astronomy

Sahl ibn Bishr

Sahl ibn Bishr is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sahl ibn Bishr rather than just read about it. In short: Sahl ibn Bishr al-Israili (c. 786 – c. 845) was a Jewish or Syriac Christian astrologer, astronomer and mathematician from Tabaristan. He was the father of Ali ibn Sahl the scientist and physician, who became a convert to Islam.

Key takeaways

Sahl ibn Bishr belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sahl ibn Bishr to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sahl ibn Bishr from memory before moving on to harder problems.

Reference excerpt

Sahl ibn Bishr al-Israili (c. 786 – c. 845) was a Jewish or Syriac Christian astrologer, astronomer and mathematician from Tabaristan. He was the father of Ali ibn Sahl the scientist and physician, who became a convert to Islam. He served as astrologer to the governor of Khuristan and then to the vizier of Baghdad. He wrote books on astronomy, astrology, and arithmetic, all in Arabic.

His works Sahl is believed to be the first who translated the Almagest of Ptolemy into Arabic. Sahl ibn Bishr wrote in the Greek astrological tradition. Sahl's first five books were preserved in the translation of John of Seville (Johannes Hispanus) (c. 1090 – c. 1150). See the English translation The Introduction to the Science of the Judgments of the Stars. Translated by James Herschel Holden (Tempe, Az.: A.F.A., Inc., 2008)ix, 213 pp. The sixth book deals with three thematic topics regarding the influences on the world and its inhabitants was translated by Herman of Carinthia. The work contains divinations based on the movements of the planets and comets. Books by Sahl ibn Bishr in Arabic include:

Ahkam fi al-Nujum (Laws of the Astrology) Kitab al-ikhtiyarat 'ala al-buyut al-ithnai 'ashar (Book of elections according to the twelve houses). al-Masa'il al-Nujumiyah (The astrological problems)

Notes

References

Worked examples

Example 1 — a first encounter with Sahl ibn Bishr

Start with the simplest possible case. Write down what Sahl ibn Bishr claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sahl ibn Bishr before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sahl ibn Bishr ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sahl ibn Bishr

In research: Sahl ibn Bishr appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sahl ibn Bishr in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sahl ibn Bishr is common in secondary-school and first-year university syllabi. It links to neighbouring topics 780s births, 845 deaths, 9th-century Iranian astronomers, so understanding it makes those chapters shorter.
In everyday life: Look for Sahl ibn Bishr outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sahl ibn Bishr in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sahl ibn Bishr means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sahl ibn Bishr out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sahl ibn Bishr in simple terms?

Why does Sahl ibn Bishr matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sahl ibn Bishr?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sahl ibn Bishr.