astronomy

Gliese 221

Gliese 221 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 Gliese 221 rather than just read about it. In short: Gliese 221 (GJ 221), also known as BD-06 1339, is a star with an exoplanetary companion in the equatorial constellation of Orion. It is too faint to be visible to the naked eye, having an apparent visual magnitude of 9.70 and an absolute magnitude of 8.15.

Key takeaways

Gliese 221 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Gliese 221 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 221 from memory before moving on to harder problems.

Reference excerpt

Gliese 221 (GJ 221), also known as BD-06 1339, is a star with an exoplanetary companion in the equatorial constellation of Orion. It is too faint to be visible to the naked eye, having an apparent visual magnitude of 9.70 and an absolute magnitude of 8.15. Using parallax measurements, the distance to this system can be estimated as 66.2 light-years. It is receding from the Sun with a radial velocity of +23 km/s. This is a high proper motion star, traversing the celestial sphere at an angular rate of 0.333″·yr−1. This is a late K-type or early M-type main-sequence star with a stellar classification of K7V/M0V. It has 72% of the mass and 61% of the radius of the Sun. The star is roughly 4.4 billion years old and is depleted in heavy elements, containing just 46% of solar abundance of iron. It is an active star and the level of chromospheric activity has been found to vary significantly over time. The star is radiating 10% of the luminosity of the Sun from its photosphere at an effective temperature of 4,324 K.

Planetary system From 2003 to 2012, the star was under observance from the High Accuracy Radial Velocity Planet Searcher (HARPS). It is becoming less active and this reduced activity allowed for lower-mass planetary measurements to be made. A super-Venus planet, and an eccentric Neptune / Saturn in the habitable zone, were deduced by radial velocity in January 2013. They were confirmed in May 2013. In January 2014, a candidate planet d was proposed. The planet Gliese 221b (BD-06 1339 b) is not transiting the disk of the parent star, and its existence was disputed in 2022.

References

Worked examples

Example 1 — a first encounter with Gliese 221

Start with the simplest possible case. Write down what Gliese 221 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 Gliese 221 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 Gliese 221 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 Gliese 221

In research: Gliese 221 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 Gliese 221 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: Gliese 221 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Gliese and GJ objects, Hipparcos objects, so understanding it makes those chapters shorter.
In everyday life: Look for Gliese 221 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 Gliese 221 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 221 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 Gliese 221 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 221 in simple terms?

Why does Gliese 221 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 Gliese 221?

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 Gliese 221.