astronomy

List of galaxies

List of galaxies 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 List of galaxies rather than just read about it. In short: An estimated 2 trillion+ galaxies occupy the observable universe. On the order of 100,000 galaxies make up the Local Supercluster, and about 51 galaxies are in the Local Group (see list of nearest galaxies for a complete list).

Key takeaways

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

Reference excerpt

An estimated 2 trillion+ galaxies occupy the observable universe. On the order of 100,000 galaxies make up the Local Supercluster, and about 51 galaxies are in the Local Group (see list of nearest galaxies for a complete list). The first attempts at systematic catalogues of galaxies were made in the 1960s, with the Catalogue of Galaxies and Clusters of Galaxies listing 29,418 galaxies and galaxy clusters, and with the Morphological Catalogue of Galaxies, a putatively complete list of galaxies with photographic magnitude above 15, listing 30,642. In the 1980s, the Lyons Groups of Galaxies listed 485 galaxy groups with 3,933 member galaxies. Galaxy Zoo is a project aiming at a more comprehensive list: launched in July 2007, it has classified over one million galaxy images from The Sloan Digital Sky Survey, The Hubble Space Telescope and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey.

Named galaxies

This is a list of galaxies that are well known by something other than an entry in a catalog or list, or a set of coordinates, or a systematic designation.

Naked-eye galaxies This is a list of galaxies that are visible to the naked eye, for at the very least, keen-eyed observers in a very dark-sky environment that is high in altitude, during clear and stable weather.

Sagittarius Dwarf Spheroidal Galaxy is not listed, because it is not discernible as being a separate galaxy in the sky.

Observational firsts

Prototypes This is a list of galaxies that became prototypes for a class of galaxies.

Closest and most distant-known galaxies by type

Closest galaxies

Most distant galaxies

Timeline notes MACS0647-JD, discovered in 2012, with z=10.7, does not appear on this list because it has not been confirmed with a spectroscopic redshift. UDFy-38135539, discovered in 2009, with z=8.6, does not appear on this list because its claimed redshift is disputed. Follow-up observations have failed to replicate the cited redshift measurement. A1689-zD1, discovered in 2008, with z=7.6, does not appear on this list because it has not been confirmed with a spectroscopic redshift. Abell 68 c1 and Abell 2219 c1, discovered in 2007, with z=9, do not appear on this list because they have not been confirmed. IOK4 and IOK5, discovered in 2007, with z=7, do not appear on this list because they have not been confirmed with a spectroscopic redshift. Abell 1835 IR1916, discovered in 2004, with z=10.0, does not appear on this list because its claimed redshift is disputed. Some follow-up observations have failed to find the object at all. STIS 123627+621755, discovered in 1999, with z=6.68, does not appear on this list because its redshift was based on an erroneous interpretation of an oxygen emission line as a hydrogen emission line. BR1202-0725 LAE, discovered in 1998 at z=5.64 does not appear on the list because it was not definitively pinned. BR1202-0725 (QSO 1202-07) refers to a quasar that the Lyman alpha emitting galaxy is near. The quasar itself lies at z=4.6947 BR2237-0607 LA1 and BR2237-0607 LA2 were found at z=4.55 while investigating around the quasar BR2237-0607 in 1996. Neither of these appear on the list because they were not definitively pinned down at the time. The quasar itself lies at z=4.558 Two absorption dropouts in the spectrum of quasar BR 1202-07 (QSO 1202-0725, BRI 1202-0725, BRI1202-07) were found, one in early 1996, another later in 1996. Neither of these appear on the list because they were not definitively pinned down at the time. The early one was at z=4.38, the later one at z=4.687, the quasar itself lies at z=4.695 In 1986, a gravitationally lensed galaxy forming a blue arc was found lensed by galaxy cluster CL 2224-02 (C12224 in some references). However, its redshift was only determined in 1991, at z=2.237, by which time, it would no longer be the most distant galaxy known. An absorption drop was discovered in 1985 in the light spectrum of quasar PKS 1614+051 at z=3.21 This does not appear on the list because it was not definitively fixed down. At the time, it was claimed to be the first non-QSO galaxy found beyond redshift 3. The quasar itself is at z=3.197 In 1975, 3C 123 was incorrectly determined to lie at z=0.637 (actually z=0.218). From 1964 to 1997, the title of most distant object in the universe was held by a succession of quasars. That list is available at list of quasars. In 1958, clusters Cl 0024+1654 and Cl 1447+2619 were estimated to have redshifts of z=0.29 and z=0.35, respectively. However, no galaxy was spectroscopically determined.

Galaxies by brightness and power

Galaxies by mass and density

Galaxies by size

Interacting galaxies

Galaxy mergers

Galaxies with some other notable feature

Illustrations

Worked examples

Example 1 — a first encounter with List of galaxies

Start with the simplest possible case. Write down what List of galaxies 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 List of galaxies 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 List of galaxies 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 List of galaxies

In research: List of galaxies 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 List of galaxies 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: List of galaxies is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lists of galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for List of galaxies 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 List of galaxies in 20 minutes

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

Frequently asked questions

What is List of galaxies in simple terms?

Why does List of galaxies 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 List of galaxies?

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 List of galaxies.