astronomy

XO-4

XO-4 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 XO-4 rather than just read about it. In short: XO-4 is a star located approximately 863 light-years away from Earth in the Lynx constellation. It has a magnitude of about 11 and cannot be seen with the naked eye but is visible through a small telescope.

Key takeaways

XO-4 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect XO-4 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of XO-4 from memory before moving on to harder problems.

Reference excerpt

XO-4 is a star located approximately 863 light-years away from Earth in the Lynx constellation. It has a magnitude of about 11 and cannot be seen with the naked eye but is visible through a small telescope. A search for a binary companion star using adaptive optics at MMT Observatory was negative. The star XO-4 is named Koit. The name was selected in the NameExoWorlds campaign by Estonia, during the 100th anniversary of the IAU. Koit is Estonian for dawn, and was named for a character in a folk tale written by Friedrich Robert Faehlmann.

Planetary system One known exoplanet, XO-4b, which is classified as a hot Jupiter, orbits XO-4. This exoplanet was discovered in 2008 by the XO Project using the transit method. It has been named Hämarik, meaning dusk, and referring to a character from the same Faehlmann story featuring Koit. The planetary orbit is misaligned with the stellar rotation.

Notes

References

External links "XO-4". Exoplanets. Archived from the original on 2016-03-03. Retrieved 2009-04-28.

Worked examples

Example 1 — a first encounter with XO-4

Start with the simplest possible case. Write down what XO-4 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 XO-4 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 XO-4 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 XO-4

In research: XO-4 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 XO-4 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: XO-4 is common in secondary-school and first-year university syllabi. It links to neighbouring topics F-type main-sequence stars, Lynx (constellation), Main-sequence-star stubs, so understanding it makes those chapters shorter.
In everyday life: Look for XO-4 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 XO-4 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what XO-4 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 XO-4 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is XO-4 in simple terms?

Why does XO-4 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 XO-4?

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 XO-4.