1020

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Communication

Alhazen (Ibn al-Haytham) describes the camera obscura: a real image is projected into a darkened box. The image can be viewed from inside the box or can be projected onto ground glass to be seen from outside the box. Alhazen reports that he did not discover this device. See also 1553 Communication.

In Mizan al-hikma ("on the balance of wisdom") Alhazen discusses how the atmosphere refracts light and uses the onset of twilight as a means to make an estimate of the height of the atmosphere.

Alhazen solves several problems from what is now called number theory involving remainders (equivalent to congruence for numbers) and perfect numbers (a number is perfect if the sum of its factors is the number). He also writes on using lunes for squaring the circle, but may not have realized that this method will not work. See also 100 Mathematics; 1801 Mathematics.

Alhazen determines that light travels from objects to the eye, emanating from some bodies and being reflected from others, and determines laws of reflection in curved mirrors. These laws enable him to explain correctly how lenses work and to describe focusing by parabolic mirrors, such as those used in today's reflecting telescopes. His optical work Kitab al-manazir ("treasury of optics") is influential in Europe after translation into Latin as Opticae thesaurus Alhazeni in 1572. See also 140 ce Physics; 1270 Physics.

This article is about the year 1020. For the number (and other uses), see 1020 (number).

Millennium:	2nd millennium
Centuries:	10th century – 11th century – 12th century
Decades:	990s  1000s  1010s  – 1020s –  1030s  1040s  1050s
Years:	1017 1018 1019 – 1020 – 1021 1022 1023

1020 by topic

Lists of leaders

State leaders

Birth and death categories

Births – Deaths

Establishments and disestablishments categories

Establishments – Disestablishments

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1020 in other calendars

Gregorian calendar	1020 MXX
Ab urbe condita	1773
Armenian calendar	469 ԹՎ ՆԿԹ
Assyrian calendar	5770
Bahá'í calendar	-824–-823
Bengali calendar	427
Berber calendar	1970
English Regnal year	N/A
Buddhist calendar	1564
Burmese calendar	382
Byzantine calendar	6528–6529
Chinese calendar	己未年十二月初四日 (3656/3716-12-4) — to — 庚申年十二月十五日 (3657/3717-12-15)
Coptic calendar	736–737
Ethiopian calendar	1012–1013
Hebrew calendar	4780–4781
Hindu calendars
- Vikram Samvat	1076–1077
- Shaka Samvat	942–943
- Kali Yuga	4121–4122
Holocene calendar	11020
Iranian calendar	398–399
Islamic calendar	410–411
Japanese calendar
Korean calendar	3353
Minguo calendar	892 before ROC 民前892年
Thai solar calendar	1563
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Year 1020 (MXX) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar.

Events

By place

Asia

• Goryeo and the Liao Dynasty exchange embassies following a seven-year territorial dispute.
• The massive Kandariya Mahadeva Hindu Temple is completed in the Chandela capital of Khajuraho.

Europe

• The city of Saint-Germain-en-Laye is founded.
• Henry II of Germany conducts his third Italian military campaign .
• Canute the Great codifies the laws of England.

Births

• Zhang Zai, Song Dynasty Chinese Neo-Confucian philosopher and cosmologist (d. 1077)
• Su Song, famous Song Dynasty Chinese scientist and engineer (d. 1101)

Deaths

• June 12 – Lyfing, Archbishop of Canterbury
• Ferdowsi Tousi, Persian epic poet (b. 935)
• Leif Ericson, Icelandic explorer
• Fan Kuan, Chinese landscape painter

References

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