astronomy

PH2

PH2 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 PH2 rather than just read about it. In short: PH2, also known as Kepler-86, or KIC 12735740 (2MASS J19190326+5157453), is an F-type main-sequence star 1,120 light-years (340 parsecs) distant within the constellation Cygnus. Roughly the size and temperature of the Sun, PH2 gained prominence when it was known to be the host of one of 42 planet candidates detected by the Planet Hunters citizen science project in its second data release.

Key takeaways

PH2 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PH2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PH2 from memory before moving on to harder problems.

Reference excerpt

PH2, also known as Kepler-86, or KIC 12735740 (2MASS J19190326+5157453), is an F-type main-sequence star 1,120 light-years (340 parsecs) distant within the constellation Cygnus. Roughly the size and temperature of the Sun, PH2 gained prominence when it was known to be the host of one of 42 planet candidates detected by the Planet Hunters citizen science project in its second data release. The candidate orbiting around PH2, known as PH2b, had been determined to have a spurious detection probability of only 0.08%, thus effectively confirming its existence as a planet. Located in its parent star's habitable zone, PH2b (or Kepler-86b) is a Jupiter-size gas giant which could in theory host a natural satellite suitable for hosting life. The report of the confirmed detection of PH2b was submitted on January 3, 2013. It was discovered by amateur Pole Rafał Herszkowicz using his laptop and access to the Internet project with data from the Kepler space observatory.

History of detection PH2 b was detected, along with 42 other planet candidates, in archival data from Kepler by the Planet Hunters project, in which human volunteers analyze the light curves of Kepler target stars, searching for planetary transit signals which may be missed by computer programs. Previous work by Planet Hunters helped to confirm the existence of PH1b, a Neptune-mass planet within a four-star system. All of the candidates in the study, including PH2b, were identified by citizen scientists Abe J. Hoekstra, Thomas Lee Jacobs, Daryll LaCourse, Hans Martin Schwengler, Rafał Herszkowicz and Mike Chopin among others, with the help of Yale University astronomers. In addition to PH2b itself, twenty other planet candidates were found which are located in the habitable zones of their host stars; however, these have a relatively high probability of spurious detection and may well come from non-planetary sources. Although the planet's initial detection was made using Kepler data, PH2's stellar spectra, required to rule out background stars or faint companions with planets as sources for the observed transits, were collected using the HIRES instrument at the W. M. Keck Observatory. Results of observations confirmed the existence of PH2b with "99.9 percent confidence."

Planetary system PH2 is host to one confirmed planet, PH2b, orbiting with a period of about 282 days, placing it and any possible moons in the habitable zone. The temperature in the upper atmosphere of the planet could range from 185 K (−88 °C; −127 °F) to 303 K (30 °C; 86 °F). A moon of PH2b would likely have "a rocky core, plus a greenhouse atmosphere of some sort that could have liquid water on its surface" in the words of the researchers, thus further improving its prospects for habitability. In 2019, the mass of the planet was measured by radial velocity, showing it to be close in mass to Saturn.

See also Amateur exoplanet discoveries Exomoon Habitability of natural satellites HIP 41378 f Kepler 1625 b I Kepler 1708 b I

Notes

References

Footnotes

External links Kepler Mission - NASA. KIC-12735740 Star on Star Finder/cthreepo Video (00:52) - Journey To Exoplanet "PH2 b"

Worked examples

Example 1 — a first encounter with PH2

Start with the simplest possible case. Write down what PH2 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 PH2 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 PH2 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 PH2

In research: PH2 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 PH2 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: PH2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cygnus (constellation), F-type main-sequence stars, Kepler objects of interest, so understanding it makes those chapters shorter.
In everyday life: Look for PH2 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “PH2” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study PH2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PH2 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 PH2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PH2 in simple terms?

Why does PH2 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 PH2?

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 PH2.

PH2