astronomy

WASP-21

WASP-21 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 WASP-21 rather than just read about it. In short: WASP-21, also named Tangra, is a G-type star (spectral type G3V) that has reached the end of its main sequence lifetime. It lies approximately 834 light-years away, in the constellation of Pegasus.

Key takeaways

WASP-21 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect WASP-21 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of WASP-21 from memory before moving on to harder problems.

Reference excerpt

WASP-21, also named Tangra, is a G-type star (spectral type G3V) that has reached the end of its main sequence lifetime. It lies approximately 834 light-years away, in the constellation of Pegasus. The star is relatively metal-poor, having 40% of heavy elements compared to the Sun. Kinematically, WASP-21 belongs to the thick disk of the Milky Way. It has an exoplanet named WASP-21b. A survey in 2012 failed to find any stellar companions to WASP-21.

Naming In 2019 the WASP-21 system was chosen as part of the NameExoWorlds campaign organised by the International Astronomical Union, which assigned each country a star and planet to be named. WASP-21 was assigned to Bulgaria. The winning proposal named the star Tangra after a deity worshipped by the early Bulgars, and the planet Bendida after a deity worshipped by the Thracians.

Planetary system In 2010 WASP-21 was discovered to host a hot Jupiter type planet by the Wide Angle Search for Planets (WASP), confirmed by radial velocity by the WASP team in 2010. Transit-timing variation analysis in 2015 did not find any additional planets in the system. In 2020, spectroscopic analysis found that the WASP-21b atmosphere is mostly cloudless and contains sodium.

References

Illustrations

Worked examples

Example 1 — a first encounter with WASP-21

Start with the simplest possible case. Write down what WASP-21 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 WASP-21 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 WASP-21 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 WASP-21

In research: WASP-21 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 WASP-21 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: WASP-21 is common in secondary-school and first-year university syllabi. It links to neighbouring topics G-type subgiants, Pegasus (constellation), Planetary systems with one confirmed planet, so understanding it makes those chapters shorter.
In everyday life: Look for WASP-21 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 WASP-21 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what WASP-21 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 WASP-21 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is WASP-21 in simple terms?

WASP-21, also named Tangra, is a G-type star (spectral type G3V) that has reached the end of its main sequence lifetime. It lies approximately 834 light-years away, in the constellation of Pegasus.

Why does WASP-21 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 WASP-21?

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 WASP-21.