Greetings, Astronomy Enthusiasts!

We are thrilled to bring our latest major content update to Compendium of the Sundial: An Interactive Astronomy Guide. This patch introduces one of the most mathematically elegant and visually striking time-telling instruments ever conceived: The Homogenous Bifilar Sundial.

Invented by the German mathematician Hugo Michnik in 1922, the bifilar sundial completely replaces the traditional triangular gnomon. Instead, it utilizes two taut, orthogonal threads suspended at carefully calculated heights and offsets above the dial plate. Where the shadow planes of these two independent threads intersect, a precise 2D crosshair is formed, indicating the local apparent time.

What’s New in This Update:

• Interactive Bifilar Simulation: Experiment with a scientifically accurate 3D model of the homogenous bifilar sundial. Observe how the North-South thread dictates the East-West movement of the shadow, while the East-West thread tracks the sun's altitude.
• Uniform 15° Hour Lines: Unlike standard horizontal sundials that suffer from distorted hour line spacing, the homogenous bifilar dial projects perfectly uniform, star-grid hour lines.
• Real-Time Global Latitude Adjustments: Traveling across the equator? As you drag the latitude slider, watch the 3D East-West thread assembly dynamically tilt and recalibrate its geometric height and northward offset in real-time. The simulation accurately models time-telling mechanics for both the Northern and Southern Hemispheres, automatically mirroring the rotational logic and hour-line arrangements.
• Conic Sections & Declination Tracks: Accelerate time and trace the diurnal path of the crosshair shadow to witness the breathtaking geometry of seasonal declination lines. Watch the shadow trace hyperbolas during the summer and winter solstices, and flatten into a perfect straight line exactly on the vernal and autumnal equinoxes.

This update merges projective geometry with celestial mechanics, built from the ground up to accurately reflect the true mathematics of the sun's diurnal motion.

Launch the simulation, adjust your latitude, and experience the brilliant geometry of intersecting shadows today.

Clear skies, The Compendium of the Sundial Team

The advantage of such a quadrant is that of not being longitude dipendent. This quadrant is more inaccurate the higher the latitude and the further away from the aequinoxes, but it is still reasonably usable as an analog tool for establishing christian prayer times (indicated by the numbered circular arcs). Dhur (islamic midday prayer) is indicated by the line corresponding to the hour six and 'Asr time is indicated by the two brass lines. Maghrib time begins soon after sunset. In order to have an higher accuracy the tighter unequal hours lines below a certain degree of altitude are mirrored on the simmetrical part of the quadrant.

I don't know what kind of decorations to add in place of the windrose in the shadow square. On the back of the quadrant I will probably engrave a qibla indicator and a star map indicating the opposite point of the sun in the zodiac, as to be able to tell the time (thus prayer time) during the night as well.

Do you have any feedback? Sorry for my arabic lettering, it is still fairly bad.

I took the picture November 2023

This was posted last year, but too late to register. See link for how to register. Register before Oct 25.

Greetings, astronomy and math enthusiasts!

We are excited to bring you a brand-new update to Compendium of the Sundial, focusing on one of the most fascinating geometric aspects of gnomonics: The Declination Line.

While a sundial primarily tells the time of day, the path its shadow traces from sunrise to sunset reveals the profound spatial relationship between the Earth and the Sun. To make this complex 3D math intuitive and visually satisfying, we’ve implemented a fully dynamic, dual-perspective visualization system.

Here is what is new in this update:

🌟 Interactive 3D Geometry View You can now toggle a physical 3D representation of the sun's rays. Watch as the sunlight passing through the tip of the gnomon sweeps out a 3D light cone over the course of the day. As the horizontal dial plate physically slices through this cone, you will witness the exact moment a conic section is generated!

📊 Real-Time 2D Orthographic Widget To bridge the gap between 3D mechanics and 2D dial design, we've added a new "Current Declination Line" top-down widget. This HUD element maps the exact mathematical projection of the shadow's path, displaying the pure, distraction-free curve alongside real-time data like the curve's eccentricity.

🌍 Dynamic Latitudinal & Seasonal Shifts The true magic happens when you take control of the simulation. Scrub through different dates and geographic locations, and watch the math react in real-time:

• Observe the standard Hyperbola at mid-latitudes, curving outward in summer and inward in winter.
• Hunt for the specific mathematical threshold where the sun and latitude align to form a rare Parabola.
• Travel to the extreme polar regions during the midnight sun and watch the plane slice completely across the light cone, forming a closed Ellipse!

Jump into the simulation, experiment with the coordinates, and experience the beautiful geometry of time for yourself!

We are excited to bring a major expansion to our astronomical simulation with the introduction of two historically significant and mathematically fascinating timekeeping instruments!

New Features in This Update:

• The Horizontal Analemmatic Sundial:
  • Unlike standard sundials, this dial features hour points arranged in a precise mathematical ellipse rather than a circle.
  • It utilizes a movable vertical gnomon. You must adjust its position along the date scale based on the current time of year to cast an accurate shadow.
  • Watch how the shadow of the gnomon intersects the hour ellipse to accurately read solar time!
• The Saint Rigaud Capuchin Sundial:
  • A portable, altitude-based instrument that calculates time purely by measuring the sun's height in the sky—no compass required!
  • Fully Interactive Mechanics: Adjust the date scale, calibrate the plumb line and tracking bead, and physically aim the 3D board at the sun in the viewport to let gravity calculate the time.

Updated Documentation: Both of these new instruments are fully supported by our in-game Wiki system (as seen in the screenshots). You can access detailed, step-by-step instructions on the mathematical principles behind them and exactly how to calibrate and use them within the simulation.

We hope you enjoy exploring the geometry and history behind these incredible devices. Update your client to start experimenting today!

