Equation of Time - Shading not displayed.

[sailingtamlin]

I have noticed that the shading is not applied to the values displayed in the Almanac for the equation of time, in situations when the value is 'negative' and should therefore be subtracted.

Although I am running the latest build, checking historical almanacs generated with older version of the code - this issue also appears to exist.

As an example, I have just generated a traditional almanac for 2025 - if I look at the daily page for 04/11/25, it displays the value for the equation of time as '16:25' - this value must be subtracted, therefore it should have a greyed out type background, however this is not displayed (neither is the value shown as a negative.

As a cross reference, the Merpass time is shown as 11:43, clearly indicating the equation of time value should be subtracted.

[aendie]

Greetings! A quick check with an official almanac verifies that the EoT times for the Sun are shaded when its Meridian Passage is after noon. As the MerPass time is rounded, 12:00 may or may not be shaded. I use the same convention for shading as in the official Nautical Almanac.

Pyalmanac is no longer maintained (with reasons that are explained on the Description page in GitHub): the Ephem astronomical library has an issue that no one solves. That's why I moved to the current astronomical library written by the same author: Skyfield. I would kindly advise you to switch to Skyalmanac using Skyfield. The same time clip as in your example from Skyalmanac is shown here (using the de421.bsp ephemeris):

I also include here the Explanation (regarding shading) from the official HMNAO Nautical Almanac for 2023:

I thank you for your concern and for reporting your problem.
The easiest link for Skyalmanac is the Python Package Index location: https://pypi.org/project/skyalmanac/

Good luck!

[sailingtamlin]

Hi There, Thanks for getting back to me so promptly, it really is much appreciated. I installed Skyalmanac this morning and re-created the Nautical Almanac for 2025 and it does indeed now show the equation of time with shading as appropriate! My apologies as my example in my initial message was wrong - I should have been referring to a date around 14/02/25, where the value of the equation of time is negative (i.e. apparent solar time/the sun is fast) and noon MST occurs before solar noon - I would highlight that Pyalmanac does not however show the shading correctly at this time (I got myself a little confused putting the example together!). Please humour me whilst I ask one question regarding the resource requirements for Skyalmanac, are they considerably higher? I struggled to get it to run on my RPi2, it was taking several hours to generate a single years Almanac, I ended up having to run it via an Ubuntu VM on my Windows based navigation PC to generate almanacs in a timely manner (still took 10-20mins). For reference, I am actually a sailor and do use these tables on a regular basis - currently mid South Atlantic bound for Brazil, its amazing what you can do with Starlink in terms of being connected, but also great to switch off,  roll back and practice the traditional navigation skills as well. Thanks Again & Best Regards Tony. *Tony Martin B. Eng (Hons) C.Eng MIET* /Engineering Consultant - Communication Systems/ /RYA Yachtmaster Ocean & Cruising Instructor/ E: ***@***.*** UK M & Whatsapp: +44 7841 689812

…

On 10/02/2025 17:21, aendie wrote: Greetings! A quick check with an official almanac verifies that the EoT times for the Sun are shaded when its Meridian Passage is after noon. As the MerPass time is rounded, 12:00 may or may not be shaded. I use the same convention for shading as in the official Nautical Almanac. Pyalmanac is no longer maintained (with reasons that are explained on the Description page in GitHub): the Ephem astronomical library has an issue that no one solves. That's why I moved to the current astronomical library written by the same author: Skyfield. I would kindly advise you to switch to Skyalmanac using Skyfield. The same time clip as in your example from Skyalmanac is shown here (using the de421.bsp ephemeris): Nov.3-5.2025.EoT.png (view on web) <https://github.com/user-attachments/assets/9e4c7f46-29f7-4da8-8843-a4f0a0439963> I also include here the Explanation (regarding shading) from the official HMNAO Nautical Almanac for 2023: 20250210_194941b.jpg (view on web) <https://github.com/user-attachments/assets/ae058e62-a18a-400c-8a50-202af793a902> I thank you for your concern and for reporting your problem. The easiest link for Skyalmanac is the Python Package Index location: https://pypi.org/project/skyalmanac/ Good luck! — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BCSDPUTKTSIOAYNJ7H54OL32PD35PAVCNFSM6AAAAABW2QQZGCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMNBZGAYTKNRQGA>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[aendie]

Greetings Tony!

