astronomy

K2-72

K2-72 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 K2-72 rather than just read about it. In short: K2-72 (also designated EPIC 206209135) is a cool red dwarf star of spectral class M2V located about 217 light-years (67 parsecs) away from the Earth in the constellation of Aquarius. It is known to host four planets, all similar in size to Earth, with one of them residing within the habitable zone.

Key takeaways

K2-72 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect K2-72 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of K2-72 from memory before moving on to harder problems.

Reference excerpt

K2-72 (also designated EPIC 206209135) is a cool red dwarf star of spectral class M2V located about 217 light-years (67 parsecs) away from the Earth in the constellation of Aquarius. It is known to host four planets, all similar in size to Earth, with one of them residing within the habitable zone.

Nomenclature and history K2-72 also has the 2MASS catalogue number J22182923-0936444. Its EPIC (Ecliptic Plane Input Catalog) number is 206209135. The star's planetary companions were discovered by NASA's Kepler Mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from the perspective of Earth. The name K2-72 derives directly from the fact that the star is the catalogued 72nd star discovered by the K2 mission to have confirmed planets. The designation b, c, d, and e derives from the order of discovery. The designation of b is given to the first planet orbiting a given star, and e to the last. In the case of K2-72, there were four planets, so only letters b to e are used. At first the planets were all thought to be smaller than Earth. However, in 2017, new analysis by Martinez et al. and Courtney Dressing found that K2-72 was significantly larger than previous estimates, and found that the planets were all larger than Earth, although all are still expected to be rocky.

Stellar characteristics K2-72 is a M-type star that is approximately 27% the mass of and 33% the radius of the Sun, according to the analysis done by Dressing et al. The results found by Martinez et al. suggest a larger star, with about 36% the radius and mass of the Sun. Both give a luminosity estimate between 0.013 and 0.015 solar luminosities. It has a surface temperature of between 3360 and 3370 K and its age is unknown. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 15.309. Therefore, it is too dim to be seen with the naked eye and can only be observed with a telescope.

Planetary system The star is known to host four planets, all likely to be rocky. Only one (K2-72e) is currently known to reside inside the habitable zone, although K2-72c may straddle the inner edge.

References

Worked examples

Example 1 — a first encounter with K2-72

Start with the simplest possible case. Write down what K2-72 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 K2-72 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 K2-72 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 K2-72

In research: K2-72 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 K2-72 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: K2-72 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aquarius (constellation), M-type main-sequence stars, Planetary systems with four confirmed planets, so understanding it makes those chapters shorter.
In everyday life: Look for K2-72 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 K2-72 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what K2-72 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 K2-72 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is K2-72 in simple terms?

Why does K2-72 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 K2-72?

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 K2-72.