2. Main guidelines for A&A style

Consistency in punctuation, capitalization, spelling, hyphenation, and abbreviation is essential in maintaining the highest standard possible in any journal. The following sections explain the general rules of the A&A house style.

2.1 Acronyms and abbreviations

All acronyms and abbreviations should be spelled out upon first appearance in the body of the text and be followed by the acronym in parentheses. Once a term and its acronym have been introduced, you should use the acronym thereafter.


  • The High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph was mounted at the ESO 3.6m telescope in La Silla in 2003.

Note 1: A sentence should not begin with an acronym or abbreviation. Adding an article before the name can sometimes work to fix this issue; otherwise, please write out the name in full.

Note 2: The abbreviations e.g. and i.e. are acceptable when used in parentheses or figure and table legends; however, they should always be expanded when they are part of the main text. The abbreviation “e.g.” in the body of the text can be replaced with “for example,” “for instance,” or “such as,” whereas in the main body of the text, “i.e.” should be replaced by “that is” or a similar phrase. When using e.g. and i.e. in parentheses, please make note that in UK convention, there is no comma (e.g. and i.e.) while in US style, there is a comma (e.g., and i.e.,) when abbreviated.

Note 3: When giving location indicators throughout the paper, Sect., Fig., Eq., and Col. should always be abbreviated and capitalized when referring to a specific item, except when they are at the beginning of a sentence in which case they should be written out (Section, Figure, Equation, and Column).

Examples: Sect. 2, Sects. 2 and 3; Fig. 1, Figs. 1-4; Eq. (1), Eqs. (1), (2); Col. 1, Cols. 1-3.

Note 4: Table is never abbreviated, although it is capitalized when followed by its designated number. When any of these words are not followed by a specific item number, they are not capitalized or abbreviated.


  • This result can be found in the next section, where Eqs. (5) and (6) are discussed.

2.2 Capitalization

When it comes to capitalization, only proper nouns (Poisson, Solar Orbiter) and terms derived from proper nouns (Gaussian) are capitalized; this also applies to cardinal directions (north, south, east, west), which are in lowercase unless forming part of a proper noun (Chandra Deep Field South).

When giving the full name of a measurement, method, or other scientific terms, do not use capitals unless it comes from a proper noun (e.g., Poisson; Poissonian), the acronym has been formed from a combination of uppercase and lowercase letters, or the acronym is formed from other than the first letters.

Note: Earth, Moon, Milky Way, Solar System, and Galaxy are always capitalized but only when referring to Earth’s own Galaxy. Objects outside of our Galaxy should be written in lowercase.

Examples: star formation (SF), Atlantic Ocean (AO), the Galactic center (GC, when referring to our Galaxy), galactic center (GC, when referring to another galaxy), LOw Frequency ARray (LOFAR)

2.3 Commas and listing items effectively

Use the serial comma (also known as the Oxford comma) between three or more items that are listed consecutively. If a conjunction is used (and, or), the third comma should come before it. The word respectively can be used to clarify relationships between multiple sets of data. A semicolon can be used to further distinguish several consecutive sets of items or two independent ideas that are part of a complex sentence.

General notes on commas:

  • Commas should be used after introductory sentences of three or more words.
  • Commas should be used when splitting up or moving around the individual parts of a sentence (clauses) to improve clarity, especially in the case of complex phrases or sentence structures.
  • Commas are not necessary between two parallel items in a sentence.


  • In this paper, the estimation of rotation, glide, and quadrupole parameters are presented in Figs. 10, 11, and 12, respectively. We set the bin size at 20 for ICRF1 and published our results in a previous paper.

2.4 Date format

The date format in a paper must be consistent. To avoid ambiguity between UK and US styles of dates, we ask for the month to be spelled out and cardinal endings left out.