Forgive me snooping up on you ... I see you made it to Recife. Well done! Wonderful yacht you have. What make & model is it? Are you traveling with RYA students? It was a bit tricky finding you as there is another British yacht named Tamlin... but that's near Glasgow.

I am very surprised that you got Skyalmanac working on a Raspberry Pi, but of course I didn't expect you to have a gaming PC on board, LOL. Pyalmanac, based on Ephem (or Pyephem) was always faster than any version that uses Skyfield, but it's less accurate too as it is based on the algorithms by Jean Meeus "Astronomical Algorithms", second edition published 1998. I did the development work on a PC with an older 8-core AMD Ryzen CPU and 32 GB of RAM. I was fed up with poor performance, so I invested time in implementing multiprocessing (I could use up to 16 threads) and found 12 threads to be quite sufficient. Hyperthreading doubles the core count such that 8 cores can handle 16 threads. But hyperthreading is "out" now as the latest generation of CPUs proves.

Let me back up a bit. I am British living in Munich, Germany. I was interested in Nautical Almanac software and detected a mistake published on thenauticalalmanac.com, which is run by "Johannes". (You'll find my name is listed in the "Disclaimer, Copyright notice and Warning" section.) He explained to me that his software, Pyalmanac for Python 2 at that time, comes from Enno Rodegerdts, a German radiologist and sailor living in Norway. He kindly offered me to take over the task of fixing it and I learned a lot about his technique of creating a file in LaTeX and then converting it into a PDF. I took over his website and converted Pyalmanac to Python version 3. Enno Rodgerdts sails SV Inua and his website is: https://sv-inua.net/the-nautical-almanac.

Pyalmanac uses a astronomical library, Ephem (= Pyephem), written by Brandon Rhodes, who at that time was genuinely unhappy with the whole concept behind it and was working on an (truly) elegant solution. His lecture from 11 years ago is entertaining even today and I recommend you to watch it: "Skyfield and 15 Years of Bad APIs - Brandon Rhodes" https://www.youtube.com/watch?v=FVEEndIwOSA

So basically I switched to providing "Johannes" with software for his website from then on. I am very fussy about accuracy and the changelog on GitHub documents all the steps I went through, which was also a learning process for me too.

You'll notice that I delved into the Lunar Distance method (extinct from around 1850 when marine chronometers became available) , which was inspired by a website that soon closed down. Jorrit Visser, an astronomer, developed it and I use his method. All my attempts to contact him failed unfortunately. Oh, and I don't own a sextant.

Currently I am implementing Planetary Phenomena charts (that show when a navigational planet is visible), an idea that I only found in one place on the internet. Rainer Lange (in Germany, also an astronomer) has published "Computation of Visibility Phenomena" here: https://www.alcyone.de/plsv/documentation/compphen.html. His planet visibility software is free but I found it very old-fashioned and limited to about 5 latitudes that he chose. My software is unpublished as I am still improving it (and testing takes ages). I cover 28 chosen latitudes between 60°S and 72°N and all years between 2000 and 2050. Do you have an email address that I could send a sample to?

