astronomy

GJ 1245

GJ 1245 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 GJ 1245 rather than just read about it. In short: GJ 1245 (Gliese 1245) is a double star with components G 208-44 and G 208-45, located 15.2 light-years (4.7 parsecs) away in the constellation Cygnus. G 208-44 is itself a closer double star made up of two red dwarfs, while G 208-45 is also a red dwarf.

Key takeaways

GJ 1245 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GJ 1245 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GJ 1245 from memory before moving on to harder problems.

Reference excerpt

GJ 1245 (Gliese 1245) is a double star with components G 208-44 and G 208-45, located 15.2 light-years (4.7 parsecs) away in the constellation Cygnus. G 208-44 is itself a closer double star made up of two red dwarfs, while G 208-45 is also a red dwarf. GJ 1245 is the 43rd closest stellar system to the Solar System. GJ 1245 A and B are both active flare stars, and the pair are collectively designated V1581 Cygni. The largest of the three stars, GJ 1245 A (G 208-44 A) is only 12% the Sun's mass. Of the other two stars, GJ 1245 C (G 208-44 B), is closest to star A at 2 AU away; it is 8% of the Sun's mass. The third star, GJ 1245 B (G 208-45), is 27 AU away from star A, and is estimated to complete an orbit every 279 years. It is slightly smaller and less luminous than GJ 1245 A.

See also List of nearest stars

Notes

References

Further reading Harrington, R. S.; Dahn, C. C.; Kallarakal, V. V.; Guetter, H. H.; Riepe, B. Y.; Walker, R. L.; Pier, J. R.; Vrba, F. J.; Luginbuhl, C. B.; Harris, H. C.; Ables, H. D. (1993). "U.S. Naval Observatory photographic parallaxes - List IX". Astronomical Journal. 105 (4): 1571–1580. Bibcode:1993AJ....105.1571H. doi:10.1086/116537. Henry, Todd J.; Subasavage, John P.; Brown, Misty A.; Beaulieu, Thomas D.; Jao, Wei-Chun; Hambly, Nigel C. (2004). "The Solar Neighborhood. X. New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs". The Astronomical Journal. 128 (5): 2460–2473. arXiv:astro-ph/0408240. Bibcode:2004AJ....128.2460H. doi:10.1086/425052. S2CID 15759789. Smart, R. L.; Ioannidis, G.; Jones, H. R. A.; Bucciarelli, B.; Lattanzi, M. G. (2010). "Cool dwarfs stars from the Torino Observatory Parallax Program". Astronomy and Astrophysics. 514: A84. arXiv:1003.1465. Bibcode:2010A&A...514A..84S. doi:10.1051/0004-6361/200913424. S2CID 17961025. Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Berta-Thompson, Zachory K. (2014). "Trigonometric Parallaxes for 1507 Nearby Mid-to-late M Dwarfs". The Astrophysical Journal. 784 (2): 156. arXiv:1312.3241. Bibcode:2014ApJ...784..156D. doi:10.1088/0004-637X/784/2/156. S2CID 18789867. Table with parallaxes.

External links http://jumk.de/astronomie/near-stars/v1581-cygni.shtml http://www.answers.com/topic/list-of-nearest-stars?cat=travel http://www.richweb.f9.co.uk/astro/nearby_stars.htm

Illustrations

Worked examples

Example 1 — a first encounter with GJ 1245

Start with the simplest possible case. Write down what GJ 1245 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 GJ 1245 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 GJ 1245 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 GJ 1245

In research: GJ 1245 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 GJ 1245 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: GJ 1245 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cygnus (constellation), Gliese and GJ objects, Local Bubble, so understanding it makes those chapters shorter.
In everyday life: Look for GJ 1245 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 GJ 1245 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GJ 1245 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 GJ 1245 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GJ 1245 in simple terms?

Why does GJ 1245 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 GJ 1245?

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 GJ 1245.