astronomy

NGC 6811

NGC 6811 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 NGC 6811 rather than just read about it. In short: NGC 6811 is an open cluster in the constellation of Cygnus, near the constellation of Lyra. It has an angular size half that of the full Moon and includes about 1000 stars of roughly similar magnitude.

Key takeaways

NGC 6811 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NGC 6811 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 6811 from memory before moving on to harder problems.

Reference excerpt

NGC 6811 is an open cluster in the constellation of Cygnus, near the constellation of Lyra. It has an angular size half that of the full Moon and includes about 1000 stars of roughly similar magnitude. It has also been called "The Hole in the Cluster" or "Hole in a Cluster" because of its dark center.

Features NGC 6811 lies far away from the galactic plane, a feature it shares with many other old open clusters. It is 1107 ± 90 parsecs (about 3,285 light years) distant and approximately 4-6 parsecs (14–20 light years) in diameter, with a total luminosity of 2100 suns. Approximately 1.00 ± 0.17 billion years old, the cluster probably contained some 6000 stars at birth, but gravitational interactions and stellar evolution have since reduced the number substantially. A recent study reported 377 confirmed member stars, with spectral types ranging from mid-F to early K, and surface temperatures relatively similar to the Sun's. The same study argued that the original cluster population likely included 8 O-type stars and 125 B-type stars, but all have evolved off the main sequence and are undetectable. Sixteen stars have been observed to vary in brightness, twelve of which are Delta Scuti variables. The cluster's Trumpler classification is III 1r—it is "a rich cluster with equally bright stars with no noticeable central concentration". The stars do, however, have an unusual (if not concentrated) distribution, with an apparent stellar corona surrounding the core, leaving the impression of a hole.

Observation NGC 6811 was first observed by John Herschel in 1829 and was added to his General Catalogue of Nebulae and Clusters in 1864. The cluster has been the subject of study by the Kepler mission, with the aim of characterizing its stars' rotation rate, age, and distance to help the hunt for exoplanets. NGC 6811 is best observed from Earth in the Northern Hemisphere in summer. In these conditions it lies close to the zenith during the night, northeast of Delta Cygni. It is considered an aesthetically pleasant object for amateur astronomers, even if the brightest members are just 10th magnitude objects. It appears as a hazy patch in 10x binoculars, but it is best seen at around 70x with a moderate-aperture telescope. It has been described by amateur astronomers as a "smoke ring of stars" or "a jeweled mask a woman might wear at a masquerade ball".

Planets Two planets (Kepler 66b and Kepler 67b), orbiting Sun-like stars in the NGC 6811 cluster, have been discovered by the Kepler mission using the transit method. Both planets are smaller than Neptune and are both the first sub-Jupiter planets and the first transiting planets discovered orbiting stars within an open cluster. Given that the age and distance of the cluster have been accurately measured, the two planets are among the few of which age and distance are accurately known. This finding suggests that the frequency of planets in clusters is similar to that in stars not belonging to clusters or associations and that planets can form and survive in environments more crowded and violent than the one of our own Sun.

Illustrations

Worked examples

Example 1 — a first encounter with NGC 6811

Start with the simplest possible case. Write down what NGC 6811 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 NGC 6811 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 NGC 6811 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 NGC 6811

In research: NGC 6811 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 NGC 6811 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: NGC 6811 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cygnus (constellation), Kepler space telescope, NGC objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 6811 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 NGC 6811 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 6811 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 NGC 6811 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 6811 in simple terms?

Why does NGC 6811 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 NGC 6811?

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 NGC 6811.