astronomy

Gliese 393

Gliese 393 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 393 rather than just read about it. In short: Gliese 393, or GJ 393, is a single star with an orbiting exoplanet companion in the equatorial constellation of Sextans, positioned about 1.5° to the NNW of Beta Sextantis. At an apparent visual magnitude of 9.65, it is much too faint to be seen with the unaided eye.

Key takeaways

Gliese 393 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 393 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 393 from memory before moving on to harder problems.

Reference excerpt

Gliese 393, or GJ 393, is a single star with an orbiting exoplanet companion in the equatorial constellation of Sextans, positioned about 1.5° to the NNW of Beta Sextantis. At an apparent visual magnitude of 9.65, it is much too faint to be seen with the unaided eye. This star is located at a distance of 22.9 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +8.3 km/s. It has a large proper motion, traversing the celestial sphere at the rate of 0.950″ per year. The net velocity of this star relative to the Sun is 32.9 km/s. It shares a similar space motion as members of the AB Doradus moving group, but is considered a random interloper. The stellar classification of GJ 393 is M2V, indicating this is a small red dwarf star that is generating energy through core hydrogen fusion. It is rotating slowly and appears to be chromospherically inactive, suggesting it is an older star; perhaps as much as 10 billion years old. The star has 43% of the mass of the Sun and 44.6% of the Sun's radius. The metallicity, what astronomers term the abundance of heavy elements, is lower than in the Sun. It is radiating just 2.7% of the Sun's luminosity from its photosphere at an effective temperature of 3,579 K.

Planetary system In 2019, one candidate planet was detected by the radial velocity method. It is classified as a hot super-Earth, with an orbital period of one week and a semimajor axis of 8.2 Gm. Longer period signals found in the data were interpreted as stellar activity. In 2021, the planet was confirmed as real after being detected independently in three different datasets.

References

Worked examples

Example 1 — a first encounter with Gliese 393

Start with the simplest possible case. Write down what Gliese 393 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 393 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 393 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 393

In research: Gliese 393 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 393 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 393 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 393 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 393 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 393 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 393 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 393 in simple terms?

Why does Gliese 393 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 393?

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 393.