astronomy

WD J2356−209

WD J2356−209 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 WD J2356−209 rather than just read about it. In short: WD J2356−209 (also known as WD 2354−211) is a white dwarf star located 65 pc (212 ly) away from the Earth. It is a very faint white dwarf, with an apparent visual magnitude of 21.03.

Key takeaways

WD J2356−209 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect WD J2356−209 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of WD J2356−209 from memory before moving on to harder problems.

Reference excerpt

WD J2356−209 (also known as WD 2354−211) is a white dwarf star located 65 pc (212 ly) away from the Earth. It is a very faint white dwarf, with an apparent visual magnitude of 21.03. Its visible spectrum is dominated by a broad absorption feature that has been attributed to pressure-broadened sodium D lines. The presence of this sodium absorption feature and the detection of spectral lines from other heavy elements (calcium, iron and magnesium) indicate that the photosphere of WD J2356−209 has been polluted by a recent rocky debris accretion episode. A detailed analysis of the spectrum of WD J2356−209 shows that the accreted planetesimal was abnormally sodium-rich, containing up to ten times more sodium than calcium. With an effective temperature of 4040 K, WD J2356−209 was the coolest metal-polluted white dwarf observed at the time (and also the oldest, with a white dwarf cooling age of about 8 Gyr).

See also List of exoplanets and planetary debris around white dwarfs WD J2147–4035 is the coldest and oldest metal-polluted white dwarf (as of September 2024) WD 2317+1830 is another cold metal-polluted white dwarf

References

External links Too much sodium turns a star blue 25 February 2019, Nathalie Ouellette

Worked examples

Example 1 — a first encounter with WD J2356−209

Start with the simplest possible case. Write down what WD J2356−209 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 WD J2356−209 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 WD J2356−209 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 WD J2356−209

In research: WD J2356−209 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 WD J2356−209 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: WD J2356−209 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cetus (constellation), White dwarf star stubs, White dwarfs, so understanding it makes those chapters shorter.
In everyday life: Look for WD J2356−209 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 “WD J2356−209” →

Affiliate

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

How to study WD J2356−209 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what WD J2356−209 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 WD J2356−209 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is WD J2356−209 in simple terms?

WD J2356−209 (also known as WD 2354−211) is a white dwarf star located 65 pc (212 ly) away from the Earth. It is a very faint white dwarf, with an apparent visual magnitude of 21.03.

Why does WD J2356−209 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 WD J2356−209?

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 WD J2356−209.