astronomy

GJ 9827

GJ 9827 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 9827 rather than just read about it. In short: GJ 9827 is a star in the constellation of Pisces. It is a K-type main-sequence star with an apparent magnitude of 10.25.

Key takeaways

GJ 9827 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 9827 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GJ 9827 from memory before moving on to harder problems.

Reference excerpt

GJ 9827 is a star in the constellation of Pisces. It is a K-type main-sequence star with an apparent magnitude of 10.25. It is 97 light-years (30 parsecs) away, based on parallax. The rotation period of the star could not be determined as of 2020, and could be either around 15 or 30 days, depending on the interpretation of available data.

Planetary system GJ 9827 has 3 transiting planets seen by the Kepler space observatory in their K2 survey. As of October 2017, it was the closest star discovered to have transiting exoplanets found by either the Kepler or K2 missions. The planets (b, c, d) have radii of 1.62, 1.27, and 2.09 times that of the Earth, and periods of 1.209, 3.648, and 6.201 days (ratios 1:3:5). Because of its close distance the system is considered an excellent target for studying atmospherics of exoplanets. In late 2017, the masses of all three planets were determined using the Planet Finder Spectrograph on the Magellan II Telescope. Planet b was found to be very iron-rich, planet c appears to be mainly rocky, and planet d is a typical volatile-rich planet. GJ 9827b is noted as being one of the densest planets yet found, with its mass containing about ≥50% iron. More precise radial velocity measurements released in late February 2018 revealed that all three planets have a lower density than Earth and have some amount of volatiles in their compositions. GJ 9827b and c are mainly rocky (containing less than 1% mass fraction of water, and negligible helium and hydrogen) with very thin volatile envelopes, while GJ 9827d is more akin to a mini-Neptune. The loss of primordial atmosphere was indirectly confirmed in 2020, as no helium was detected at GJ 9827 d. With a mass of about 1.5 M🜨, GJ 9827c is one of the least massive planets detected with radial velocity. The atmospheres for GJ 9827b and GJ 9827d were not detected at all in 2021 observations. A 2023 study using the Hubble Space Telescope detected water vapor in the atmosphere of GJ 9827 d. This study describes the planet as a potential ocean world. A 2024 study used the Échelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) of the European Southern Observatory to model the stellar activity of GJ 9827 and derive masses, orbital periods and radial velocity amplitudes of planets b, c, and d. A 2024 study by the James Webb Space Telescope found that GJ 9827 d has a steam H2O atmosphere, making it the first discovered steam world.

References

External links Abrar, Umer (28 September 2017). "Kepler Space Telescope Just Discovered One Of The Most Important Planet Yet". The Space Academy.

Illustrations

Worked examples

Example 1 — a first encounter with GJ 9827

Start with the simplest possible case. Write down what GJ 9827 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 9827 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 9827 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 9827

In research: GJ 9827 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 9827 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 9827 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 GJ 9827 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 9827 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GJ 9827 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 9827 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GJ 9827 in simple terms?

GJ 9827 is a star in the constellation of Pisces. It is a K-type main-sequence star with an apparent magnitude of 10.25.

Why does GJ 9827 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 9827?

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 9827.