science

Greenwich 28-inch refractor

Greenwich 28-inch refractor is a science 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 Greenwich 28-inch refractor rather than just read about it. In short: The Greenwich 28-inch refractor is a telescope at the Royal Observatory, Greenwich, where it was first installed in 1893. It is a 28-inch ( 71 cm) aperture objective lens telescope, otherwise known as a refractor, and was made by the telescope maker Sir Howard Grubb.

Key takeaways

Greenwich 28-inch refractor belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Greenwich 28-inch refractor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Greenwich 28-inch refractor from memory before moving on to harder problems.

Reference excerpt

The Greenwich 28-inch refractor is a telescope at the Royal Observatory, Greenwich, where it was first installed in 1893. It is a 28-inch ( 71 cm) aperture objective lens telescope, otherwise known as a refractor, and was made by the telescope maker Sir Howard Grubb. The achromatic lens was made Grubb from Chance Brothers glass. The mounting is older however and dates to the 1850s, having been designed by Royal Observatory director George Airy and the firm Ransomes and Simms. The telescope is noted for its spherical dome which extends beyond the tower, nicknamed the "onion" dome. Another name for this telescope is "The Great Equatorial" which it shares with the building, which housed an older but smaller telescope previously. The telescope was re-commissioned by Queen Elizabeth II in May 1975 after it was brought back from Herstmonceux in Sussex. It was placed in the renovated original dome at Greenwich for the tricentennial celebration of the observatory.

History

A 28-inch aperture refractor was ordered from the telescope maker Grubb in 1885. It was installed by 1893 in the Great Equatorial building. The 28-inch telescope was installed on the same mounting as an older 12.8 inch aperture refractor at the same location. The 12.8 inch was moved to be a guide telescope for the Thompson 26-inch refractor. The mounting dates to the 1850s. The mounting is an English equatorial mount built by Ransomes and Sims, and Williams Sims. The dome's overall design dates to 1892 but the current dome is made of fibreglass and dates to 1971, after the original made of iron and papier-mâché was in need of refurbishment when the telescope was moved back to Greenwich in the 1970s. The telescope is reported to have a resolving power of 0.16 arcseconds. The telescope's objective lens was removed during the Second World War for safekeeping, and then put back after that conflict was over. The 28-inch was moved to Herstmonceux in 1947, and operated there between 1957 and 1970, but was moved back to Greenwich in 1971. The return of the 28-inch refractor in 1971 to the Greenwich Observatory site was featured in an episode of the British television show The Sky at Night. One reason for this was to have it ready for the tricentennial of Greenwich Observatory in 1975. The telescope was recommissioned by Queen Elizabeth II in May 1975 after it was brought back from Herstmonceux. Since that time it has been under care of the National Maritime Museum, where it is noted as one of the most popular exhibits. The original site dates to King Charles II's commissioning of John Flamsteed to be an astronomical observer on March 4, 1675; by the summer of 1676 Flamsteed operated from the new Flamsteed House on Greenwich hill. The telescope is known as the largest aperture refractor in the United Kingdom, and is a popular tourist attraction. The telescope now features in observing events in the 21st century. In the 1980s it was noted that there was an admission charge for visitors to look through the 28-inch. The guide telescope for the 28-inch Grubb as of the 1890s was the Corbett telescope with 6.5 inch aperture refractor. The 6.5 inch aperture Corbett telescope had also been used as a guide scope on the Lassell reflecting telescope in the 1880s. The 6.5 inch telescope was originally purchased used from a Mr Corbett, and was on a mobile tripod; it was acquired as an expedition telescope for the 1874 Transit of Venus. In the early 21st century the telescope was normally free to visit, and could reached by going through a gift shop at the observatory when the facilities were open. However, it was also featured in an edutainment presentation called Great Equatorial Encounter and that experience cost the price of few pounds' currency. In the presentation there was multimedia and questions could be asked of a presenter.

Mounting

The mounting was designed by George Airy in the 1850s, for the older 13-inch refractor, in conjunction with the firm Ransomes and Simms. It is an equatorial design, that allows the telescope to rotate to compensate for the rotation of the Earth; this allows the telescope to stay fixed on certain point in the heavens. The telescope tube is mounted in a latticework of iron, that is mounted on each end on spindle that rest on a stone and metal pier. In the 1890s the mount was able to accommodate the 28-inch, and was thus re-used. Originally it was rotated by a clockwork drive powered by water, and later in the 20th century this was replaced by electric motor driven system. In 1897 it was said that the clockwork water drive that "the water clock in general drives it with great precision."

Domes

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Greenwich 28-inch refractor

Start with the simplest possible case. Write down what Greenwich 28-inch refractor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Greenwich 28-inch refractor 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 Greenwich 28-inch refractor 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 Greenwich 28-inch refractor

In research: Greenwich 28-inch refractor appears in science 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 Greenwich 28-inch refractor 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: Greenwich 28-inch refractor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Great refractors, Royal Observatory, Greenwich, so understanding it makes those chapters shorter.
In everyday life: Look for Greenwich 28-inch refractor 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Greenwich 28-inch refractor” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Greenwich 28-inch refractor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Greenwich 28-inch refractor 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 Greenwich 28-inch refractor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Greenwich 28-inch refractor in simple terms?

Why does Greenwich 28-inch refractor matter?

Because it connects several science 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 Greenwich 28-inch refractor?

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 Greenwich 28-inch refractor.