Quote:The Black Hour (1433 CE)
One of the most celebrated eclipses in the Middle Ages was called the "Black Hour". It happened in Scotland and it has been said that darkness came about 3 pm on June 17, 1433 CE, and was very deep.

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Coronica zo Collen Wrote:zu dem selven jair, 8 tage vur sent Johans dage mitzsomer, des abendtz na der veirder uren, do hadde men dat schoinste herlichtste eclipsis dat man je geschach. ind it wart dunkel over alle werelt, ind man insach gein licht.

In the same year, 8 days before St.John’s day of the solstice, in the evening at the fourth hour, there was the most beautiful and most magnificent eclipse ever happened. And it was dark over all world, and one could see no light.

(26-07-2026, 09:54 PM)oshfdk Wrote: You are not allowed to view links. Register or Login to view.I'm not sure if the table is about future eclipses or the record of past eclipses? It starts with 1406 and ends somehow abruptly with the year of 1462

(27-07-2026, 07:45 PM)Jorge_Stolfi Wrote: You are not allowed to view links. Register or Login to view.Predictions based on periodicity are necessarily wrong in the long term, because the astronomical periods are not commensurate.  Thus  it would not be useful to make them for more than a few decades into the future.  No?

(27-07-2026, 09:40 PM)denty Wrote: You are not allowed to view links. Register or Login to view.Summary Table of the Medieval Workflow for Calculating an Eclipse from the Toledo Tables:

Step                                               Purpose                                      Toledo Tables Used

1. Mean syzygy                                Identify candidate eclipse             Mean motions
2. Equations of center                       Correct Sun/Moon positions          Solar & lunar anomaly tables
3. True syzygy                                  Exact conjunction/opposition        Mean motions + corrections
4. Lunar latitude                               Determine if eclipse possible         Latitude tables
5. Parallax                                        Local visibility                             Parallax tables
6. Magnitude                                    Size of eclipse                             Radii tables
7. Local circumstances                       Local timing                                Longitude/time tables

(27-07-2026, 08:36 PM)oshfdk Wrote: You are not allowed to view links. Register or Login to view.I'm not even sure what method they would use to observe partial eclipses, was camera obscura known in Europe at the time?

(28-07-2026, 10:23 AM)Jorge_Stolfi Wrote: You are not allowed to view links. Register or Login to view.

(27-07-2026, 09:40 PM)denty Wrote: You are not allowed to view links. Register or Login to view.Summary Table of the Medieval Workflow for Calculating an Eclipse from the Toledo Tables:

Step                                               Purpose                                      Toledo Tables Used

1. Mean syzygy                                Identify candidate eclipse             Mean motions
2. Equations of center                       Correct Sun/Moon positions          Solar & lunar anomaly tables
3. True syzygy                                  Exact conjunction/opposition        Mean motions + corrections
4. Lunar latitude                               Determine if eclipse possible         Latitude tables
5. Parallax                                        Local visibility                             Parallax tables
6. Magnitude                                    Size of eclipse                             Radii tables
7. Local circumstances                       Local timing                                Longitude/time tables

Thanks!   So, from that "workflow", I would guess that they could predict quite accurately when the next eclipse would occur; but the errors in the tables would cause prediction to fail beyond a certain point because the three bodies would not be sufficiently aligned on that date and/or the path of the eclipse would be inaccessible.  

That is, the eclipse would not happen, but the non-happening would happen precisely when predicted. 

Makes sense?

All the best, --stolfi

(28-07-2026, 10:51 AM)Jorge_Stolfi Wrote: You are not allowed to view links. Register or Login to view.

(27-07-2026, 08:36 PM)oshfdk Wrote: You are not allowed to view links. Register or Login to view.I'm not even sure what method they would use to observe partial eclipses, was camera obscura known in Europe at the time?

During a partial eclipse the shadows of trees become quite remarkable: the white spots created by small gaps between leaves become crescent-shaped instead of circular.  

If that was not enough by itself, it should have inspired many to build their camera oscura.   All they needed was a small hole on the roof and a piece of paper on the floor.

Quote:Aristotle is also thought to have used camera obscura for observing solar eclipses.[18] The formation of pinhole images is touched upon as a subject in the work Problems – Book XV, asking:

Why is it that when the sun passes through quadri-laterals, as for instance in wickerwork, it does not produce a figure rectangular in shape but circular?

and further on:

Why is it that an eclipse of the sun, if one looks at it through a sieve or through leaves, such as a plane-tree or other broadleaved tree, or if one joins the fingers of one hand over the fingers of the other, the rays are crescent-shaped where they reach the earth? Is it for the same reason as that when light shines through a rectangular peep-hole, it appears circular in the form of a cone?