astronomy

Gros Horloge

Gros Horloge 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 Gros Horloge rather than just read about it. In short: The Gros-Horloge (English: Great Clock) is an astronomical clock from the 14th century in Rouen, Normandy. The clock is installed in a Renaissance arch crossing the Rue du Gros-Horloge.

Key takeaways

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

Reference excerpt

The Gros-Horloge (English: Great Clock) is an astronomical clock from the 14th century in Rouen, Normandy. The clock is installed in a Renaissance arch crossing the Rue du Gros-Horloge. The mechanism is one of the oldest in France, the movement having been made in 1389. Construction of the clock was started by Jourdain del Leche who lacked the necessary expertise to finish the task, so the work was completed by Jean de Felain, who became the first to hold the position of governor of the clock. The clock was originally constructed without a dial, with one revolution of the hour-hand representing twenty-four hours. The movement is cast in wrought iron, and at approximately twice the size of the Wells Cathedral clock, it is perhaps the largest such mechanism still extant. A facade was added in 1529 when the clock was moved to its current position. The mechanism was electrified in the 1920s and it was restored in 1997. As of 17 September 2025, the clock movement itself is fully functional. There is an electrical solenoid that rings one of the two bells in the tower on the 1/4 hr.

The Renaissance facade represents a golden sun with 24 rays on a starry blue background. The dial measures 2.5 metres (25 dm; 250 cm) in diameter. The phases of the moon are shown in the oculus of the upper part of the dial. It completes a full rotation in 29 days. The week days are shown in an opening at the base of the dial with allegorical subjects for each day of the week. The Gros Horloge has featured in paintings by J. M. W. Turner and the French impressionist Léon-Jules Lemaître.

References

Illustrations

Worked examples

Example 1 — a first encounter with Gros Horloge

Start with the simplest possible case. Write down what Gros Horloge 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 Gros Horloge 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 Gros Horloge 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 Gros Horloge

In research: Gros Horloge 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 Gros Horloge 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: Gros Horloge is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical clocks in France, Rouen, so understanding it makes those chapters shorter.
In everyday life: Look for Gros Horloge 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 Gros Horloge in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gros Horloge 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 Gros Horloge out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gros Horloge in simple terms?

The Gros-Horloge (English: Great Clock) is an astronomical clock from the 14th century in Rouen, Normandy. The clock is installed in a Renaissance arch crossing the Rue du Gros-Horloge.

Why does Gros Horloge 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 Gros Horloge?

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 Gros Horloge.