f68r: eclipse from 1419?

[Linda]

I'm not sure you have provided a single medieval example of a table of eclipses from Europe? Ordinary planetary charts are not enough to compute the eclipses, this requires some advanced computation not available before the XVIII century or some historical records and application of the saros cycles.

I don't think there is any evidence so far that in the XV century Europe:
1) there was a known way to precompute eclipse months (and thus dates) for all solar eclipses regardless of their geographic location 
2) invisible eclipses (those that were only visible outside of Europe or other places of interest) were considered important for astrology

Unless there are direct quotes from any medieval sources to the contrary, I don't think we can assume these above are true.

It appears it was possible. I got this from Gemini:

Mnemonic and Diagrammatic Charts
In medieval manuscripts, eclipse diagrams (rotae or tables) were often used to illustrate the underlying geometry of the universe rather than just serve as a practical night-by-night weather forecast. Because these tables were pedagogical, they included theoretical eclipse points along the Saros or Metonic cycles regardless of local visibility.

Why Astronomers Calculated Them

1. Checking Mathematical Consistency: Computing non-visible eclipses was the ultimate test of an astronomical table's underlying geometric model (such as Ptolemy’s Almagest). If a table skipped non-visible eclipses, the mathematical cycles would break.
   
2. Long-Distance Calibration: Astronomers knew Earth was round and that time differed by longitude. Knowing that an eclipse occurred at a specific time—even if below the local horizon—allowed scholars to cross-reference observations sent by correspondents in Persia, India, or North Africa to measure differences in terrestrial longitude.
   

The raw astronomical calculations for syzygy (mean and true conjunction) yielded a real eclipse event. In a full set of ephemerides generated for 1419, this entry would either be flagged as occurring sub terra (below the earth) or listed with zero local magnitude.

Anyone using tables based on Paris, Toledo, or Oxford meridians to calculate upcoming conjunctions for 1419 would produce mathematical parameters showing a valid solar eclipse at syzygy. However, applying the standard medieval tables for solar parallax (parallaxis lunae) would reveal that, from European latitudes, the Moon’s apparent disc shifted completely clear of the Sun's disc.

By 1419, early 15th-century astronomers (particularly in places like Vienna, Prague, and Oxford) were heavily focused on refining lunar-solar tables:

Johannes von Gmunden (a pioneer of the Vienna School of Mathematics/Astronomy) was actively compiling and re-calculating astronomical tables and eclipse ephemerides around 1415–1425.

Prophatius Judaeus’ and John of Linières’ auxiliary tables were widely copied in manuscripts at this exact time to streamline calculating whether a syzygy was a visible or invisible eclipse.

When medieval computers calculated 1419, they routinely worked through the math for syzygies regardless of local night/day or parallax, meaning the numbers for non-visible eclipses like those of 1419 were recorded in their working notebooks and master tables before being filtered out for practical local calendars.

In late medieval astronomy, these appeared in three distinct formats depending on who compiled the manuscript and how far they carried the calculations:

1. Comprehensive Master Tables (Tabulae Syzygiarum)
In master computing tables derived from the Alfonsine Tables—such as those produced by Johannes von Gmunden in Vienna around 1415–1420—every single mean and true syzygy (conjunction) was calculated mathematically.

In these master reference tables:

The conjunction for March 26, 1419 and September 19, 1419 would appear in the chronological ledger of true solar-lunar conjunctions.

They included calculated parameters such as the true position of the Sun and Moon, the argument of latitude, and the distance to the Moon's nodes (Ω). Because the angular distance to the node fell within the "eclipse boundary" (≈106
′
−110
′
  for solar eclipses), the table mathematically flagged the conjunction as a valid eclipse event.

2. Ephemerides & Almanacs (With Parallax Adjustments)
When an astronomer moved from master astronomical tables to compiling a practical almanac (a year-by-year ephemeris for local use in Oxford, Paris, or Prague), they applied the local parallax tables (parallaxis lunae).

When applying European latitude coordinates to the 1419 events, two things happened in the manuscript tables:

The September 19, 1419 Eclipse: The calculated time of true conjunction fell during night hours for European longitudes. In full eclipse lists, it would be explicitly written in Latin as sub terra ("below the earth" / invisible).

The March 26, 1419 Eclipse: The parallax calculation showed that from European latitudes, the Moon’s apparent displacement shifted its disc out of alignment with the Sun. Manuscripts handling this either noted the eclipse magnitude as 0 digits (0 digiti—meaning non-visible locally) or listed the event alongside a notation like non apparebit in his regionibus ("will not appear in these regions").

3. Geographical Coordinate & Shadow Tables
Because Islamic and Late Medieval European astronomy accounted for long-distance geographical differences, master tables often included auxiliary tables for different climate zones (climata).

If a 15th-century scholar recalculated the March 26, 1419 eclipse for meridians further east or south (such as Cairo, Baghdad, or Mecca), the tables yielded a positive eclipse magnitude (partial/annular visibility), proving that while invisible to Central Europe, the eclipse was physically real.