astronomy

Gliese 42

Gliese 42 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 42 rather than just read about it. In short: Gliese 42 is a star in the southern constellation of Sculptor. It is too faint to be seen with the naked eye, having an apparent visual magnitude of +7.2.

Key takeaways

Gliese 42 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 42 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Gliese 42 from memory before moving on to harder problems.

Reference excerpt

Gliese 42 is a star in the southern constellation of Sculptor. It is too faint to be seen with the naked eye, having an apparent visual magnitude of +7.2. The annual parallax shift of 71.7 mas provides a distance estimate of 45 light years. It has a relatively high proper motion, advancing 0.62 arcseconds across the sky per annum, and is moving closer to the Sun with a radial velocity of −13 km/s. The spectrum of the star matches a stellar classification of K2.5 V (k), indicating it is an ordinary K-type main-sequence star that is generating energy through hydrogen fusion at its core. It is radiating 29% of the Sun's luminosity from its photosphere at an effective temperature of 4,921 K. The star has 74% of the Sun's radius.

Debris disk An infrared excess has been detected around this star, most likely indicating the presence of a circumstellar disk at a radius of 45.7 astronomical units (6.84×109 km; 4.25×109 mi). The temperature of this dust was initially estimated as 30 K (−243.2 °C; −405.7 °F) according to measurement by Herschel Space Observatory. Later that measurement was deemed questionable, and fixed temperature of 62 K (−211.2 °C; −348.1 °F) was obtained in 2020.

References

External links University of Heidelberg, The. "ARICNS ARI Data Base for Nearby Stars". Archived from the original on 28 September 2012. Retrieved 8 May 2012. University of Strasbourg, The. "SIMBAD star database". Archived from the original on 2 October 2018. Retrieved 8 May 2012. University of Hamburg, The. "NEXXUS 2 - The database for Nearby X-ray and extreme UV emitting Stars". Archived from the original on 4 March 2016. Retrieved 8 May 2012. Sol Stations, The. "K stars within 100 light-years". Archived from the original on 24 December 2017. Retrieved 8 May 2012.

Worked examples

Example 1 — a first encounter with Gliese 42

Start with the simplest possible case. Write down what Gliese 42 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 42 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 42 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 42

In research: Gliese 42 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 42 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 42 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Durchmusterung objects, Gliese and GJ objects, Henry Draper Catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for Gliese 42 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 42 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gliese 42 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 42 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gliese 42 in simple terms?

Gliese 42 is a star in the southern constellation of Sculptor. It is too faint to be seen with the naked eye, having an apparent visual magnitude of +7.2.

Why does Gliese 42 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 42?

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 42.