Aloysius Lilius (ca. 1510 – 1576), also variously referred to as Luigi Lilio, Luigi Giglio, was an Italian doctor, astronomer, philosopher and chronologist, and also the "primary author" who provided the proposal that (after modifications) became the basis of the Gregorian Calendar reform of 1582.
Life and work 
Not much is known about the early life of Lilius/Lilio/Giglio. It is known that he came from Calabria, Italy, from Cirò (or Zirò). He studied medicine and astronomy in Naples, after which he served Earl Carafa. He settled in Verona and died in 1576. Although he was still alive at the time when his proposal was presented at Rome, it does not seem that he made the presentation; it was handled by his brother Antonio, also a physician and astronomer.
He is primarily known as the "first author" of the Gregorian Calendar: he wrote the proposal on which (after modifications) the calendar reform was based. Lilio's brother Antonio presented the manuscript to Pope Gregory XIII; it was passed to the calendar reform commission in 1575. The commission issued a printed summary entitled Compendium novae rationis restituendi kalendarium (Compendium of a New Plan for the Restitution of the Calendar), printed in 1577 and circulated within the Roman Catholic world in early 1578 as a consultation document. Lilio's manuscript itself is not known to have survived; the printed 'Compendium' is the nearest known source for the details it contained.
The processes of consultation and deliberation meant that the reform to the calendar did not occur until 1582, six years after the death of Luigi Lilio in 1576. The reform had by then received some modifications in points of detail by the reform commission, in which one of the leading members was Clavius, who afterwards wrote defences and an explanation of the reformed calendar, including an emphatic acknowledgement of Lilio's work, especially for his provision of a useful reform for the lunar cycle: "We owe much gratitude and praise to Luigi Giglio who contrived such an ingenious Cycle of Epacts which, inserted in the calendar, always shows the new moon and so can be easily adapted to any length of the year, if only at the right moments the due adjustment is applied." The papal bull (Inter gravissimas) was issued on 24 February 1582, ordering Catholic clergy to adopt the new calendar, and exhorting Catholic sovereigns to do the same.
The year 2010 is the 500th year since the Lilius' birth; several activities have been organized (by Italian astronomers) in order to recognize the great work performed by him. In particular, in Torretta di Crucoli (Crotone, Italy), a new astronomical group has been created and dedicated to Luigi Lilio: Circolo Astrofili Luigi Lilio Torretta (C.A.L.L.T.)
See also 
- For name-variants and a few biographical details (including citation to a biography published in 1963) see page 206 in: A Ziggelaar (1983), "The papal bull of 1582 promulgating a reform of the calendar", pages 201-239 in G.V. Coyne (ed.), The Gregorian Reform of the Calendar: Proceedings of the Vatican conference to commemorate its 400th anniversary (Vatican City: Specola Vaticana), 1983.
- "Friday the 13th and the Mathematics of the Gregorian Calendar," Richard W. Beveridge, University of Maine, webpage: Bev-2003.
- Lilio was said to have lectured in medicine at the University of Perugia from 1552, but the source for that was recently checked by A Ziggelaar, who could not find verification: A Ziggelaar (1983), article cited above, at page 233, footnote 22.
- A biography (in Italian) by Giulio Aromolo (Napoli, 1963, Istituto della stampa, 109pp), "Papi astronomi e patte : Luigi Giglio astronomo 'primus auctor' della riforma gregoriana del calendario", is referenced by A Ziggelaar (1983) in the article cited above, at page 223, footnote 21.
- According to A Ziggelaar (1983), article cited above, see page 208.
- G Moyer (1983), "Aloisius Lilius and the 'Compendium novae rationis restituendi kalendarium'", pages 171-188 in G.V. Coyne (ed.), The Gregorian Reform of the Calendar: Proceedings of the Vatican conference to commemorate its 400th anniversary (Vatican City: Specola Vaticana), 1983.
- The 'Compendium' text can be found (in Latin) as part of Christopher Clavius' complete explanation of the Gregorian calendar, in Volume 5 of Clavius' complete mathematical works, online from Mathematics Library, University of Notre Dame, from page 3 to page 12. An html version (in Latin with a French translation) is also available here.
- A Ziggelaar (1983), article cited above, see page 209.
- Moyer, G. (1982 November). "Luigi Lilio and the Gregorian reform of the calendar". Sky and Telescope 64 (11): 418–9. Bibcode:1982S&T....64..418M..
- Bond, J.J. (1966). Handy Book of Rules and Tables for Verifying Dates within the Christian Era. Russell & Russell, a Division of Atheneum House Inc..
- Encyclopædia Britannica. Chicago: Encyclopædia Britannica, Inc. 1980. p. 602..
- "Aloisius Lilius". Catholic Encyclopedia. New York: Robert Appleton Company. 1913.
- Circolo Astrofili Luigi Lilio Torretta