Examples: 4 January 2004; 4 Jan 2004; January 4, 2004; Jan 4, 2004; 2004 January 4; 2004 Jan 4

2.5 Headings and titles

For titles and headings, only the first word should be capitalized unless it is a proper noun, copyrighted name, or a specific instrument. When a colon appears in the title, the second part of the title is treated as a subtitle and the first word should also be capitalized. Abbreviations in the titles or headings should be avoided unless it renders the title too long (i.e., more than three lines).

Note: A colon should only be used when joining together two related but independent ideas. For the text appearing after a colon, the first word is not capitalized unless it is a full sentence, a proper noun, or part of a title or section heading.

Examples of titles and headings:

  • Radio afterglows of binary neutron star mergers: A population study
  • NGC 346 massive star census. Nitrogen abundances for core burning B-type stars
  • 5. Discussion and conclusions
  • 5.1 Twisted quasar light curves

2.6 Measurements

Standard units of measurement (cm, au, kg, s, h) do not need to be introduced unless they are mentioned individually, without any specific value.


  • We measured the distance in kilometers. Our result is 13 678 km.

Note: The tilde symbol (~) should only be used before measurements (~ 5 au) but not before text. Its textual equivalent is “approximately,” “on the order of” (US), or “of the order of” (UK).

2.7 Numbers

Write out numbers and ordinal numbers below 11 when they are not used as a measurement.


  • This was the second time we attempted to carry out observations at 5 GHz using the VLBA over the course of 12 years.

2.8 Parenthesis

Use parentheses to provide additional information, such as acronyms, brief elaborations, and, of course, references. Please avoid lengthy or numerous parenthetical phrases. If the text in parentheses can stand alone as a sentence, the parentheses are probably not necessary. Avoid parenthesis within parentheses, except when it is part of a formula. This includes the year in a reference that is placed in parenthesis, where we also prefer no comma between the name and year but do expect the period after “et al.”: (Johnson et al. 1999). When the name is in the text, only the year is in parenthesis. Also avoid placing two sets of parentheses together.


  • The ALLWISE catalog (Mainzer et al. 2011) was compiled after combining the data obtained during the cryogenic and post-cryogenic survey (NEOWISE) phases. These differences were noted by Tisserand (2012) and also mentioned earlier on in this paper (see Sect. 4).

2.9 Things to avoid

  • Avoid beginning a sentence with a number, a formula, or a symbol (in addition to an abbreviation or acronym, as mentioned above). To avoid this, you can either rephrase the sentence, add an article, or (in the case of a number or acronym) spell out the number/acronym.
    • Example:
      Ten years ago, our team of researchers began studying this phenomenon.
  • Avoid the use of bullets or lists in the body of the text. Bullet lists may be permitted in the conclusion as long as they are properly introduced with at least two sentences and there are a few concluding sentences after the last point of the list.
  • Avoid the contraction of verbs. Please write out verbs in full without any contraction. Correct usage is: do not, cannot, will not, it is, it is not, etc.
  • Avoid long and numerous footnotes where possible. For lengthy descriptions, please include as much as possible in the main body of the text.
  • Avoid italics for indicating emphasis. If you wish to place emphasis on a word, quotation marks are recommended - single for papers written in UK style (‘) and double for papers in US style (“). Quotation marks should only be used for emphasis the first time you use the word or phrase.
  • Avoid using informal language because it often creates ambiguity. For example, when making comparisons or giving examples, the word like should be replaced by such as, for example, or for instance.
  • Avoid using lengthy quotes from other papers. When possible, it is best to summarize the point you wish to make and provide the appropriate reference.
  • To avoid potential confusion, seasons (e.g., summer, fall/autumn, winter, spring) should be replaced with months as they are different in the Northern and Southern Hemispheres.
  • Avoid using slashes in the body of the text because these should be reserved for equations, ratios, and specific pairings of instruments. In place of slashes, we recommend using and, or, or a hyphen, as appropriate.

Note: A&A uses the abbreviation S/N for signal-to-noise ratio to avoid confusion with supernova remnant (SNR). There is no need to write out the word “ratio” after S/N as this is already indicated by the slash.