I wish you fair winds and following seas. I will happily follow your sailing adventure.
Andrew Bauer

[sailingtamlin]

Hi Andrew, Thanks for getting back to me and well done for chasing us down! Our boat is Hallberg Rassy 44, easier to find on most of the tracking sites with our registered name of TamLin of Gloucester (we are part one registered, which means we must have a unique name, therefore we are 'of Gloucester' since it is our registered port in the UK). We actually left the UK back in July 2022 and are most of our way through our 3 year circumnavigation, only around 2000Nm back to the Caribbean, then a further 3,500Nm back the UK In answer to your question, we don't have students onboard (I only teach on other peoples boats), we actually generally sail two handed, just my wife and I, although I will return to professional skippering and teaching when I return to the UK. From an instructing perspective, celestial Navigation  is a bit of a passion of mine and when passaging offshore with students (or indeed with anyone else who will listen) - I do like to break out the sextant and explain/teach the basics. So by way of a by of a bit of detail on my background - its not sailing, rather it is engineering, specifically I worked in the field of satcoms & data communications in general - finally running satellite communications company for 15 years as Technical Director. As a part of this role, I was also ran the in-house software team (mostly LAMP based applications, data  transformation/routing and custom billing infrastructure) - so though I am not a developer, I have a reasonable understanding of software and now find myself writing my own code for applications onboard, mostly in python and with much support from Google to learn each new element... I have started to watch that lecture, however I need to find a quiet hour to sit down and watch fully as it immediately seems very interesting! Regarding your Planetary charts, I would certainly be interested to take a look - if you can send me a link to this address, that would be great. Finally, thanks once again for taking the time to follow up on my Emails, it is really appreciated! Best Regards Tony. *Tony Martin B. Eng (Hons) C.Eng MIET* /Engineering Consultant - Communication Systems/ /RYA Yachtmaster Ocean & Cruising Instructor/ E: ***@***.*** UK M & Whatsapp: +44 7841 689812

