astronomy

Kepler-20

Kepler-20 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 Kepler-20 rather than just read about it. In short: Kepler-20 is a star about 934 light-years (286 parsecs) from Earth in the constellation Lyra with a system of at least five, and possibly six, known planets. The apparent magnitude of this star is 12.51, so it cannot be seen with the unaided eye.

Key takeaways

Kepler-20 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Kepler-20 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Kepler-20 from memory before moving on to harder problems.

Reference excerpt

Kepler-20 is a star about 934 light-years (286 parsecs) from Earth in the constellation Lyra with a system of at least five, and possibly six, known planets. The apparent magnitude of this star is 12.51, so it cannot be seen with the unaided eye. Viewing it requires a telescope with an aperture of 15 cm (6 in) or more. It is slightly smaller than the Sun, with 94% of the Sun's radius and about 91% of the Sun's mass. The effective temperature of the photosphere is slightly cooler than that of the Sun at 5466 K, giving it the characteristic yellow hue of a stellar class G8 star. The abundance of elements other than hydrogen or helium, what astronomers term the metallicity, is approximately the same as in the Sun. It may be older than the Sun, although the margin of error here is relatively large.

Planetary system

On December 20, 2011, the Kepler Space Telescope team reported the discovery of a five-planet system containing three small gas giants and the first two Earth-sized extrasolar planets, Kepler-20e (the first known extrasolar planet smaller than Earth orbiting a main-sequence star) and Kepler-20f, orbiting a Sun-like star. Although the planets are Earth-sized, they are not Earth-like in the respect that they are much closer to their star than Earth, and are hence not near the habitable zone, with expected surface temperatures of 760 °C (1,400 °F) and 427 °C (801 °F), respectively. The three other Neptune-sized planets in the system, Kepler-20b, Kepler-20c, and Kepler-20d, all orbit similarly close to the star. Only upper limits on the masses of e and f are known. Their masses are uncertain as they are too small to detect via radial velocity with current technology. As of 2023, Kepler-20e is known to be less massive than Earth. A 2016 study detected a sixth planet in the system based on radial velocity observations. Kepler-20g may be a non-transiting Neptunian world. However, the existence of this planet was challenged in 2019, and a non-detection was reported in 2023. Another 2023 study listed this planet, though the data used was identical to the 2016 study except for the addition of a single data point, and the dispute was not addressed. All planets are at small near resonances; proceeding outwards, they are 3:2, 4:2, 2:1, 4:1. The planetary orbits in current form are highly sensitive to perturbations caused by outer planets, therefore assuming stability, no additional gas giant planets can be located closer than 30 AU from the parent star.

See also 55 Cancri Kepler-11 Kepler-33 List of multiplanetary systems

References

External links

Multimedia: Video (01:33) NASA Discovers First Earth-like Exoplanet Orbiting A Sun-like Star.

Worked examples

Example 1 — a first encounter with Kepler-20

Start with the simplest possible case. Write down what Kepler-20 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 Kepler-20 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 Kepler-20 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 Kepler-20

In research: Kepler-20 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 Kepler-20 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: Kepler-20 is common in secondary-school and first-year university syllabi. It links to neighbouring topics G-type main-sequence stars, Kepler-20, Kepler objects of interest, so understanding it makes those chapters shorter.
In everyday life: Look for Kepler-20 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 Kepler-20 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Kepler-20 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 Kepler-20 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Kepler-20 in simple terms?

Why does Kepler-20 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 Kepler-20?

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 Kepler-20.