like I do, you may have seen the December 2024 entry showcasing a photographer in Colorado who used a security camera to track a shadow on their driveway at the same time each day for nearly a year. As the seasons changed, this shadow traced out a distinctive figure-eight pattern known as an analemma. I found the simplicity and ingenuity of using readily available technology to capture such a complex phenomenon fascinating.
What caught my attention wasn't just the clever use of a security camera to track the sun's movement, but how it connected ancient and modern ways of marking time. Most of us have seen sundials in gardens or parks, where shadows mark the time of day. Fewer people are aware of solar calendars, like the Noon Mark on the south face of the Royal Observatory in Greenwich, which uses carefully placed markers to track a shadow's position at noon throughout the year, forming the same figure-eight analemma shape. In the video above, here was someone using modern technology to capture the same astronomical pattern that astronomers and timekeepers have been tracking for centuries.
Inspired by this APOD, I decided to capture a shadow analemma using technology myself. I'll dive into the details of that in my next post, but first, I’d like to share a bit of historical and scientific context.
The word analemma comes from ancient Greece, where it originally referred not to the figure-eight pattern itself but to the mathematical techniques used for calculating the Sun’s position in the sky. It was derived from the Greek word analēmma, which referred to the support or pedestal of a sundial. In astronomical terms, however, analēmma described the methods used to account for the variations in the Sun's apparent motion throughout the year. This early use of the term was central to creating accurate solar calendars and tracking celestial events.
In modern usage, analemma now refers to the distinctive figure-eight pattern traced by the Sun's position in the sky when observed at the same time each day throughout the year. This pattern arises from two astronomical phenomena: the tilt of the Earth's axis and its elliptical orbit around the Sun.
The Earth's axial tilt of 23.5 degrees is the easy part of the pattern to understand. Because of this tilt, the Sun appears lower in the sky during winter and higher during summer in the Northern Hemisphere, with the opposite occurring in the Southern Hemisphere. If this were the only factor, the analemma would form a vertical line rather than a figure-eight, as the Sun's position in the sky would rise daily between the winter and summer solstices and descend daily between summer and winter.
However, because the Earth's orbit around the Sun is an ellipse, it is closer to the Sun around January and farther from the Sun around July. According to Kepler's Second Law, an orbiting body moves faster as it is getting closer to the body it orbits and slower as it is moving farther away. When the Earth is speeding up, the Sun appears a little ahead of its average position in the sky (i.e., where it would be if Earth's orbit were a perfect circle) and, as it is slowing down, it appears a little behind its average position. This, combined with the Sun's changing elevation through the seasons, creates the figure-eight pattern.
Long before cameras could record the Sun's position in the sky, ancient civilizations from Egypt to China used a down-to-earth approach to track time: observing shadows cast by the Sun—patterns that, over time, reflected the effects of the analemma. They built elaborate structures specifically designed to mark the passage of days and seasons by the position of shadows. These structures were not just timekeeping tools; they were woven into religious and cultural traditions, guiding agricultural cycles and celebrations.
In the modern era, photographers have found a new way to capture the Sun's path: sky analemmas. By mounting a camera in a fixed position and taking photographs of the Sun at precisely the same time each day throughout the year, they create composite images showing the Sun's position tracing a distinctive figure-eight pattern across the sky. These images have become iconic astronomical artworks, requiring dedication and precise timing to create. However, they offer a more abstract way to visualize the Sun's movement—one made possible by photographic technology.
Shadow analemmas are particularly intriguing because they translate this celestial pattern into something tangible. While sky analemmas show where the Sun is, shadow analemmas reveal the effect of the Sun's position on our immediate environment. By following the Sun's path through the shadows it casts on familiar surfaces, we can experience the same astronomical phenomena that guided ancient timekeeping. Shadow analemmas can bridge historical traditions and modern science.
In this project, I seek to unite ancient astronomical practices with modern technology by developing an automated system to capture a year-long shadow analemma. Throughout this series, I'll explore the technical details of my setup, the challenges I've encountered, and the insights I've gained. Join me on this journey to explore the intersection of astronomy, photography, and the rhythms of everyday life.
If you read my previous post on the RadioLab / IAU story of quasi-moon named Zoozve and the contest to name another quasi-moon, you may be happy to hear that the finalists have been selected and it is time to vote!
Although I thought my submission, Zephyrus, was a great name for a quasi-moon, unfortunately the panel reviewing the submissions didn't select it. But given they had over 2,700 entries to pick from, I guess my odds were pretty long anyway. 😲
Here are the names they selected as finalists:
Bakunawa - a mythical dragon from Philippine folklore
Cardea - the Roman goddess of doorways and transitions
Ehaema - the "Mother Twilight" from Estonian lore
Enkidu - the wild and noble companion from the ancient Sumerian Epic of Gilgamesh
Ótr - a shape-shifting dwarf from Norse mythology
Tarriaksuk - shadow beings of Inuit legend that mirror human forms yet dwell in another dimension
Tecciztecatl - an Aztec lunar god who once aspired to be the sun
Care to join me in voting for one of these 7 to be selected as the formal name of quasi-moon currently known as (164207) 2004 GU9? We have until January 1st, 2025. You can cast your vote here!
The journey continues beyond 2009... check it out!