…

On 13/02/2025 19:26, aendie wrote: Greetings Tony! Forgive me snooping up on you ... I see you made it to Recife. Well done! Wonderful yacht you have. What make & model is it? Are you traveling with RYA students? It was a bit tricky finding you as there is another British yacht named Tamlin... but that's near Glasgow. I am very surprised that you got Skyalmanac working on a Raspberry Pi, but of course I didn't expect you to have a gaming PC on board, LOL. Pyalmanac, based on Ephem (or Pyephem) was always faster than any version that uses Skyfield, but it's less accurate too as it is based on the algorithms by Jean Meeus "Astronomical Algorithms", second edition published 1998. I did the development work on a PC with an older 8-core AMD Ryzen CPU and 32 GB of RAM. I was fed up with poor performance, so I invested time in implementing multiprocessing (I could use up to 16 threads) and found 12 threads to be quite sufficient. Hyperthreading doubles the core count such that 8 cores can handle 16 threads. But hyperthreading is "out" now as the latest generation of CPUs proves. Let me back up a bit. I am British living in Munich, Germany. I was interested in Nautical Almanac software and detected a mistake published on thenauticalalmanac.com, which is run by "Johannes". (You'll find my name is listed in the "Disclaimer, Copyright notice and Warning" section.) He explained to me that his software, Pyalmanac for Python 2 at that time, comes from Enno Rodegerdts, a German radiologist and sailor living in Norway. He kindly offered me to take over the task of fixing it and I learned a lot about his technique of creating a file in LaTeX and then converting it into a PDF. I took over his website and converted Pyalmanac to Python version 3. Enno Rodgerdts sails SV Inua and his website is: https://sv-inua.net/the-nautical-almanac. Pyalmanac uses a astronomical library, Ephem (= Pyephem), written by Brandon Rhodes, who at that time was genuinely unhappy with the whole concept behind it and was working on an (truly) elegant solution. His lecture from 11 years ago is entertaining even today and I recommend you to watch it: "Skyfield and 15 Years of Bad APIs - Brandon Rhodes" https://www.youtube.com/watch?v=FVEEndIwOSA So basically I switched to providing "Johannes" with software for his website from then on. I am very fussy about accuracy and the changelog on GitHub documents all the steps I went through, which was also a learning process for me too. You'll notice that I delved into the Lunar Distance method (extinct from around 1850 when marine chronometers became available) , which was inspired by a website that soon closed down. Jorrit Visser, an astronomer, developed it and I use his method. All my attempts to contact him failed unfortunately. Oh, and I don't own a sextant. Currently I am implementing Planetary Phenomena charts (that show when a navigational planet is visible), an idea that I only found in one place on the internet. Rainer Lange (in Germany, also an astronomer) has published "Computation of Visibility Phenomena" here: https://www.alcyone.de/plsv/documentation/compphen.html. His planet visibility software is free but I found it very old-fashioned and limited to about 5 latitudes that he chose. My software is unpublished as I am still improving it (and testing takes ages). I cover 28 chosen latitudes between 60°S and 72°N and all years between 2000 and 2050. Do you have an email address that I could send a sample to? I wish you fair winds and following seas. I will happily follow your sailing adventure. Andrew Bauer — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BCSDPUQBRR4XSKULW4TWLS32PUEXRAVCNFSM6AAAAABW2QQZGCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMNJXG42DGMZXGA>. You are receiving this because you authored the thread.Message ID: ***@***.***> aendie*aendie* left a comment (rodegerdts/Pyalmanac#3) <#3 (comment)> Greetings Tony! Forgive me snooping up on you ... I see you made it to Recife. Well done! Wonderful yacht you have. What make & model is it? Are you traveling with RYA students? It was a bit tricky finding you as there is another British yacht named Tamlin... but that's near Glasgow. I am very surprised that you got Skyalmanac working on a Raspberry Pi, but of course I didn't expect you to have a gaming PC on board, LOL. Pyalmanac, based on Ephem (or Pyephem) was always faster than any version that uses Skyfield, but it's less accurate too as it is based on the algorithms by Jean Meeus "Astronomical Algorithms", second edition published 1998. I did the development work on a PC with an older 8-core AMD Ryzen CPU and 32 GB of RAM. I was fed up with poor performance, so I invested time in implementing multiprocessing (I could use up to 16 threads) and found 12 threads to be quite sufficient. Hyperthreading doubles the core count such that 8 cores can handle 16 threads. But hyperthreading is "out" now as the latest generation of CPUs proves. Let me back up a bit. I am British living in Munich, Germany. I was interested in Nautical Almanac software and detected a mistake published on thenauticalalmanac.com, which is run by "Johannes". (You'll find my name is listed in the "Disclaimer, Copyright notice and Warning" section.) He explained to me that his software, Pyalmanac for Python 2 at that time, comes from Enno Rodegerdts, a German radiologist and sailor living in Norway. He kindly offered me to take over the task of fixing it and I learned a lot about his technique of creating a file in LaTeX and then converting it into a PDF. I took over his website and converted Pyalmanac to Python version 3. Enno Rodgerdts sails SV Inua and his website is: https://sv-inua.net/the-nautical-almanac. Pyalmanac uses a astronomical library, Ephem (= Pyephem), written by Brandon Rhodes, who at that time was genuinely unhappy with the whole concept behind it and was working on an (truly) elegant solution. His lecture from 11 years ago is entertaining even today and I recommend you to watch it: "Skyfield and 15 Years of Bad APIs - Brandon Rhodes" https://www.youtube.com/watch?v=FVEEndIwOSA So basically I switched to providing "Johannes" with software for his website from then on. I am very fussy about accuracy and the changelog on GitHub documents all the steps I went through, which was also a learning process for me too. You'll notice that I delved into the Lunar Distance method (extinct from around 1850 when marine chronometers became available) , which was inspired by a website that soon closed down. Jorrit Visser, an astronomer, developed it and I use his method. All my attempts to contact him failed unfortunately. Oh, and I don't own a sextant. Currently I am implementing Planetary Phenomena charts (that show when a navigational planet is visible), an idea that I only found in one place on the internet. Rainer Lange (in Germany, also an astronomer) has published "Computation of Visibility Phenomena" here: https://www.alcyone.de/plsv/documentation/compphen.html. His planet visibility software is free but I found it very old-fashioned and limited to about 5 latitudes that he chose. My software is unpublished as I am still improving it (and testing takes ages). I cover 28 chosen latitudes between 60°S and 72°N and all years between 2000 and 2050. Do you have an email address that I could send a sample to? I wish you fair winds and following seas. I will happily follow your sailing adventure. Andrew Bauer — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BCSDPUQBRR4XSKULW4TWLS32PUEXRAVCNFSM6AAAAABW2QQZGCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDMNJXG42DGMZXGA>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[aendie]

Greetings, Tony .... and I appreciate the explanations you gave above.

