astronomy

Principal Galaxies Catalogue

Principal Galaxies Catalogue 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 Principal Galaxies Catalogue rather than just read about it. In short: The Principal Galaxies Catalogue (PGC) is an astronomical catalog published in 1989 that lists B1950 and J2000 equatorial coordinates and cross-identifications for 73,197 galaxies. It is based on the Lyon-Meudon Extragalactic Database (LEDA), which was originally started in 1983. 40,932 coordinates (56%) have standard deviations smaller than 10″.

Key takeaways

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

Reference excerpt

The Principal Galaxies Catalogue (PGC) is an astronomical catalog published in 1989 that lists B1950 and J2000 equatorial coordinates and cross-identifications for 73,197 galaxies. It is based on the Lyon-Meudon Extragalactic Database (LEDA), which was originally started in 1983. 40,932 coordinates (56%) have standard deviations smaller than 10″. A total of 131,601 names from the 38 most common sources are listed. Available mean data for each object are given:

49,102 morphological descriptions, 52,954 apparent major and minor axis, 67,116 apparent magnitudes, 20,046 radial velocities and 24,361 position angles. The Lyon-Meudon Extragalactic Database was eventually expanded into HyperLEDA, a database of a few million galaxies. Galaxies in the original PGC catalogue are numbered with their original PGC number in HyperLEDA. Numbers have also been assigned for the other galaxies, although for those galaxies not in the original PGC catalogue, it is not recommended to use that number as a name.

Examples

PGC 39058 PGC 39058 is a dwarf galaxy which is located approximately 14 million light-years away in the constellation of Draco. It is relatively nearby, however it is obscured by HD 106381, which is in front of the galaxy.

PGC 6240 PGC 6240 (also known as White Rose Galaxy) is a large lenticular galaxy in the constellation Hydrus. It is located about 346 million light-years away from Earth.

See also Category:Principal Galaxies Catalogue objects Astronomical catalogue

References

External links PGC info at ESO's archive of astronomical catalogues PGC readme at Centre de Données astronomiques de Strasbourg.

Illustrations

Worked examples

Example 1 — a first encounter with Principal Galaxies Catalogue

Start with the simplest possible case. Write down what Principal Galaxies Catalogue 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 Principal Galaxies Catalogue 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 Principal Galaxies Catalogue 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 Principal Galaxies Catalogue

In research: Principal Galaxies Catalogue 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 Principal Galaxies Catalogue 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: Principal Galaxies Catalogue is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1989 documents, 1989 in science, Astronomical catalogues of galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for Principal Galaxies Catalogue 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 Principal Galaxies Catalogue in 20 minutes

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

Frequently asked questions

What is Principal Galaxies Catalogue in simple terms?

Why does Principal Galaxies Catalogue 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 Principal Galaxies Catalogue?

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 Principal Galaxies Catalogue.