astronomy

Gliese 676

Gliese 676 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 676 rather than just read about it. In short: Gliese 676 is a 10th-magnitude wide binary system of red dwarfs that has an estimated minimum separation of 800 AU with an orbital period of greater than 20,000 years. It is located approximately 54 light years away in the constellation Ara.

Key takeaways

Gliese 676 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 676 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 676 from memory before moving on to harder problems.

Reference excerpt

Gliese 676 is a 10th-magnitude wide binary system of red dwarfs that has an estimated minimum separation of 800 AU with an orbital period of greater than 20,000 years. It is located approximately 54 light years away in the constellation Ara. In 2009, a gas giant was found in orbit around the primary star, in addition to its confirmation in 2011 there was also a strong indication of a companion; the second gas giant was characterised in 2012, along with two much smaller planets.

Planetary system The first planet discovered, b, is a super-jovian first characterised in October 2009. The planet was formally announced in 2011, along with the first recognition of a trend not attributable to the companion star. Even after fitting a planet and a trend, it was noted that the residual velocities were still around 3.4 m/s, significantly larger than the instrumental errors of around 1.7 m/s. This tentatively implied the existence of other bodies in orbit, though nothing more could be said at the time. The star was a test case for the HARPS-TERRA software for better reduction of data from the HARPS spectrometer in early 2012. Even with significantly lower margins of error on the data, less data was accessible than what was used in 2011. Still, the team reached a very similar conclusion to the previous team with a model of a planet and a trend. The residual velocities were still somewhat excessive, giving more weight to the existence of other bodies in the system, though still no conclusions could be made. Between the time of the previous analysis and June 2012, the rest of the radial-velocity measurements used in 2011 were made public, allowing them to be reduced using HARPS-TERRA. These were then analysed via a Bayesian probability analysis, which was previously used to discover HD 10180 i and j, which confirmed planet b and made a first characterisation of planet c, which was previously only described as a trend. After the first two signals were introduced, the next most powerful signal was at around 35.5 days, with an analytic false alarm probability of 0.156. Through 104 trials, the false alarm probability was found to be 0.44%, low enough for it to be included as a periodic, planetary signal. With a minimum mass of around 11 Earths, the planet lies at the accepted border between Super-Earths and gaseous, Neptune-like bodies of 10 Earths. After accepting the third signal, a strong peak at 3.6 days became apparent. With a false alarm probability much lower than that of the previously accepted body, it was immediately accepted. With a minimum mass of around 4.5 Earths, it is a small Super-Earth. As of 2012, this system holds the record for the widest range of masses in a single planetary system, and also shows a hierarchy reminiscent of the Solar System, with the gas giants at large distances from the star while the smaller bodies are much closer-in. In 2016, the true mass of Gliese 676 Ab was measured via astrometry. A 2022 study revised this mass estimate, along with measuring the true mass of Gliese 676 Ac. There are two Super-Jupiter planets: "b" with a period of 1051 days (2.9 years) and a mass of 5.79 MJ, and "c" with a period of 13,900 days (38.1 years) and a mass of 13.49 MJ, which is at the borderline between planets and brown dwarfs.

Worked examples

Example 1 — a first encounter with Gliese 676

Start with the simplest possible case. Write down what Gliese 676 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 676 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 676 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 676

In research: Gliese 676 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 676 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 676 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ara (constellation), Binary stars, Durchmusterung objects, so understanding it makes those chapters shorter.
In everyday life: Look for Gliese 676 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 676 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 676 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 676 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 676 in simple terms?

Why does Gliese 676 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 676?

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 676.