I made the charts for 08°S. Around the equator they look rather boring. At higher latitudes, say above 60°N, they begin to look interesting. Here they are. The text on the first page in mine and could do with some improvements, I guess.

Mercury(A4)_08.0S_2025.pdf

Venus(A4)_08.0S_2025.pdf

Mars(A4)_08.0S_2025.pdf

Jupiter(A4)_08.0S_2025.pdf

Saturn(A4)_08.0S_2025.pdf

A Hallberg-Rassy 44 Center Cockpit ... my dream yacht. Enno Rodegerdts, author of Pyalmanac and living in Norway also upgraded to a Hallberg-Rassy 43 - around February 2020. He posts lots of lovely pictures occasionally (if you subscribe to his newsletters) but it's all written in German.

This is just before he bought it.

Now and then I follow Sailing Yacht Florence (in their Oyster). I always enjoy an update from The O'Kellys - buying a yacht is a pain, but they are very knowledgeable. A recent discovery of mine is Salt & Light Dix470 (building his catamaran with wood in Japan). I used to send my Nautical Almanacs to Kraken Yachts, but they're so busy and never commented. I ask myself if you have ever met well-known yachting YouTubers on your cruise.

By the way, I have had contact with HMNAO - they thanked me for a trivial mistake I found. I think I have another one for them, but currently I'm not in the mood to document my niggles.

I looked for a book (in German) that I once read ... I can't find it. Before taking up a permanent job, a young guy sailed solo to the States and then decided to ship his yacht back on a cargo vessel. He had a cabin on that vessel too. Little did he know that the friendly captain used a sextant as a hobby, and got him calculating like mad on his return journey. The captain also knew the sky like the back of his hand.

Looking forward to your next update.

Andrew

[aendie]

Fair winds and following seas on the next leg of your journey!
More news from me to follow in a couple of days :-)
Kind Regards, Andrew

[aendie]

Greetings Tony!

It appears you are about 28°N, so I would like to send you my planet visibility charts for 30°N (which are close enough). I'd rather call them Planet Invisibility charts as they tell you when you definitely cannot see a planet because it is below the horizon, and when you probably cannot see it as the sun is higher than 6 degrees below the horizon, i.e. it's too bright.

Also the times I quote here are based on the middle of your current time zone ... take 60°W as an example. So if you're 7.5° higher or lower than 60°W (a time zone is 15° wide), add or subtract 30 minutes to the time when it is visible. Dawn and Dusk refer to Nautical Dawn and Dusk below.

Venus(A4)_30.0N_2025.pdf

You see in mid-May that Venus rises just before 03:00 and is visible till dawn about 04:40 when the sky brightens.

Mars(A4)_30.0N_2025.pdf

Mid-May Mars will be visible at dusk around 19:00 and it should be visible till about 23:45 when it sets. Mars is at its highest (= Meridian Passage) around 17:30.

Jupiter(A4)_30.0N_2025.pdf

Jupiter is visible mid-May from dusk about 17:45 to 19:00 when it sets (obviously at your horizon). It's way past its Meridian Passage, so it will be low in the sky anyway.

Saturn(A4)_30.0N_2025.pdf

Saturn will be visible from 02:30 in the morning when it rises, till dawn about 04:45, still low in the sky. You see that by mid-June it rises earlier at 00:30 although dawn has only crept to 04:30, so the visibility window has widened.

Venus is obviously the brightest at -4.0; Mars is dimmer at roughly -1.3; Jupiter is in-between at roughly -2.4; Saturn will be difficult to see at approximately +0.6 to +0.9 brightness.

I wish you a safe and enjoyable trip. And safety comes first as you well know - so please don't be distracted too long with navigation by planets. Their position you should be able to get using 'skyalmanac'.