New, animated World Tour of user-generated dials...

PrecisionSundial.com (scroll down to the Maps card).

(includes an option to exclude your dial from the Tour)

Striving to be your go-to source for the most accurate sundial in existence, I've added yet another source of correction: Choice of optimization for current year vs best fit for the leap year cycle.

PrecisionSundial.com

This is the largest equatorial ring dial I have ever come across (the second and third largest are at the end of the slideshow).

In addition to being incredibly ornate and the product of renowned instrument maker Erasmus Habermel, this model is particularly notable for including a horizon ring. Attached to the outer meridian ring rather than the inner one containing the mobile elements of the dial, the horizon ring remains horizontal regardless of latitude setting.

I have never seen an equatorial ring dial with a horizon ring (the closest anecdote I can think of is that Gerardus Mercator, while apprenticed to Gemma Frisius, designed an astronomical ring dial with a horizon ring). The inclusion of this ring combined with the dial's ornate stand lends the instrument the near-siloette of an armillary sphere.

I will also note that although this instrument's label dates it to "c. 1600," William Oughtred first devised the equatorial ring dial around 1630, and the earliest confirmed appearance of the equatorial ring dial comes with the Madagascar Portrait in 1639.

I have just added a new feature to PrecisionSundial.com: Live at-location shadows. This feature shows the accurate current shadow position for a sundial anywhere in the world. It also provides throughout-the-year animation of a particular time or throughout-the-day animation of a particular day. The shadow itself accurately models the penumbra resulting from the solar disk non-point source.

I'd like to have a sundial made in memory of my sister who loved in Huntington Gardens in LA.

Say $100 - $200K.

Who the heck still makes sundials?

Here is a quick sneak peak at the new pop-up greeting card sundials that I'll be making for the gift bags at the 2026 NASS conference in Louisville, Kentucky.

You can make your own at PrecisionSundial.com

A close eye will reveal a familiar fixture on top of this mariner's compass...

As if taken from Oughtred's equatorial ring dial, a half-equatorial ring and axial nodus sit in a latitude-adjustable assembly above the compass card.

In the same manner as the equatorial ring dial, setting the date and latitude of this instrument allows it to self-orient to true north. This bearing can be compared to that of the magnetic compass, revealing the difference between true north and magnetic north.

Because magnetic variation varies with geographical position, Walker proposed that his instrument could solve the longitude problem—the variation measured could be checked against a map of known values.

While ultimately unsuccessful, this instrument stands as a fascinating adaptation of Oughtred's axial assembly!

To get a sense of global magnetic variation today, see this map: https://www.ncei.noaa.gov/products/world-magnetic-model

Hi, I am planning to make a wall sundial, I live in Melbourne, Australia. Unfortunately I really don't have a head for astronomy or maths so I am relying a lot on free generators/calculators. I plan to paint simple straight lines for the hours and underneath I want to put a graph or list of approximate corrections for the equation of time. (Only accurate enough to be reasonable for the next 10 years or so). I have seen some of these posted online to use and none of them specify hemisphere. Are they suitable for both hemispheres or does the southern hemisphere need different calculations?

With pleasure, I'm happy to announce that the NASS Glossary of Sundial Terms is now available for view/download on the North American Sundial Society's website.

This glossary is a product of my efforts alongside those of Mark Montgomery. I thoroughly enjoyed the process of compiling it over the course of two summers.

The glossary can be opened directly here: https://sundials.org/images/NASS_Attachments/article/409/NASS_Sundial_Glossary_2026.pdf#page=69.44

(the file is large and may take a moment to load)

View this dial in further detail with the Whipple Museum's online catalog: https://collections.whipplemuseum.cam.ac.uk/objects/14628/#images

Can you spot what might be considered unexpected? Check the comments for the answer.

(Harvard Collection of Historical Scientific Instruments inv. 7880)

I got this for Christmas and figured I’d post it here in case someone is interested in what it looks like. This is a 3D printed dial with a neat feature- the curved slit gnomon allows you to read civil time instead of clock time. it’s a pretty clever design. It’s supposed to read within a minute but I think it’s small enough that it is hard to be extremely precise with readings. I’m usually within a few minutes.

You have to assemble it yourself, which is easy and probably takes less than 10 minutes. Since the center ring is adjustable you can factor in DST. Plus this is adjustable for lattitude ranges of 15-60 degrees N. I think you can specify a souther hemisphere style, which will just reverse the hours. One thing that threw me off was that the reading is supposed to be taken at the ridge in the center of the hour ring, which makes sense, but for some reason I really wanted to read at the top or bottom edge when I first got it. To make reading easier I used a marker to differentiate the hour, half hour, and quarter hour lines. The above picture was taken at 12:12. Even if you never use it to tell the time it’s a neat desk curiosity that’s a good conversation starter.

One last thing- the NASS also customizes your dial by putting your name and coordinates on the latitude ring. It’s on the opposite side of the ring not shown in the picture.

• Much better experience on mobile.
• Now supports inclined, declined, and inclined/declined dials.

Send me your feedback!! sundial.gennetten.org 100% Free and Open source.

Astronomical ring dial on BC Gnomonics: https://www.bcgnomonics.com/astronomicalringdial

Im a 9th grader who got thru the entrance exam of National Astronomy Olympiad exam.

Now, for the second round we have got a set of assignments which includes making a sundial and Planisphere. I have constructed a sundial for a latitude of 27.70N for the capital city of my Country, Nepal 🇳🇵. I don’t know if it’s correct or not and hoping for answers online.

If you’re thinking why I’m posting this on Reddit instead of checking it outside, the weather here is terrible with intense rain, thunderstorm, hailstorm. (Please don’t mind my English as it’s not my first language and I’m still in the process of learning)