Of course I'd be glad to hear from you, even if it's just to say your cup of coffee is delightful.

Oh, and I just walked 126 km in Spain from Sarria to Santiago de Compostela along the famous Camino Francés. I took 9 days to walk it slowly, joined by my daughter.

Kind Regards from Munich.
Andrew

[sailingtamlin]

Hi Andrew, Thanks for sending these through, we are currently passaging up to Bermuda and will then be headed across to the Azores, so should have plenty of time to take a proper look at these charts and have a bash at some planet spotting along the way- Actually its really useful to have information as to what we should be able to see at dawn/dusk as we can then use them to take position sights! Will let you know how we get on, oh and being very typically English we largely drink tea onboard - ideally in copious quantities! Best Regards Tony. *Tony Martin B. Eng (Hons) C.Eng MIET* /Engineering Consultant - Communication Systems/ /RYA Yachtmaster Ocean & Cruising Instructor/ E: ***@***.*** UK M & Whatsapp: +44 7841 689812

…

On 14/05/2025 15:44, aendie wrote: *aendie* left a comment (rodegerdts/Pyalmanac#3) <#3 (comment)> Greetings Tony! It appears you are about 28°N, so I would like to send you my planet visibility charts for 30°N (which are close enough). I'd rather call them Planet Invisibility charts as they tell you when you definitely cannot see a planet because it is below the horizon, and when you probably cannot see it as the sun is high than 6 degrees below the horizon, i.e. it's too bright. Also the times I quote here are based on the middle of your current time zone ... take 60°W as an example. So if you're 7.5° higher or lower than 60°W (a time zone is 15° wide), add or subtract 30 minutes to the time when it is visible. Dawn and Dusk refer to Nautical Dawn and Dusk below. Venus(A4)_30.0N_2025.pdf <https://github.com/user-attachments/files/20213066/Venus.A4._30.0N_2025.pdf> You see in mid-May that Venus rises just before 03:00 and is visible till dawn about 04:40 when the sky brightens. Mars(A4)_30.0N_2025.pdf <https://github.com/user-attachments/files/20213115/Mars.A4._30.0N_2025.pdf> Mid-May Mars will be visible at dusk around 19:00 and it should be visible till about 23:45 when it sets. Mars is at its highest (= Meridian Passage) around 17:30. Jupiter(A4)_30.0N_2025.pdf <https://github.com/user-attachments/files/20213189/Jupiter.A4._30.0N_2025.pdf> Jupiter is visible mid-May from dusk about 17:45 to 19:00 when it sets (obviously at your horizon). It's way past its Meridian Passage, so it will be low in the sky anyway. Saturn(A4)_30.0N_2025.pdf <https://github.com/user-attachments/files/20213226/Saturn.A4._30.0N_2025.pdf> Saturn will be visible from 02:30 in the morning when it rises, till dawn about 04:45, still low in the sky. You see that by mid-June it rises earlier at 00:30 although dawn has only crept to 04:30, so the visibility window has widened. Venus is obviously the brightest at -4.0; Mars is dimmer at roughly -1.3; Jupiter is in-between at roughly -2.4; Saturn will be difficult to see at approximately +0.6 to +0.9 brightness. I wish you a safe and enjoyable trip. And safety comes first as you well know - so please don't be distracted too long with navigation by planets. Their position you should be able to get using 'skyalmanac'. Of course I'd be glad to hear from you, even if it's just to say your cup of coffee is delightful. Oh, and I just walked 126 km in Spain from Sarria to Santiago de Compostela along the famous Camino Francés. I took 9 days to walk it slowly, joined by my daughter. Kind Regards from Munich. Andrew — Reply to this email directly, view it on GitHub <#3 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BCSDPURSZZTVJFAWGF7OHAD26OMJ7AVCNFSM6AAAAABW2QQZGCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQOBRGM3DCNBSGU>. You are receiving this because you authored the thread.Message ID: ***@***.***>